Subjects -> ASTRONOMY (Total: 94 journals)
Showing 1 - 46 of 46 Journals sorted alphabetically
Advances in Astronomy     Open Access   (Followers: 49)
Annual Review of Astronomy and Astrophysics     Full-text available via subscription   (Followers: 50)
Annual Review of Earth and Planetary Sciences     Full-text available via subscription   (Followers: 67)
Artificial Satellites     Open Access   (Followers: 21)
Astrobiology     Hybrid Journal   (Followers: 11)
Astronomical & Astrophysical Transactions: The Journal of the Eurasian Astronomical Society     Hybrid Journal   (Followers: 7)
Astronomical Review     Open Access   (Followers: 5)
Astronomische Nachrichten     Hybrid Journal   (Followers: 4)
Astronomy & Geophysics     Hybrid Journal   (Followers: 49)
Astronomy and Astrophysics     Full-text available via subscription   (Followers: 67)
Astronomy and Computing     Hybrid Journal   (Followers: 6)
Astronomy Letters     Hybrid Journal   (Followers: 22)
Astronomy Reports     Hybrid Journal   (Followers: 22)
Astronomy Studies Development     Open Access   (Followers: 15)
Astroparticle Physics     Hybrid Journal   (Followers: 10)
Astrophysical Bulletin     Hybrid Journal   (Followers: 4)
Astrophysics     Hybrid Journal   (Followers: 35)
Astrophysics and Space Science     Hybrid Journal   (Followers: 49)
Astrophysics and Space Sciences Transactions (ASTRA)     Open Access   (Followers: 60)
Astropolitics: The International Journal of Space Politics & Policy     Hybrid Journal   (Followers: 13)
Celestial Mechanics and Dynamical Astronomy     Hybrid Journal   (Followers: 15)
Chinese Astronomy and Astrophysics     Full-text available via subscription   (Followers: 25)
Colloid Journal     Hybrid Journal   (Followers: 2)
Comptes Rendus : Physique     Open Access   (Followers: 2)
Computational Astrophysics and Cosmology     Open Access   (Followers: 6)
Earth and Planetary Science Letters     Hybrid Journal   (Followers: 143)
Earth, Moon, and Planets     Hybrid Journal   (Followers: 47)
Earth, Planets and Space     Open Access   (Followers: 77)
EAS Publications Series     Full-text available via subscription   (Followers: 8)
EPL Europhysics Letters     Partially Free   (Followers: 8)
Experimental Astronomy     Hybrid Journal   (Followers: 38)
Expert Opinion on Astronomy and Astrophysics     Open Access   (Followers: 8)
Extreme Life, Biospeology & Astrobiology - International Journal of the Bioflux Society     Full-text available via subscription   (Followers: 4)
Few-Body Systems     Hybrid Journal   (Followers: 1)
Foundations of Physics     Hybrid Journal   (Followers: 40)
Frontiers in Astronomy and Space Sciences     Open Access   (Followers: 15)
Galaxies     Open Access   (Followers: 6)
Globe, The     Full-text available via subscription   (Followers: 3)
Gravitation and Cosmology     Hybrid Journal   (Followers: 6)
Icarus     Hybrid Journal   (Followers: 71)
International Journal of Advanced Astronomy     Open Access   (Followers: 21)
International Journal of Astrobiology     Hybrid Journal   (Followers: 4)
International Journal of Astronomy     Open Access   (Followers: 22)
International Journal of Astronomy and Astrophysics     Open Access   (Followers: 36)
International Journal of Satellite Communications Policy and Management     Hybrid Journal   (Followers: 15)
International Letters of Chemistry, Physics and Astronomy     Open Access   (Followers: 8)
ISRN Astronomy and Astrophysics     Open Access   (Followers: 14)
Journal for the History of Astronomy     Full-text available via subscription   (Followers: 20)
Journal of Astrobiology & Outreach     Open Access   (Followers: 5)
Journal of Astronomical Instrumentation     Open Access   (Followers: 3)
Journal of Astrophysics     Open Access   (Followers: 33)
Journal of Astrophysics and Astronomy     Open Access   (Followers: 58)
Journal of Atmospheric and Solar-Terrestrial Physics     Hybrid Journal   (Followers: 133)
Journal of Geophysical Research : Planets     Full-text available via subscription   (Followers: 116)
Journal of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 136)
Journal of High Energy Astrophysics     Full-text available via subscription   (Followers: 25)
Kinematics and Physics of Celestial Bodies     Hybrid Journal   (Followers: 11)
KronoScope     Hybrid Journal   (Followers: 1)
Macalester Journal of Physics and Astronomy     Open Access   (Followers: 5)
Monthly Notices of the Royal Astronomical Society     Hybrid Journal   (Followers: 13)
Monthly Notices of the Royal Astronomical Society : Letters     Hybrid Journal   (Followers: 2)
Nature Astronomy     Hybrid Journal   (Followers: 14)
New Astronomy     Hybrid Journal   (Followers: 26)
New Astronomy Reviews     Full-text available via subscription   (Followers: 19)
Nonlinear Dynamics     Hybrid Journal   (Followers: 19)
NRIAG Journal of Astronomy and Geophysics     Open Access   (Followers: 4)
Physics of the Dark Universe     Open Access   (Followers: 4)
Planetary and Space Science     Hybrid Journal   (Followers: 106)
Planetary Science     Open Access   (Followers: 52)
Proceedings of the International Astronomical Union     Full-text available via subscription   (Followers: 2)
Publications of the Astronomical Society of Australia     Hybrid Journal   (Followers: 3)
Publications of the Astronomical Society of Japan     Hybrid Journal   (Followers: 4)
Research & Reviews : Journal of Space Science & Technology     Full-text available via subscription   (Followers: 20)
Research in Astronomy and Astrophysics     Full-text available via subscription   (Followers: 38)
Revista Mexicana de AstronomĂ­a y AstrofĂ­sica     Open Access   (Followers: 3)
Science China : Physics, Mechanics & Astronomy     Full-text available via subscription   (Followers: 4)
Science China Physics, Mechanics & Astronomy     Hybrid Journal   (Followers: 4)
Solar Physics     Hybrid Journal   (Followers: 29)
Solar System Research     Hybrid Journal   (Followers: 15)
Space Science International     Open Access   (Followers: 118)
Space Science Reviews     Hybrid Journal   (Followers: 92)
Space Weather     Full-text available via subscription   (Followers: 27)
Transport and Aerospace Engineering     Open Access   (Followers: 13)
Universe     Open Access   (Followers: 6)
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Number of Followers: 6  

  This is an Open Access Journal Open Access journal
ISSN (Print) 2218-1997
Published by MDPI Homepage  [84 journals]
  • Universe, Vol. 8, Pages 249: A Mesofractal Model of Interstellar

    • Authors: Vladimir V. Uchaikin, Ilya I. Kozhemyakin
      First page: 249
      Abstract: The interstellar medium (ISM), serving as a background for the propagation of cosmic rays (CRs) and other information carriers, has a complex ragged structure. Being chaotically scattered over interstellar space, together with the magnetic field perturbations frozen in them, CRs are connected with each other by a network of magnetic field lines creating long-range correlations of a power-law type, similar to those observed in the spatial distribution of galaxies. These lines solving interstellar transfer problems require the choice of an ISM model, adequately and concisely representing their statistical properties. This article discusses one such model, the Uchaikin–Zolotarev model: a four-parameter approximation of the power spectrum spatial correlations, derived from the generalized Ornstein–Zernike equation. The numerical analysis confirmed that this approximation satisfactorily agrees with the numerical data obtained in the quasi-linear model of plasma turbulence.
      Citation: Universe
      PubDate: 2022-04-19
      DOI: 10.3390/universe8050249
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 250: Generalized Darmois–Israel Junction

    • Authors: Chong-Sun Chu, Hai Siong Tan
      First page: 250
      Abstract: We present a general method to derive the appropriate Darmois–Israel junction conditions for gravitational theories with higher-order derivative terms by integrating the bulk equations of motion across the singular hypersurface. In higher-derivative theories, the field equations can contain terms which are more singular than the Dirac delta distribution. To handle them appropriately, we formulate a regularization procedure based on representing the delta function as the limit of a sequence of classical functions. This procedure involves imposing suitable constraints on the extrinsic curvature such that the field equations are compatible with the singular source being a delta distribution. As explicit examples of our approach, we demonstrate in detail how to obtain the generalized junction conditions for quadratic gravity, F(R) theories, a 4D low-energy effective action in string theory, and action terms that are Euler densities. Our results are novel, and refine the accuracy of previously claimed results in F(R) theories and quadratic gravity. In particular, when the coupling constants of quadratic gravity are those for the Gauss–Bonnet case, our junction conditions reduce to the known ones for the latter obtained independently by boundary variation of a surface term in the action. Finally, we briefly discuss a couple of applications to thin-shell wormholes and stellar models.
      Citation: Universe
      PubDate: 2022-04-19
      DOI: 10.3390/universe8050250
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 251: General Deflections in Deflected AMSB

    • Authors: Fei Wang, Ying-Kai Zhang
      First page: 251
      Abstract: The (extra)ordinary gauge mediation extension of deflected AMSB scenarios can be interesting because it can accommodate together the deflection in the Kahler potential and the superpotential. We derive the analytical expressions for soft SUSY breaking parameters in such EOGM extension of deflected AMSB scenarios with the presence of both types of deflections. The Landau pole and proton decay constraints are also discussed.
      Citation: Universe
      PubDate: 2022-04-19
      DOI: 10.3390/universe8050251
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 252: The Solar-Electric Sail: Application to
           Interstellar Migration and Consequences for SETI

    • Authors: Gregory Lee Matloff
      First page: 252
      Abstract: The Solar-Electric Sail accelerates by reflecting positively charged solar wind ions. If it is used to propel an interstellar migration mission, its interstellar cruise velocity relative to the home star cannot exceed the solar wind velocity. In an effort to analytically determine interstellar cruise velocity for a 107 kg generation ship, a constant solar wind velocity within the heliosphere of a Sun-like star of 600 km/s is assumed. The solar wind proton density at 1 AU is also considered constant at 10 protons per cubic centimeter. Solar wind density is assumed to decrease with the inverse square of solar distance. It is shown that, to maintain sufficient acceleration to achieve an interstellar cruise velocity about 70% of the solar wind velocity, the radius of the sail’s electric field is enormous—greater than 105 km. Because the solar wind velocity and density are not constant, field strength must be varied rapidly to compensate for solar wind variation. Although not competitive with the ultimate theoretical performance of solar-photon sail propelled migrations departing from Sun-like stars, the solar-electric sail might be superior in this application for migration from dim K and M main sequence stars. Such migrations conducted during close stellar encounters might have durations < 1000 terrestrial years. If only a tiny fraction of M dwarf stars host star-faring civilizations, a significant fraction of Milky Way galaxy planetary systems may have been inhabited, even if no major advances over currently postulated interstellar transportation systems are postulated. SETI theoreticians should consider this when estimating the effects of interstellar colonization.
      Citation: Universe
      PubDate: 2022-04-19
      DOI: 10.3390/universe8050252
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 253: Axion-like Particles Implications for
           High-Energy Astrophysics

    • Authors: Giorgio Galanti, Marco Roncadelli
      First page: 253
      Abstract: We offer a pedagogical introduction to axion-like particles (ALPs) as far as their relevance for high-energy sstrophysics is concerned, from a few MeV to 1000 TeV. This review is self-contained, in such a way to be understandable even to non-specialists. Among other things, we discuss two strong hints at a specific ALP that emerge from two very different astrophysical situations. More technical matters are contained in three Appendices.
      Citation: Universe
      PubDate: 2022-04-20
      DOI: 10.3390/universe8050253
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 254: Cosmological Parameter Estimation Using
           Current and Future Observations of Strong Gravitational Lensing

    • Authors: Jing-Zhao Qi, Wei-Hong Hu, Yu Cui, Jing-Fei Zhang, Xin Zhang
      First page: 254
      Abstract: The remarkable development of cosmology benefits from the increasingly improved measurements of cosmic distances, including absolute distances and relative distances. In recent years, however, the emerged cosmological tensions have motivated us to explore independent and precise late-universe probes. The two observational effects of strong gravitational lensing (SGL), the velocity dispersions of lens galaxies and the time delays between multiple images can provide measurements of relative and absolute distances, respectively, and their combination makes it possible to break the degeneracies between cosmological parameters and enable tight constraints on them. In this paper, we combine the observed 130 SGL systems with velocity-dispersion measurements and 7 SGL systems with time-delay measurements to constrain dark-energy cosmological models. It is found that the combination of the two effects does not significantly break the degeneracies between cosmological parameters as expected. However, with the simulations of 8000 SGL systems with well-measured velocity dispersions and 55 SGL systems with well-measured time delays based on the forthcoming LSST survey, we find that the combination of two effects can significantly break the parameter degeneracies, and make the constraint precision of cosmological parameters meet the standard of precision cosmology. We conclude that the observations of SGL will become a useful late-universe probe for precisely measuring cosmological parameters.
      Citation: Universe
      PubDate: 2022-04-20
      DOI: 10.3390/universe8050254
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 255: NEAR: A New Station to Study Neutron-Induced
           Reactions of Astrophysical Interest at CERN-n_TOF

    • Authors: Gianpiero Gervino, Oliver Aberle, Ana-Paula Bernardes, Nicola Colonna, Sergio Cristallo, Maria Diakaki, Salvatore Fiore, Alice Manna, Cristian Massimi, Pierfrancesco Mastinu, Alberto Mengoni, Riccardo Mucciola, Elizabeth Musacchio González, Nikolas Patronis, Elisso Stamati, Pedro Vaz, Rosa Vlastou
      First page: 255
      Abstract: We present NEAR, a new experimental area at the CERN-n_TOF facility and a possible setup for cross section measurements of interest to nuclear astrophysics. This was recently realized with the aim of performing spectral-averaged neutron-capture cross section measurements by means of the activation technique. The recently commissioned NEAR station at n_TOF is now ready for the physics program, which includes a preliminary benchmark of the proposed idea. Based on the results obtained by dedicated Monte Carlo simulations and calculation, a suitable filtering of the neutron beam is expected to enable measurements of Maxwellian Averaged Cross Section (MACS) at different temperatures. To validate the feasibility of these studies we plan to start the measurement campaign by irradiating several isotopes whose MACS at different temperatures have recently been or are planned to be determined with high accuracy at n_TOF, as a function of energy in the two time-of-flight measurement stations. For instance, the physical cases of 88Sr(n,γ), 89Y(n,γ), 94Zr(n,γ) and 64Ni(n,γ) are discussed. As the neutron capture on 89Y produces a pure β-decay emitter, we plan to test the possibility to perform activation measurements on such class of isotopes as well. The expected results of these measurements would open the way to challenging measurements of MACS by the activation technique at n_TOF, for rare and/or exotic isotopes of interest for nuclear astrophysics.
      Citation: Universe
      PubDate: 2022-04-20
      DOI: 10.3390/universe8050255
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 256: Methodologies to Measure the CP Structure of
           the Higgs Yukawa Coupling to Tau Leptons

    • Authors: Andrea Cardini
      First page: 256
      Abstract: One of the central goals of the Large Hadron Collider has been the search, and later the study, of the Higgs boson. Its coupling structure under charge conjugation and parity (CP) symmetries has been extensively investigated as a probe for new physics. This paper presents a review of the methods collected in the literature to access the CP structure of the Yukawa coupling of the Higgs boson to tau leptons at proton colliders. A new notation is introduced to classify already existing methods, highlighting their common features and favoring the investigation of new, more performing alternatives.
      Citation: Universe
      PubDate: 2022-04-21
      DOI: 10.3390/universe8050256
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 257: How the Big Bang Ends Up Inside a Black Hole

    • Authors: Enrique Gaztanaga
      First page: 257
      Abstract: The standard model of cosmology assumes that our Universe began 14 Gyrs (billion years) ago from a singular Big Bang creation. This can explain a vast range of different astrophysical data from a handful of free cosmological parameters. However, we have no direct evidence or fundamental understanding of some key assumptions: Inflation, Dark Matter and Dark Energy. Here we review the idea that cosmic expansion originates instead from gravitational collapse and bounce. The collapse generates a Black Hole (BH) of mass M≃5×1022M⊙ that formed 25 Gyrs ago. As there is no pressure support, the cold collapse can continue inside in free fall until it reaches atomic nuclear saturation (GeV), when is halted by Quantum Mechanics, as two particles cannot occupy the same quantum state. The collapse then bounces like a core-collapse supernovae, producing the Big Bang expansion. Cosmic acceleration results from the BH event horizon. During collapse, perturbations exit the horizon to re-enter during expansion, giving rise to the observed universe without the need for Inflation or Dark Energy. Using Ockham’s razor, this makes the BH Universe (BHU) model more compelling than the standard singular Big Bang creation.
      Citation: Universe
      PubDate: 2022-04-21
      DOI: 10.3390/universe8050257
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 258: Correction: Buompane et al. Recent
           Achievements of the ERNA Collaboration. Universe 2022, 8, 135

    • Authors: Raffaele Buompane, Antonino Di Leva, Lucio Gialanella, Gianluca Imbriani, Lizeth Morales-Gallegos, Mauro Romoli
      First page: 258
      Abstract: In the original publication [...]
      Citation: Universe
      PubDate: 2022-04-22
      DOI: 10.3390/universe8050258
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 259: Moffat MOdified Gravity (MOG)

    • Authors: Sreekanth Harikumar
      First page: 259
      Abstract: Scalar Tensor Vector Gravity (STVG) or MOdified Gravity (MOG) is a metric theory of gravity with dynamical scalar fields and a massive vector field introduced in addition to the metric tensor. In the weak field approximation, MOG modifies the Newtonian acceleration with a Yukawa-like repulsive term due to a Maxwell–Proca type Lagrangian. This associates matter with a fifth force and a modified equation of motion. MOG has been successful in explaining galaxy rotation curves, cosmological observations and all other solar system observations without the need for dark matter. In this article, we discuss the key concepts of MOG theory. Then, we discuss existing observational bounds on MOG weak field parameters. In particular, we will present our original results obtained from the X-COP sample of galaxy clusters.
      Citation: Universe
      PubDate: 2022-04-24
      DOI: 10.3390/universe8050259
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 260: Testing Lorentz Violation with IceCube

    • Authors: Huiming Zhang, Lili Yang
      First page: 260
      Abstract: Lorentz violation (LV) induced by Quantum Gravity has been tested at much lower energies than the Planck scale with more and more observational evidence. In recent studies, the time of flight difference between the TeV neutrino and MeV photon from Gamma Ray Bursts (GRBs) have been used to constrain the LV energy scale, based on the energy-dependent speed variation. Here, we performed a correlation study between the updated 7.5 year high-energy starting events (HESE), neutrino alert events detected by IceCube, and a full sample of more than 7000 GRBs, and we found six GRB-neutrino candidates, including four alerts and two track events. We obtained the first order energy scale of quantum gravity, namely EQG=8−5+15×1017GeV, which was consistent with other authors‘ work. We suggest that neutrinos and anti-neutrinos can be identified, respectively, due to the delay or advance of the observed time. For future point source search study of neutrinos, the arrival time difference of different particles may have to be taken into account.
      Citation: Universe
      PubDate: 2022-04-24
      DOI: 10.3390/universe8050260
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 261: The 3D Direct Simulation Monte Carlo Study of
           Europa’s Gas Plume

    • Authors: Wei-Ling Tseng, Ian-Lin Lai, Wing-Huen Ip, Hsiang-Wen Hsu, Jong-Shinn Wu
      First page: 261
      Abstract: Europa has been spotted as having water outgassing activities by space- and ground-based telescopes as well as reanalysis of the Galileo data. We adopt a 3D Direct Simulation Monte Carlo (DSMC) model to investigate the observed plume characteristics of Europa assuming that supersonic expansion originated from the subsurface vent. With a parametric study of the total gas production rate and initial gas bulk velocity, the gas number density, temperature and velocity information of the outgassing plumes from various case studies were derived. Our results show that the plume gases experience acceleration through mutual collisions and adiabatic cooling when exiting from the surface. The central part of the plume with relatively large gas production rates (1029 and 1030 H2O s−1) was found to sustain thermal equilibrium and near continuum condition. Column density maps integrated along two different viewing angles are presented to demonstrate the importance of the projection effect on remote sensing diagnostics. Finally, the density profiles at different altitudes are provided to prepare for observations of Europa’s plumes including upcoming spacecraft missions such as JUICE and Europa Clipper.
      Citation: Universe
      PubDate: 2022-04-24
      DOI: 10.3390/universe8050261
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 262: Weak Deflection Angle and Greybody Bound of
           Magnetized Regular Black Hole

    • Authors: Wajiha Javed, Sibgha Riaz, Ali Övgün
      First page: 262
      Abstract: In this paper, we examine the weak deflection angle and greybody bound for a magnetized regular black hole. For this purpose, we apply the Gauss–Bonnet theorem on the black hole and obtain the deflection angle in plasma and non-plasma mediums. Moreover, we investigate graphically the effect of impact parameter on the deflection angle for regular black hole in both mediums. We examine that the deflection angle goes to infinity when the impact parameter approaches zero. We also observe that the deflection angle shows negative behaviour at q=0.6 and q=2.09, but at 0.6<q<2.09, the angle shows positive behaviour. Furthermore, we study the rigorous bound phenomenon of the greybody factor in the background for a magnetized regular black hole. Later, we analyse the graphical behaviour of greybody bound with respect to different values of ω and observe that, at small values of ω, the bound increases, but for large values, the bound decreases. After that, we examine that, when we put G=1, l=0 and q=0, all results for the magnetized regular black hole solution reduce into results of the Schwarzschild black hole solution.
      Citation: Universe
      PubDate: 2022-04-25
      DOI: 10.3390/universe8050262
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 263: Is the Hubble Crisis Connected with the
           Extinction of Dinosaurs'

    • Authors: Leandros Perivolaropoulos
      First page: 263
      Abstract: It has recently been suggested that a gravitational transition of the effective Newton’s constant Geff by about 10%, 50–150 Myrs ago could lead to the resolution of both the Hubble crisis and the growth tension of the standard ΛCDM model. Hints for such an abrupt transition with weaker gravity at times before the transition, have recently been identified in Tully–Fisher galactic mass-velocity data, and also in Cepheid SnIa calibrator data. Here we use Monte-Carlo simulations to show that such a transition could significantly increase (by a factor of 3 or more) the number of long period comets (LPCs) impacting the solar system from the Oort cloud (semi-major axis of orbits ≳104AU). This increase is consistent with observational evidence from the terrestrial and lunar cratering rates, indicating that the impact flux of kilometer sized objects increased by at least a factor of 2 over that last 100 Myrs compared to the long term average. This increase may also be connected with the Chicxulub impactor event that produced the Cretaceous–Tertiary (K-T) extinction of 75% of life on Earth (including dinosaurs) about 66 Myrs ago. We use Monte-Carlo simulations to show that for isotropic Oort cloud comet distribution with initially circular orbits, random velocity perturbations (induced e.g., by passing stars and/or galactic tidal effects), lead to a deformation of the orbits that increases significantly when Geff increases. A 10% increase in Geff leads to an increase in the probability of the comets to enter the loss cone and reach the planetary region (pericenter of less than 10 AU) by a factor that ranges from 5% (for velocity perturbation much smaller than the comet initial velocity) to more than 300% (for total velocity perturbations comparable with the initial comet velocity).
      Citation: Universe
      PubDate: 2022-04-26
      DOI: 10.3390/universe8050263
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 264: Effects of a Finite Volume in the Phase
           Structure of QCD

    • Authors: Nallaly Berenice Mata Carrizal, Enrique Valbuena Ordóñez, Adrián Jacob Garza Aguirre, Francisco Javier Betancourt Sotomayor, José Rubén Morones Ibarra
      First page: 264
      Abstract: Working in the SU(2) flavor version of the NJL model, we study the effect of taking a finite system volume on a strongly interacting system of quarks, and, in particular, the location of the chiral phase transition and the CEP. We consider two shapes for the volume, spherical and cubic regions with different sizes and different boundary conditions. To analyze the QCD phase diagram, we use a novel criterion to study the crossover zone. A comparison between the results obtained from the two different shapes and several boundary conditions is carried out. We use the method of Multiple Reflection Expansion to determine the density of states and three kinds of boundary conditions over the cubic shape. These boundary conditions are: periodic, anti-periodic and stationary boundary conditions on the quark fields.
      Citation: Universe
      PubDate: 2022-04-26
      DOI: 10.3390/universe8050264
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 265: Crossing of Phantom Divide Line in Model of
           Interacting Tsallis Holographic Dark Energy

    • Authors: Artyom V. Astashenok, Alexander Tepliakov
      First page: 265
      Abstract: We consider a Tsallis holographic dark energy model with interaction between dark energy and matter. The density of dark energy is taken as ρd∼3C2/L4−2γ, where C, γ are constants. The event horizon is chosen as the characteristic scale L. The cosmological dynamics of the universe are analyzed, with special attention paid to the possibility of crossing the phantom line weff=−1. It is shown that for certain values of parameters this may occur not only once, but also twice.
      Citation: Universe
      PubDate: 2022-04-27
      DOI: 10.3390/universe8050265
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 266: Avoiding Bias in Measurements of Fundamental
           Constants from High Resolution Quasar Spectra

    • Authors: John K. Webb, Chung-Chi Lee, Dinko Milaković
      First page: 266
      Abstract: Recent advances in spectroscopic instrumentation and calibration methods dramatically improve the quality of quasar spectra. Supercomputer calculations show that, at high spectral resolution, procedures used in some previous analyses of spacetime variations of fundamental constants are likely to generate spurious measurements, biased systematically towards a null result. Developments in analysis methods are also summarised and a prescription given for the analysis of new and forthcoming data.
      Citation: Universe
      PubDate: 2022-04-27
      DOI: 10.3390/universe8050266
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 267: Bayesian Methods for Inferring Missing Data
           in the BATSE Catalog of Short Gamma-Ray Bursts

    • Authors: Amir Shahmoradi, Joshua Alexander Osborne, Fatemeh Bagheri
      First page: 267
      Abstract: The knowledge of the redshifts of Short-duration Gamma-Ray Bursts (SGRBs) is essential for constraining their cosmic rates and thereby the rates of related astrophysical phenomena, particularly Gravitational Wave Radiation (GWR) events. Many of the events detected by gamma-ray observatories (e.g., BATSE, Fermi, and Swift) lack experimentally measured redshifts. To remedy this, we present and discuss a generic data-driven probabilistic modeling framework to infer the unknown redshifts of SGRBs in the BATSE catalog. We further explain how the proposed probabilistic modeling technique can be applied to newer catalogs of SGRBs and other astronomical surveys to infer the missing data in the catalogs.
      Citation: Universe
      PubDate: 2022-04-28
      DOI: 10.3390/universe8050267
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 268: Effective Actions for Regge Piecewise Flat
           Quantum Gravity

    • Authors: Aleksandar Miković
      First page: 268
      Abstract: We review the construction of the path integral and the corresponding effective action for the Regge formulation of General Relativity under the assumption that the short-distance structure of the spacetime is not a smooth 4-manifold, but a piecewise linear manifold based on a triangulation of a smooth 4-manifold. We point out that the exponentially damped 4-volume path-integral measure does not give a finite path integral, although it can be used for the construction of the perturbative effective action. We modify the 4-volume measure by multiplying it by an inverse power of the product of the edge-lengths such that the new measure gives a finite path integral while it retains all the nice features of the unmodified measure.
      Citation: Universe
      PubDate: 2022-04-29
      DOI: 10.3390/universe8050268
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 269: Causality in a Qubit-Based Implementation of
           a Quantum Switch

    • Authors: Carlos Sabín
      First page: 269
      Abstract: We introduce a qubit-based version of the quantum switch, consisting of a variation of the Fermi problem. Two qubits start in a superposition state in which one qubit is excited and the other is in the ground state. However, it is not defined which is the excited qubit. Then, after some time, if a photon is detected, we know that it must have experienced an emission by one atom and then an absorption and re-emission by the other one, but the ordering of the emission events by both qubits is undefined. While it is tempting to refer to this scenario as one with indefinite causality or a superposition of causal orders, we show that there is still a precise notion of causality: the probability of excitation of each atom is totally independent of the other one when the times are short enough to prevent photon exchange.
      Citation: Universe
      PubDate: 2022-05-04
      DOI: 10.3390/universe8050269
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 270: Dust Formation in the Wind of AGB
           Stars—The Effects of Mass, Metallicity and Gas-Dust Drift

    • Authors: Silvia Tosi, Flavia Dell’Agli, Erendira Huerta-Martinez, Paolo Ventura
      First page: 270
      Abstract: Dust production in the wind of stars evolving through the asymptotic giant branch is investigated by using a stationary wind model, applied to results from stellar evolution modelling. Results regarding 1–8M⊙ stars of metallicities Z=0.014 (solar) and Z=2×10−3 are compared, to infer the role played by stellar mass and chemical composition on the dust formation process. We find a dichotomy in mass: stars of (initial) mass below ∼3M⊙ produce silicates and alumina dust before they become carbon stars, then carbonaceous dust; the higher mass counterparts produce only silicates and alumina dust, in quantities that scale with metallicity. The presence of drifts with average drift velocities ∼5 Km/s leads to higher dust formation rates owing to the higher growth rates of the dust grains of the different species. However, no significant changes are found in the overall optical depths, because the higher rate of dust formations favours a fast expansion of the wind, that prevents further significant production of dust. As far as oxygen-rich stars are concerned, the presence of drifts makes the main dust component to change from olivine to pyroxene. The release of the assumption that the number density of the seed particles is independent of the dust species considered affects dust formation in the wind of carbon stars: a factor 10 reduction in the density of the seeds of SiC leads to bigger sized SiC grains, and partly inhibits the formation of solid carbon, since the wind is accelerated and the densities in the carbon formation zone are smaller. No substantial differences are found in the winds of oxygen-rich stars.
      Citation: Universe
      PubDate: 2022-05-05
      DOI: 10.3390/universe8050270
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 271: MASTER Real-Time Multi-Message Observations
           of High Energy Phenomena

    • Authors: Lipunov, Kornilov, Zhirkov, Kuznetsov, Gorbovskoy, Budnev, Buckley, Lopez, Serra-Ricart, Francile, Tyurina, Gress, Balanutsa, Antipov, Vlasenko, Topolev, Chasovnikov, Svertilov, Podesta, Podesta, Minkina, Tlatov, Yurkov, Gabovich, Ershova, Senik, Kuvshinov
      First page: 271
      Abstract: This review considers synchronous and follow-up MASTER Global Robotic Net optical observations of high energy astrophysical phenomena such as fast radio bursts (FRB), gamma-ray bursts (including prompt optical emission polarization discovery), gravitational-wave events, detected by LIGO/VIRGO (including GW170817 and independent Kilonova discovery), high energy neutrino sources (including the detection of IC-170922A progenitor) and others. We report on the first large optical monitoring campaign of the closest at that moment radio burster FRB 180916.J0158+65 simultaneously with a radio burst. We obtained synchronous limits on the optical flux of the FRB 180916.J0158+65 and FRB 200428 (soft gamma repeater SGR 1935+2154)(The CHIME/FRB Collaboration, Nature 2020, 587) at 155093 MASTER images with the total exposure time equal to 2,705,058 s, i.e., 31.3 days. It follows from these synchronous limitations that the ratio of the energies released in the optical and radio ranges does not exceed 4 × 105. Our optical monitoring covered a total of 6 weeks. On 28 April 2020, MASTER automatically following up on a Swift alert began to observe the galactic soft gamma repeater SGR 1935+2154 experienced another flare. On the same day, radio telescopes detected a short radio burst FRB 200428 and MASTER-Tavrida telescope determined the best prompt optical limit of FRB/SGR 1935+2154. Our optical limit shows that X-ray and radio emissions are not explained by a single power-law spectrum. In the course of our observations, using special methods, we found a faint extended afterglow in the FRB 180916.J0158+65 direction associated with the extended emission of the host galaxy.
      Citation: Universe
      PubDate: 2022-05-05
      DOI: 10.3390/universe8050271
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 272: Oscillating Magnetized Color Superconducting
           Quark Stars

    • Authors: Marcos Osvaldo Celi, Mauro Mariani, Milva Gabriela Orsaria, Lucas Tonetto
      First page: 272
      Abstract: The main objective of this work is to study the structure, composition, and oscillation modes of color superconducting quark stars with intense magnetic fields. We adopted the MIT bag model within the color superconductivity CFL framework, and we included the effects of strong magnetic fields to construct the equation of state of stable quark matter. We calculated observable quantities, such as the mass, radius, frequency, and damping time of the oscillation fundamental f mode of quark stars, taking into account current astrophysical constraints. The results obtained show that color superconducting magnetized quark stars satisfy the constraints imposed by the observations of massive pulsars and gravitational wave events. Furthermore, the quantities associated with the oscillation f mode of these objects fit the universal relationships for compact objects. In the context of the new multi-messenger gravitational wave astronomy era and the future asteroseismology of neutron stars, we hope that our results contribute to the understanding of the behavior of dense matter and compact objects.
      Citation: Universe
      PubDate: 2022-05-06
      DOI: 10.3390/universe8050272
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 273: Spectral and Timing Properties of H 1743-322
           in the “Faint” 2005 Normal Outburst

    • Authors: Aijun Dong, Chang Liu, Qijun Zhi, Ziyi You, Qibin Sun, Bowen Du
      First page: 273
      Abstract: H 1743-322 is a well-known black hole X-ray binary (BH XRBs) that has been observed in several outbursts over the past. In this work, we have performed the spectral and timing analysis of H 1743-322 during the “faint” 2005 outburst for the first time with the RXTE/PCA data. In this outburst, the spectral and timing parameters (e.g., Tin, Γ, Rin, rms and QPOs, etc.) presented an obvious change and a q-like pattern was found in the Hardness Intensity Diagram (HID), which often named as the hysteresis effect of BH XRBs. The radius of the innermost stable circular orbit was constrained as RISCO∼3.50 Rg, which predicts that H 1743-322 is a lower-spin black hole. We further explored the correlation between timing and spectral properties. The relation of photon index Γ and X-ray flux, F3–25keV, presented a transition between negative and positive correlation when the X-ray luminosity, L3–25keV, is above and below a critical X-ray luminosity, LX,crit≃2.55×10−3 LEdd, which can be well explained by the Shakura-Sunyaev disk–corona model (SSD-corona) and advection-dominated accretion flow (ADAF). We also found the tight linear, negative correlation between photon index Γ and the total fractional rms. Since the amount of soft photons from the accretion disk seems invariable, an increase of the number of soft photons will dilute the variability from the harder photons. Therefore, the softer the X-ray spectra will result in the smaller total fractional rms. The above results suggested that the 2005 outburst of H 1743-322 was a normal outburst and H 1743-322 represented similar properties with other black hole X-ray binaries.
      Citation: Universe
      PubDate: 2022-05-06
      DOI: 10.3390/universe8050273
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 274: The Effects of Elemental Abundances on
           Fitting Supernova Remnant Models to Data

    • Authors: Denis A. Leahy
      First page: 274
      Abstract: Models for supernova remnant (SNR) evolution can be used to determine the energy of the explosion, the age of the SNR, and the density of the surrounding medium by matching observations. Observed SNR properties derived from the X-ray spectrum include the electron temperature (kTe) and emission measure (EM) of the shocked gas. SNR models are based on hydrodynamic solutions for density, pressure, and velocity. The relations between these and kTe or EM depend on the three inputs of composition, ionization state, and electron-ion temperature ratio (Te/TI). The standard definitions and the XSPEC definitions for kTe and EM have important differences that are not well-known. The same definition used by observers of SNRs must be used in models for correct interpretation. Here, the effects of the three inputs on standard and on XSPEC versions of kTe and EM are investigated, with examples. The ratio of standard EM to the XSPEC value ranges widely, between ∼10−3 to ∼1, with smallest ratios for gas with low hydrogen abundance. The standard kTe differs from the XSPEC value by less than a few percent. For the illustrative example SNR J0049-7314, the ejecta component is shown to be consistent with core-collapse composition and a stellar wind environment.
      Citation: Universe
      PubDate: 2022-05-07
      DOI: 10.3390/universe8050274
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 275: Solar Radio Bursts Associated with In Situ
           Detected Energetic Electrons in Solar Cycles 23 and 24

    • Authors: Rositsa Miteva, Susan W. Samwel, Svetoslav Zabunov
      First page: 275
      Abstract: The first comprehensive analysis between the in situ detected solar energetic electrons (SEEs) from ACE/EPAM satellite and remotely observed radio signatures in solar cycles (SCs) 23 and 24 (1997–2019) is presented. The identified solar origin of the SEEs (in terms of solar flares, SFs, and coronal mass ejections, CMEs) is associated with solar radio emission of types II, III and IV, where possible. Occurrence rates are calculated as a function of the radio wavelength, from the low corona to the interplanetary space near Earth. The tendencies of the different burst appearances with respect to SC, helio-longitude, and SEE intensity are also demonstrated. The corresponding trends of the driver (in terms of median values of the SF class and CME projected speed) are also shown. A comparison with the respective results when using solar energetic protons is presented and discussed.
      Citation: Universe
      PubDate: 2022-05-09
      DOI: 10.3390/universe8050275
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 276: On the Non-Abelian U-Duality of 11D

    • Authors: Edvard T. Musaev
      First page: 276
      Abstract: In this work, we generalise the procedure of the non-abelian T-duality based on a B-shift and a sequence of formal abelian T-dualities in non-isometric directions to 11-dimensional backgrounds. This consists of a C-shift followed by either a formal (abelian) U-duality transformation or taking an IIB section. By construction, this is a solution generating transformation. We investigate the restrictions and applicability of the procedure and find that it can provide supergravity solutions for the SL(5) exceptional Drinfeld algebra only when the isometry algebra of the sigma-model target space decomposes into a direct sum. This is consistent with examples known in the literature.
      Citation: Universe
      PubDate: 2022-05-09
      DOI: 10.3390/universe8050276
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 277: Goldstone States as Non-Local Hidden

    • Authors: Luca Fabbri
      First page: 277
      Abstract: We consider the theory of spinor fields in polar form, where the spinorial true degrees of freedom are isolated from their Goldstone states, and we show that these carry information about the frames which is not related to gravitation, so that their propagation is not restricted to be either causal or local: we use them to build a model of entangled spins where a singlet possesses a uniform rotation that can be made to collapse for both states simultaneously regardless their spatial distance. Models of entangled polarizations with similar properties are also sketched. An analogy with the double-slit experiment is also presented. General comments on features of Goldstone states are given.
      Citation: Universe
      PubDate: 2022-05-09
      DOI: 10.3390/universe8050277
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 278: Bound Orbits and Epicyclic Motions around
           Renormalization Group Improved Schwarzschild Black Holes

    • Authors: Hou-Yu Lin, Xue-Mei Deng
      First page: 278
      Abstract: We study timelike particles’ bound orbits around renormalization group improved Schwarzschild black holes (RGISBHs), which originate from renormalization group improvement of the Einstein–Hilbert action by using the running Newton constant. By considering the secular periastron precession for the timelike particles orbiting around RGISBHs, we found that it is not feasible to distinguish such black holes from Schwarzschild ones in the weak gravitational field. However, in the strong gravitational field, periodic orbits for the particles are investigated by employing a taxonomy. This suggests that the variation of the parameters in RGISBHs can change the taxonomy. This leads to a transition from periodic motion around Schwarzschild black holes to a quasi-periodic motion around these black holes. After that, the epicyclic motions of charged particles around RGISBHs immersed in an external asymptotically uniform magnetic field are taken into account with respect to the observed twin peak quasi-periodic oscillations’ frequencies. The epicyclic motions of charged particles around such black holes in the external magnetic field can give one possible explanation for the 3:2 resonance in three low-mass X-ray binaries. Our results might provide some hints to distinguish RGISBHs from the classical black holes by using periodic orbits and epicyclic motions around the strong gravitational field.
      Citation: Universe
      PubDate: 2022-05-10
      DOI: 10.3390/universe8050278
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 279: Short-Term Consequences of Asteroid Impacts
           into the Ocean: A Portuguese Case Study

    • Authors: Renato H. Morais, Luís F. F. M. Santos, André R. R. Silva, Rui Melicio
      First page: 279
      Abstract: Asteroid impacts are a proven global threat, meaning that any location on Earth might be a subject to their consequences. Such collisions are not likely in any person’s lifetime, but their aftermath could be catastrophic. As Earth’s surface is mostly water, a water impact is more probable than a ground impact, and tsunami waves could pose a significant threat. This study expands the knowledge about asteroid impacts in the ocean and their regional environmental consequences. Three asteroids were assumed to impact the Earth: (1) the Apophis asteroid, a 370 m wide asteroid, (2) a 204 m in diameter asteroid representative of the average impactor on the near-Earth objects, and (3) a 5 km in diameter asteroid. We evaluated the consequences of all impacts for a specific case study, where the chosen impact location was the midpoint between Portugal’s mainland, Azores, and Madeira Islands. The cratering process, generated seismic shaking, overpressure, ejected material, induced thermal radiation, and tsunami waves were assessed, along with the global effects. The overpressure mainly causes structural damage. The thermal radiation can be devastating but has a short reach. The tsunami is undoubtedly the most far-reaching and threatening effect of an asteroid impact in the ocean.
      Citation: Universe
      PubDate: 2022-05-10
      DOI: 10.3390/universe8050279
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 280: Modified Supergravity Phenomenology in
           Gravitational Waves Era

    • Authors: Andrea Addazi, Qingyu Gan
      First page: 280
      Abstract: We discuss phenomenological aspects of modified supergravity (MSG) in gravitational wave (GW) physics. MSG naturally provides double inflation and primordial black holes (PBHs) as cold dark matter. Intriguingly, MSG predicts a large amplification of the scalar and tensor perturbation power spectrum, generating a secondary GW stochastic background which can be tested in space-based interferometers.
      Citation: Universe
      PubDate: 2022-05-12
      DOI: 10.3390/universe8050280
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 281: Field-Theoretical Representation of
           Interactions between Particles: Classical Relativistic Probability-Free
           Kinetic Theory

    • Authors: Anatoly Yu. Zakharov, Victor V. Zubkov
      First page: 281
      Abstract: It was proven that the class of stable interatomic potentials can be represented exactly as a superposition of Yukawa potentials. In this paper, an auxiliary scalar field was introduced to describe the dynamics of a system of neutral particles (atoms) in the framework of classical field theory. In the case of atoms at rest, this field is equivalent to the interatomic potential, but in the dynamic case, it describes the dynamics of a system of atoms interacting through a relativistic classical field. A relativistic Lagrangian is proposed for a system consisting of atoms and an auxiliary scalar field. A complete system of equations for the relativistic dynamics of a system consisting of atoms and an auxiliary field was obtained. A closed kinetic equation was derived for the probability-free microscopic distribution function of atoms. It was shown that the finite mass of the auxiliary field leads to a significant increase in the effect of interaction retardation in the dynamics of a system of interacting particles.
      Citation: Universe
      PubDate: 2022-05-12
      DOI: 10.3390/universe8050281
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 282: Space Weather Effects from Observations by
           Moscow University Cubesat Constellation

    • Authors: Andrey V. Bogomolov, Vitaliy V. Bogomolov, Anatoly F. Iyudin, Valery E. Eremeev, Vladimir V. Kalegaev, Irina N. Myagkova, Vladislav I. Osedlo, Vasiliy L. Petrov, Oleg Y. Peretjat’ko, Mikhail I. Prokhorov, Sergey I. Svertilov, Yury K. Zaiko, Ivan V. Yashin, Vitaliy Y. Prokop’ev, Aleksey S. Styuf, Sergey V. Krasnopeev, Aleksandr P. Papkov
      First page: 282
      Abstract: Moscow State University is developing a project for a multi-satellite constellation intended for the monitoring of space radiation. A number of small satellites of CubeSat format were launched into selected orbits crossing the wide range of magnetic drift shells. The primary scope for the project is the operational monitoring of near-Earth’s radiation environment, i.e., fluxes of electrons and protons of Earth’s radiation belts and energetic particles of solar and galactic origin. To date, there are four CubeSat satellites operating in near-Earth orbits, which deliver scientific and telemetric data. Thus, for the first time, a unique multi-satellite constellation has been implemented, which makes it possible to simultaneously measure the particle and quantum fluxes at different areas in the near-Earth space using the same type of instruments. A special compact detector of gamma quanta and energetic charged particles (electrons and protons) DeCoR has been developed to carry out radiation monitoring by CubeSats. With their help, observations of various effects of space weather have been made. These effects include a variety of electron fluxes in the outer belt during geomagnetic activity in late November–early December 2021, filling of polar caps by solar energetic particles accelerated in flares occurring in late October–early November, and the existence of stable electron fluxes near the geomagnetic equator.
      Citation: Universe
      PubDate: 2022-05-12
      DOI: 10.3390/universe8050282
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 283: Extended Gravity Constraints at Different

    • Authors: Stanislav Alexeyev, Vyacheslav Prokopov
      First page: 283
      Abstract: We review a set of the possible ways to constrain extended gravity models at Galaxy clusters scales (the regime of dark energy explanations and comparison with ΛCDM), for black hole shadows, gravitational wave astronomy, binary pulsars, the Solar system and a Large Hadron Collider (consequences for high-energy physics at TeV scale). The key idea is that modern experimental and observational precise data provide us with the chance to go beyond general relativity.
      Citation: Universe
      PubDate: 2022-05-15
      DOI: 10.3390/universe8050283
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 284: A Short Review on the Latest Neutrinos Mass
           and Number Constraints from Cosmological Observables

    • Authors: Ziad Sakr
      First page: 284
      Abstract: We review the neutrino science, focusing on its impact on cosmology along with the latest constraints on its mass and number of species. We also discuss its status as a possible solution to some of the recent cosmological tensions, such as the Hubble constant or the matter fluctuation parameter. We end by showing forecasts from next-generation planned or candidate surveys, highlighting their constraining power, alone or in combination, but also the limitations in determining neutrino mass distribution among its species.
      Citation: Universe
      PubDate: 2022-05-16
      DOI: 10.3390/universe8050284
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 285: Binary X-ray Sources in Massive
           Brans–Dicke Gravity

    • Authors: Grigoris Panotopoulos, Ángel Rincón, Ilídio Lopes
      First page: 285
      Abstract: This study focuses on the X-ray emission of low-mass black hole binaries in massive Brans–Dicke gravity. First, we compute the accretion disk with the well-known Shakura–Sunyaev model for an optically thick, cool, and geometrically thin disk. Moreover, we assume that the gravitational field generated by the stellar-mass black hole is an analogue of the Schwarzschild space-time of Einstein’s theory in massive Brans–Dicke gravity. We compute the most relevant quantities of interest, i.e., (i) the radial velocity, (ii) the energy and surface density, and (iii) the pressure as a function entirely of the radial coordinate. We also compute the soft spectral component of the X-ray emission produced by the disk. Furthermore, we investigate in detail how the mass of the scalar field modifies the properties of the binary as described by the more standard Schwarzschild solution.
      Citation: Universe
      PubDate: 2022-05-19
      DOI: 10.3390/universe8050285
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 286: A Short Overview on Low Mass Scalars at
           Future Lepton Colliders

    • Authors: Tania Robens
      First page: 286
      Abstract: In this manuscript, I give a short summary on scenarios with new physics scalars that could be investigated at future e+e− colliders. I concentrate on cases where at least one of the additional scalars has a mass below 125 GeV, and discuss both models where this could be realized, as well as studies which focus on such scenarios. This work is based on several overview talks I recently gave at the CEPC workshop, FCC week and ECFA future collider workshop, as well as a Snowmass White Paper.
      Citation: Universe
      PubDate: 2022-05-20
      DOI: 10.3390/universe8050286
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 287: GeV Proton Detection in the 8 November 2000
           Solar Event

    • Authors: Ruiguang Wang, Zhongqiang Yu, Yuqian Ma, Linkai Ding, Qingqi Zhu, Zhiguo Yao, Xinhua Ma, Yupeng Xu, Changgen Yang
      First page: 287
      Abstract: In this study, we analyze the L3 precision muon spectrometer data from November 2000. The results showed that a 4.7σmuon excess appeared at a time coincident with the solar flare of 8 November 2000. This muon excess corresponded to primary protons above 40 GeV, coming from a sky cell of solid angle 0.048 sr. The probability of being a background fluctuation was estimated to be about 0.1%. It is interesting and noteworthy that an M-class solar flare may also accelerate solar protons to such high energies.
      Citation: Universe
      PubDate: 2022-05-20
      DOI: 10.3390/universe8050287
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 288: Quantum Current Algebra in Action:
           Linearization, Integrability of Classical and Factorization of Quantum
           Nonlinear Dynamical Systems

    • Authors: Anatolij K. Prykarpatski
      First page: 288
      Abstract: This review is devoted to the universal algebraic and geometric properties of the non-relativistic quantum current algebra symmetry and to their representations subject to applications in describing geometrical and analytical properties of quantum and classical integrable Hamiltonian systems of theoretical and mathematical physics. The Fock space, the non-relativistic quantum current algebra symmetry and its cyclic representations on separable Hilbert spaces are reviewed and described in detail. The unitary current algebra family of operators and generating functional equations are described. A generating functional method to constructing irreducible current algebra representations is reviewed, and the ergodicity of the corresponding representation Hilbert space measure is mentioned. The algebraic properties of the so called coherent states are also reviewed, generated by cyclic representations of the Heisenberg algebra on Hilbert spaces. Unbelievable and impressive applications of coherent states to the theory of nonlinear dynamical systems on Hilbert spaces are described, along with their linearization and integrability. Moreover, we present a further development of these results within the modern Lie-algebraic approach to nonlinear dynamical systems on Poissonian functional manifolds, which proved to be both unexpected and important for the classification of integrable Hamiltonian flows on Hilbert spaces. The quantum current Lie algebra symmetry properties and their functional representations, interpreted as a universal algebraic structure of symmetries of completely integrable nonlinear dynamical systems of theoretical and mathematical physics on functional manifolds, are analyzed in detail. Based on the current algebra symmetry structure and their functional representations, an effective integrability criterion is formulated for a wide class of completely integrable Hamiltonian systems on functional manifolds. The related algebraic structure of the Poissonian operators and an effective algorithm of their analytical construction are described. The current algebra representations in separable Hilbert spaces and the factorized structure of quantum integrable many-particle Hamiltonian systems are reviewed. The related current algebra-based Hamiltonian reconstruction of the many-particle oscillatory and Calogero–Moser–Sutherland quantum models are reviewed and discussed in detail. The related quasi-classical quantum current algebra density representations and the collective variable approach in equilibrium statistical physics are reviewed. In addition, the classical Wigner type current algebra representation and its application to non-equilibrium classical statistical mechanics are described, and the construction of the Lie–Poisson structure on the phase space of the infinite hierarchy of distribution functions is presented. The related Boltzmann–Bogolubov type kinetic equation for the generating functional of many-particle distribution functions is constructed, and the invariant reduction scheme, compatible with imposed correlation functions constraints, is suggested and analyzed in detail. We also review current algebra functional representations and their geometric structure subject to the analytical description of quasi-stationary hydrodynamic flows and their magneto-hydrodynamic generalizations. A unified geometric description of the ideal idiabatic liquid dynamics is presented, and its Hamiltonian structure is analyzed. A special chapter of the review is devoted to recent results on the description of modified current Lie algebra symmetries on torus and their Lie-algebraic structures, related to integrable so-called heavenly type spatially many-dimensional dynamical systems on functional manifolds.
      Citation: Universe
      PubDate: 2022-05-20
      DOI: 10.3390/universe8050288
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 289: Multi-Messenger Constraints on the Hubble
           Constant Through Combination of Gravitational Waves, Gamma-Ray Bursts and
           Kilonovae from Neutron Star Mergers

    • Authors: Mattia Bulla, Michael W. Coughlin, Suhail Dhawan, Tim Dietrich
      First page: 289
      Abstract: The simultaneous detection of gravitational waves and light from the binary neutron star merger GW170817 led to independent measurements of distance and redshift, providing a direct estimate of the Hubble constant H0 that does not rely on a cosmic distance ladder, nor assumes a specific cosmological model. By using gravitational waves as “standard sirens”, this approach holds promise to arbitrate the existing tension between the H0 value inferred from the cosmic microwave background and those obtained from local measurements. However, the known degeneracy in the gravitational-wave analysis between distance and inclination of the source led to a H0 value from GW170817 that was not precise enough to resolve the existing tension. In this review, we summarize recent works exploiting the viewing-angle dependence of the electromagnetic signal, namely the associated short gamma-ray burst and kilonova, to constrain the system inclination and improve on H0. We outline the key ingredients of the different methods, summarize the results obtained in the aftermath of GW170817 and discuss the possible systematics introduced by each of these methods.
      Citation: Universe
      PubDate: 2022-05-21
      DOI: 10.3390/universe8050289
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 290: Gasflows in Barred Galaxies with Big Orbital
           Loops—A Comparative Study of Two Hydrocodes

    • Authors: Stavros Pastras, Panos A. Patsis, E. Athanassoula
      First page: 290
      Abstract: We study the flow of gas in a barred-galaxy model, in which a considerable part of the underlying stable periodic orbits have loops where, close to the ends of the bar, several orbital families coexist and chaos dominates. Such conditions are typically encountered in a zone between the 4:1 resonance and corotation. The purpose of our study is to understand the gaseous flow in the aforementioned environment and trace the morphology of the shocks that form. We use two conceptually different hydrodynamic schemes for our calculations, namely, the mesh-free Lagrangian SPH method and the adaptive mesh refinement code RAMSES. This allows us to compare responses by means of the two algorithms. We find that the big loops of the orbits, mainly belonging to the x1 stable periodic orbits, do not help the shock loci to approach corotation. They deviate away from the regions occupied by the loops, bypass them and form extensions at an angle with the straight-line shocks. Roughly at the distance from the center at which we start to observe the big loops, we find characteristic “tails” of dense gas streaming towards the straight-line shocks. The two codes give complementary information for understanding the hydrodynamics of the models.
      Citation: Universe
      PubDate: 2022-05-22
      DOI: 10.3390/universe8050290
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 291: Quantum Capacity and Vacuum Compressibility
           of Spacetime: Thermal Fields

    • Authors: Hing-Tong Cho, Jen-Tsung Hsiang, Bei-Lok Hu
      First page: 291
      Abstract: An important yet perplexing result from work in the 1990s and 2000s is the near-unity value of the ratio of fluctuations in the vacuum energy density of quantum fields to the mean in a collection of generic spacetimes. This was carried out by way of calculating the noise kernels which are the correlators of the stress-energy tensor of quantum fields. In this paper, we revisit this issue via a quantum thermodynamics approach, by calculating two quintessential thermodynamic quantities: the heat capacity and the quantum compressibility of some model geometries filled with a quantum field at high and low temperatures. This is because heat capacity at constant volume gives a measure of the fluctuations of the energy density to the mean. When this ratio approaches or exceeds unity, the validity of the canonical distribution is called into question. Likewise, a system’s compressibility at constant pressure is a criterion for the validity of grand canonical ensemble. We derive the free energy density and, from it, obtain the expressions for these two thermodynamic quantities for thermal and quantum fields in 2d Casimir space, 2d Einstein cylinder and 4d (S1×S3 ) Einstein universe. To examine the dependence on the dimensionality of space, for completeness, we have also derived these thermodynamic quantities for the Einstein universes with even-spatial dimensions: S1×S2 and S1×S4. With this array of spacetimes we can investigate the thermodynamic stability of quantum matter fields in them and make some qualitative observations on the compatibility condition for the co-existence between quantum fields and spacetimes, a fundamental issue in the quantum and gravitation conundrum.
      Citation: Universe
      PubDate: 2022-05-21
      DOI: 10.3390/universe8050291
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 292: Bounce Universe with Finite-Time Singularity

    • Authors: Sergei D. Odintsov, Tanmoy Paul
      First page: 292
      Abstract: This work explains how the presence of a Type-IV singularity (a mild singularity) can influence the dynamics of a bouncing universe. In particular, we examine the bounce cosmology that appears with a Type-IV singularity in the context of a ghost-free Gauss–Bonnet theory of gravity. Depending on the time of occurrence of the Type-IV singularity, three different cases may arise—when the singularity occurs before the bounce, after the bounce, or at the instant of the bounce. However, in all of these cases, we find that in the case when the singularity “globally” affects the spacetime, the scalar power spectrum becomes red-tilted, and the tensor-to-scalar ratio is too large to be consistent with the observational data. Based on these findings, we investigate a different bouncing scenario which also appears with a Type-IV singularity, and wherein the singularity affects the spacetime “locally” around the time when it occurs. As a result, and unlike the previous scenario, the perturbation modes in the second bouncing scenario are likely to be generated far away from the bounce in the deep contracting phase. This finally results in the simultaneous compatibility of the observable quantities with the Planck data and ensures the viability of the bounce model where the Type-IV singularity has local effects on the spacetime around the time of the singularity.
      Citation: Universe
      PubDate: 2022-05-23
      DOI: 10.3390/universe8050292
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 293: Positive Energy and Non-SUSY Flows in ISO(7)
           Gauged Supergravity

    • Authors: Giuseppe Dibitetto
      First page: 293
      Abstract: We consider maximal gauged supergravity in 4D with the ISO(7) gauge group, which arises from a consistent truncation of massive IIA supergravity on a six-sphere. Within its G2-invariant sector, the theory is known to possess a supersymmetric AdS extremum, as well as two non-supersymmetric ones. In this context, we provide a first-order formulation of the theory by making use of the Hamilton–Jacobi (HJ) formalism. This allows us to derive a positive energy theorem for both non-supersymmetric extrema. Subsequently, we also find novel non-supersymmetric domain walls (DWs) interpolating between the supersymmetric extremum and each of the other two. Finally, we discuss a perturbative HJ technique that may be used in order to solve for curved DW geometries.
      Citation: Universe
      PubDate: 2022-05-23
      DOI: 10.3390/universe8050293
      Issue No: Vol. 8, No. 5 (2022)
  • Universe, Vol. 8, Pages 196: Search for Muon-to-Electron Conversion with
           the COMET Experiment

    • Authors: Manabu Moritsu
      First page: 196
      Abstract: Charged Lepton Flavor Violation is expected to be one of the most powerful tools to reveal physics beyond the Standard Model. The COMET experiment aims to search for the neutrinoless coherent transition of a muon into an electron in the field of a nucleus. Muon-to-electron conversion has never been observed, and can be, and would be, clear evidence of new physics if discovered. The experimental sensitivity of this process, defined as the ratio of the muon-to-electron conversion rate to the total muon capture rate, is expected to be significantly improved by a factor of 100 to 10,000 in the coming decade. The COMET experiment will take place at J-PARC with single event sensitivities of the orders of 10−15 and 10−17 in Phase-I and Phase-II, respectively. The ambitious goal of the COMET experiment is achieved by realizing a high-quality pulsed beam and an unprecedentedly powerful muon source together with an excellent detector apparatus that can tolerate a severe radiation environment. The construction of a new beam line, superconducting magnets, detectors and electronics is in progress towards the forthcoming Phase-I experiment. We present the experimental methods, sensitivity and backgrounds along with recent status and prospects.
      Citation: Universe
      PubDate: 2022-03-22
      DOI: 10.3390/universe8040196
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 197: Analogue Metric in a Black-Bounce Background

    • Authors: Kunal Pal, Kuntal Pal, Tapobrata Sarkar
      First page: 197
      Abstract: The conventional approach of embedding an effective acoustic metric for sound motion in a background flat Minkowski space-time has recently been extended to incorporate more general curved background metrics, which might contain a black hole. Though the observational aspects of these kinds of acoustics horizons, including the sonic shadow structure and quasi normal modes, have received significant attention in the literature, there is room left for discussions about embedding more general classes of curved background space-times without optical horizons. Here, we propose and study a new class of acoustic metrics that is embedded in a black-bounce space-time, thereby giving a suitable tuneable system to understand possible observational effects of the presence or absence of acoustic horizons. After showing that the metric can represent five types of different effective backgrounds for sound motion, including a novel “acoustic wormhole–optical wormhole” branch, we discuss how the distinctive features of sonic shadows can appear even in the absence of any acoustic horizon due to the wormhole throat present in the acoustic metric.
      Citation: Universe
      PubDate: 2022-03-22
      DOI: 10.3390/universe8040197
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 198: Editorial for the Special Issue
           “Asymptotic Safety in Quantum Gravity”

    • Authors: Antonio D. Pereira
      First page: 198
      Abstract: Asymptotically safe quantum gravity (ASQG) attempts to provide a standard quantum-field theoretic description of quantum spacetime across arbitrarily small length scales [...]
      Citation: Universe
      PubDate: 2022-03-23
      DOI: 10.3390/universe8040198
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 199: Hyperbolic Inflation in the Jordan Frame

    • Authors: Andronikos Paliathanasis
      First page: 199
      Abstract: We consider a multi-scalar field model in the Jordan frame, which can be seen as a two-scalar field model where the Brans–Dicke field interacts in the kinetic part with the second scalar field. This theory under a conformal transformation reduces to the hyperbolic inflation. We show that scaling solutions and the de Sitter universe are provided by the theory. In the study of asymptotic dynamics, we determine an attractor where all the fluid sources contribute in the cosmological fluid. This attractor is always a spiral, and it can be seen as the analogue of the hyperbolic inflation in the Jordan frame.
      Citation: Universe
      PubDate: 2022-03-23
      DOI: 10.3390/universe8040199
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 200: D-Branes in Para-Hermitian Geometries

    • Authors: Vincenzo Emilio Marotta, Richard J. Szabo
      First page: 200
      Abstract: We introduce T-duality invariant versions of D-branes in doubled geometry using a global covariant framework based on para-Hermitian geometry and metric algebroids. We define D-branes as conformal boundary conditions for the open string version of the Born sigma-model, where they are given by maximally isotropic vector bundles which do not generally admit the standard geometric picture in terms of submanifolds. When reduced to the conventional sigma-model description of a physical string background as the leaf space of a foliated para-Hermitian manifold, integrable branes yield D-branes as leaves of foliations which are interpreted as Dirac structures on the physical spacetime. We define a notion of generalised para-complex D-brane, which realises our D-branes as para-complex versions of topological A/B-branes. We illustrate how our formalism recovers standard D-branes in the explicit example of reductions from doubled nilmanifolds.
      Citation: Universe
      PubDate: 2022-03-23
      DOI: 10.3390/universe8040200
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 201: Modified Equations of State for Dark Energy
           and Observational Limitations

    • Authors: German S. Sharov, Vasily E. Myachin
      First page: 201
      Abstract: Cosmological models with variable and modified equations of state for dark energy are confronted with observational data, including Type Ia supernovae, Hubble parameter data H(z) from different sources, and observational manifestations of cosmic microwave background radiation (CMB). We consider scenarios generalizing the ΛCDM, wCDM, and Chevallier–Polarski–Linder (CPL) models with nonzero curvature and compare their predictions. The most successful model with the dark energy equation of state w=w0+w1(1−a2)/2 was studied in detail. These models are interesting in possibly alleviating the Hubble constant H0 tension, but they achieved a modest success in this direction with the considered observational data.
      Citation: Universe
      PubDate: 2022-03-24
      DOI: 10.3390/universe8040201
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 202: Neutrino Dynamics in a Quantum-Corrected
           Schwarzschild Spacetime

    • Authors: Fabrizio Illuminati, Gaetano Lambiase, Luciano Petruzziello
      First page: 202
      Abstract: We study neutrino propagation in a curved spacetime background described by the Schwarzschild solution with the addition of quantum corrections evaluated in the framework of perturbative quantum gravity at lowest order. In particular, we investigate neutrino oscillations and decoherence within the Gaussian wave packet description, finding that quantum gravity corrections significantly affect the intrinsic features of mixed particles and induce potentially measurable physical effects.
      Citation: Universe
      PubDate: 2022-03-24
      DOI: 10.3390/universe8040202
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 203: Why Is the Mean Anomaly at Epoch Not Used in
           Tests of Non-Newtonian Gravity'

    • Authors: Lorenzo Iorio
      First page: 203
      Abstract: The mean anomaly at epoch η is one of the standard six Keplerian orbital elements in terms of which the motion of the two-body problem is parameterized. Along with the argument of pericenter ω, η experiences long-term rates of change induced, among other things, by general relativity and several modified models of gravity. Thus, in principle, it may be fruitfully adopted together with ω in several tests of post-Newtonian gravity performed with astronomical and astrophysical binary systems. This would allow us to enhance the gravitational signature we are interested in and to disentangle some competing disturbing effects acting as sources of systematic bias. Nonetheless, for some reasons unknown to the present author, η has never been used so far by astronomers in actual data reductions. This note aims to raise interest in the community about the possible practical use of such an orbital element or, at least, to induce experts in astronomical data processing to explicitly make clear if it is not possible to use η for testing gravitational models and, if this is the case, why.
      Citation: Universe
      PubDate: 2022-03-24
      DOI: 10.3390/universe8040203
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 204: On the Inner Horizon Instability of
           Non-Singular Black Holes

    • Authors: Francesco Di Filippo, Raúl Carballo-Rubio, Stefano Liberati, Costantino Pacilio, Matt Visser
      First page: 204
      Abstract: Regular black holes represent a conservative model in which the classical singularity is replaced by a non-singular core without necessarily modifying the spacetime outside the trapping horizon. Given the possible lack of phenomenological signatures, it is crucial to study the consistency of the model. In this short work, we review the physical mechanism leading to the instability of the central core, arguing that that non-perturbative backreation is non-negligible and must be taken into account to provide a meaningful description of physical black holes.
      Citation: Universe
      PubDate: 2022-03-25
      DOI: 10.3390/universe8040204
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 205: Towards an Acoustic Geometry in Slightly
           Viscous Fluids

    • Authors: Mayank Pathak, Parthasarathi Majumdar
      First page: 205
      Abstract: We explore the behaviour of barotropic and irrotational fluids with a small viscosity under the effect of first-order acoustic perturbations. We discuss, following the extant literature, the difficulties in gleaning an acoustic geometry in the presence of viscosity. In order to obviate various technical encumbrances, when viscosity is present, for an extraction of a possible acoustic geometry, we adopted a method of double perturbations, whereby dynamical quantities such as the velocity field and potential undergo a perturbation both in viscosity and in an external acoustic stimulus. The resulting perturbation equations yield a solution which can be interpreted in terms of a generalised acoustic geometry, over and above the one known for inviscid fluids.
      Citation: Universe
      PubDate: 2022-03-25
      DOI: 10.3390/universe8040205
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 206: RR Lyrae Variables as Tracers of the Galactic
           Bulge Kinematic Structure

    • Authors: Andrea M. Kunder
      First page: 206
      Abstract: RR Lyrae stars are recognized as some of the oldest stars in the Universe. In addition, they are some of the few old celestial objects for which distances can be reliably inferred. As such, these stars are excellent tracers of the oldest structures that exist in the inner Galaxy. Although the inner Galaxy is where the oldest structures in the Milky Way are thought to be hidden, it is also a region notoriously difficult to study due to high extinction and crowding. Here, I will summarize how RR Lyrae stars have been used to obtain a more complete picture of the inner Galaxy. In particular, recently, a large sample of RR Lyrae star motions through space have been obtained and compared to younger, more metal-rich stars in the bulge/bar. It is seen that the inner Galaxy RR Lyrae star kinematics are complicated by a mix of a variety of Galactic components. After isolating only those RR Lyrae stars that are confined to the bulge, a subsample of these stars have slower rotation and are less barred than the dominant bar/bulge. Curiously, there is no discernible metallicity [Fe/H] difference between these two subsamples. Old, metal-poor stars in the inner Galaxy need to be properly accounted for when discussing processes that gave rise to the formation of the inner Galaxy and the Galactic bar/bulge.
      Citation: Universe
      PubDate: 2022-03-25
      DOI: 10.3390/universe8040206
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 207: Are Quantum-Classical Hybrids Compatible with
           Ontological Cellular Automata'

    • Authors: Hans-Thomas Elze
      First page: 207
      Abstract: Based on the concept of ontological states and their dynamical evolution by permutations, as assumed in the Cellular Automaton Interpretation (CAI) of quantum mechanics, we address the issue of whether quantum-classical hybrids can be described consistently in this framework. We consider chains of `classical’ two-state Ising spins and their discrete deterministic dynamics as an ontological model with an unitary evolution operator generated by pair-exchange interactions. A simple error mechanism is identified, which turns them into quantum mechanical objects: chains of qubits. Consequently, an interaction between a quantum mechanical and a `classical’ chain can be introduced and its consequences for this quantum-classical hybrid can be studied. We found that such hybrid character of composites, generally, does not persist under interactions and, therefore, cannot be upheld consistently, or even as a fundamental notion à la Kopenhagen interpretation, within CAI.
      Citation: Universe
      PubDate: 2022-03-26
      DOI: 10.3390/universe8040207
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 208: How-to Compute EPRL Spin Foam Amplitudes

    • Authors: Pietro Donà, Pietropaolo Frisoni
      First page: 208
      Abstract: Spin foam theory is a concrete framework for quantum gravity where numerical calculations of transition amplitudes are possible. Recently, the field became very active, but the entry barrier is steep, mainly because of its unusual language and notions scattered around the literature. This paper is a pedagogical guide to spin foam transition amplitude calculations. We show how to write an EPRL-FK transition amplitude, from the definition of the 2-complex to its numerical implementation using sl2cfoam-next. We guide the reader using an explicit example balancing mathematical rigor with a practical approach. We discuss the advantages and disadvantages of our strategy and provide a novel look at a recently proposed approximation scheme.
      Citation: Universe
      PubDate: 2022-03-26
      DOI: 10.3390/universe8040208
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 209: Kelvin–Helmholtz Waves on the
           Magnetopause at the Lunar Distances under Southward IMF: ARTEMIS

    • Authors: Yue Zhou, Jianyong Lu, Ming Wang
      First page: 209
      Abstract: The Kelvin–Helmholtz (KH) instability, a common phenomenon widely observed at the magnetopause, plays an important role in plasma transport while reconnection at low latitude is less efficient during the northward interplanetary magnetic field (IMF). In this study, we analyze the magnetic field and plasma observations obtained by the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon’s Interaction with the Sun (ARTEMIS) spacecraft located near the lunar orbit and find KH waves under the southward IMF at the lunar-orbit magnetopause. We also calculate the dominant period, phase velocity, and wavelength of the KH waves and further compare this event with the KH waves seen at the flank magnetopause under the southward IMF, which indicates that the wavelength increases as the distance from the subsolar point increases. The observations also show that the KH waves at lunar distance under the southward IMF are characterized by irregularity and intermittence.
      Citation: Universe
      PubDate: 2022-03-26
      DOI: 10.3390/universe8040209
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 210: Equatorial and Polar Quasinormal Modes and
           Quasiperiodic Oscillations of Quantum Deformed Kerr Black Hole

    • Authors: Kimet Jusufi, Mustapha Azreg-Aïnou, Mubasher Jamil, Qiang Wu
      First page: 210
      Abstract: In this paper, we focus on the relation between quasinormal modes (QNMs) and a rotating black hole shadow. As a specific example, we consider the quantum deformed Kerr black hole obtained via Newman–Janis–Azreg-Aïnou algorithm. In particular, using the geometric-optics correspondence between the parameters of a QNMs and the conserved quantities along geodesics, we show that, in the eikonal limit, the real part of QNMs is related to the Keplerian frequency for equatorial orbits. To this end, we explore the typical shadow radius for the viewing angles, θ0=π/2, and obtained an interesting relation in the case of viewing angle θ0=0 (or equivalently θ0=π). Furthermore we have computed the corresponding equatorial and polar modes and the thermodynamical stability of the quantum deformed Kerr black hole. We also investigate other astrophysical applications such as the quasiperiodic oscillations and the motion of S2 star to constrain the quantum deforming parameter.
      Citation: Universe
      PubDate: 2022-03-26
      DOI: 10.3390/universe8040210
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 211: Tidal Quality of the Hot Jupiter WASP-12b

    • Authors: Michael Efroimsky, Valeri V. Makarov
      First page: 211
      Abstract: WASP-12b stands out among the planets of its class of hot Jupiters because of the observed fast orbital decay attributed to tidal dissipation. The measured rate of the orbital period change is P⋅orb=−29±3ms/yr=(9.2±1.0)×10−10s/s. In the literature heretofore, all attempts to explain this high rate were based on the assumption that the orbital evolution is dominated by the tides in the star. Since the modified tidal quality factor in yellow dwarfs is insufficient to warrant such a decay rate, a hypothesis was put forward that the star may actually be a subgiant. Using the latest data from the Gaia mission, we deduce that WASP-12 at 1.36M☼ is an evolving dwarf at an early stage of post-turn-off evolution that has not yet depleted hydrogen in its core. Its unremarkable position in the color-magnitude diagram and the existence of close planets orbiting red giants of similar mass contradict the hypothesis of an abrupt boost of tidal quality due to structural internal changes. On the other hand, the previous research neglected the tidal dissipation in the planet, assuming it to be negligible due to the likely synchronisation of its rotation and a presumed high quality factor. We critically reassess this assumption in the light of recent astrometric results for Jupiter and Saturn. Assuming that the structure of WASP-12b is similar to that of our Jupiter and Saturn, we find that the observed orbital decay is well explained by the tides in the planet. The estimated value of the planet’s modified quality factor coincides almost precisely with that of our Jupiter.
      Citation: Universe
      PubDate: 2022-03-26
      DOI: 10.3390/universe8040211
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 212: Dust in Clusters of Galaxies

    • Authors: Yuri A. Shchekinov, Biman B. Nath, Evgenii O. Vasiliev
      First page: 212
      Abstract: The presence of dust in the intracluster medium (ICM) has been a long-standing problem that is still awaiting elucidation. Direct observational diagnostics are rather challenging (though not impossible) either because of a sparse distribution of dust in the intracluster space that makes extinction measurements difficult or because of a low surface brightness of infrared emission from dust. Complex indirect approaches are currently available that can overcome uncertainties and provide a reasonable understanding of the basic regulations of the physical state of dust in the ICM. Contrary to the common opinion that the hot ICM does not allow dust to survive and manifest, many sparse observational data either directly point out that dust exists in the intracluster space or its presence is consistent with the data. Highly divergent data in direct evidence and highly uncertain indirect indicators are often connected either with dust fragility in a hot environment, the possible compactness of spatial (clumpy) dust distribution in the ICM, or dynamical features of dust transport. The source of dust is obviously connected with galaxies, and it turns out that in most cases, dust is carried from galaxies into the ICM while being thermally and dynamically shielded against the hostile influence of high-energy ions. In this review, we briefly discuss related issues from observational and theoretical points of view, including the transport of dust into the ICM, and the associated destructive and protective mechanisms and their characteristic time scales.
      Citation: Universe
      PubDate: 2022-03-26
      DOI: 10.3390/universe8040212
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 213: The Scale Invariant Vacuum Paradigm: Main
           Results and Current Progress

    • Authors: Vesselin G. Gueorguiev, Andre Maeder
      First page: 213
      Abstract: We present a summary of the main results within the Scale Invariant Vacuum (SIV) paradigm as related to the Weyl Integrable Geometry (WIG) as an extension to the standard Einstein General Relativity (EGR). After a brief review of the mathematical framework, we will highlight the main results related to inflation within the SIV, the growth of the density fluctuations, and the application of the SIV to scale-invariant dynamics of galaxies, MOND, dark matter, and the dwarf spheroidals. The possible connection between the weak-field SIV equations and the notion of un-proper time parametrization within the reparametrization paradigm is also discussed.
      Citation: Universe
      PubDate: 2022-03-27
      DOI: 10.3390/universe8040213
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 214: The Principle of Maximum Entropy and the
           Distribution of Mass in Galaxies

    • Authors: Jorge Sánchez Almeida
      First page: 214
      Abstract: We do not have a final answer to the question of why galaxies choose a particular internal mass distribution. Here we examine whether the distribution is set by thermodynamic equilibrium (TE). Traditionally, TE is discarded for a number of reasons including the inefficiency of two-body collisions to thermalize the mass distribution in a Hubble time, and the fact that the mass distribution maximizing the classical Boltzmann–Gibbs entropy is unphysical. These arguments are questionable. In particular, when the Tsallis entropy that describes self-gravitating systems is used to define TE, the mass distributions that result (i.e., the polytropes) are physically sensible. This work spells out this and other arguments for TE and presents the polytropes and their properties. It puts forward empirical evidence for the mass distribution observed in galaxies to be consistent with polytropes. It compares polytropes with Sérsic functions and it shows how the DM halos resulting from cosmological numerical simulations become polytropes when efficient collisions are allowed. It also discusses pathways to thermalization bypassing two-body collisions. It finally outlines future developments including deciphering whether or not DM particles collide efficiently.
      Citation: Universe
      PubDate: 2022-03-28
      DOI: 10.3390/universe8040214
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 215: A Matrix Model of Four-Dimensional
           Noncommutative Gravity

    • Authors: George Manolakos, Pantelis Manousselis, Danai Roumelioti, Stelios Stefas, George Zoupanos
      First page: 215
      Abstract: In this review, we revisit our latest works regarding the description of the gravitational interaction on noncommutative spaces as matrix models. Specifically, inspired by the gauge-theoretic approach of (ordinary) gravity, we make use of the suggested methodology, modified appropriately for the noncommutative framework, of the well-established formulation of gauge theories on them. Making use of a covariant four-dimensional fuzzy space, we formulate the gauge theory with an extended gauge group due to noncommutativity. In turn, in order to decrease the amount of symmetry we employ a symmetry breaking and result with an action which describes a theory that is a minimal noncommutative extension of the original.
      Citation: Universe
      PubDate: 2022-03-28
      DOI: 10.3390/universe8040215
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 216: Challenges and Requirements in High-Precision
           Nuclear Astrophysics Experiments

    • Authors: György Gyürky
      First page: 216
      Abstract: In the 21th century astronomical observations, as well as astrophysical models, have become impressively precise. For a better understanding of the processes in stellar interiors, the nuclear physics of astrophysical relevance—known as nuclear astrophysics—must aim for similar precision, as such precision is not reached yet in many cases. This concerns both nuclear theory and experiment. In this paper, nuclear astrophysics experiments are put in focus. Through the example of various parameters playing a role in nuclear reaction studies, the difficulties of reaching high precision and the possible solutions are discussed.
      Citation: Universe
      PubDate: 2022-03-28
      DOI: 10.3390/universe8040216
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 217: Linear Superposition as a Core Theorem of
           Quantum Empiricism

    • Authors: Brezhnev
      First page: 217
      Abstract: Clarifying the nature of the quantum state Ψ⟩ is at the root of the problems with insight into counter-intuitive quantum postulates. We provide a direct—and math-axiom free—empirical derivation of this object as an element of a vector space. Establishing the linearity of this structure—quantum superposition—is based on a set-theoretic creation of ensemble formations and invokes the following three principia: (I) quantum statics, (II) doctrine of the number in the physical theory, and (III) mathematization of matching the two observations with each other (quantum covariance). All of the constructs rest upon a formalization of the minimal experimental entity—the registered micro-event, detector click. This is sufficient for producing the C-numbers, axioms of linear vector space (superposition principle), statistical mixtures of states, eigenstates and their spectra, and non-commutativity of observables. No use is required of the spatio-temporal concepts. As a result, the foundations of theory are liberated to a significant extent from the issues associated with physical interpretations, philosophical exegeses, and mathematical reconstruction of the entire quantum edifice.
      Citation: Universe
      PubDate: 2022-03-28
      DOI: 10.3390/universe8040217
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 218: Radiation of High-Energy Gamma Quanta by
           Ultrarelativistic Electrons on Nuclei in Strong X-ray Fields

    • Authors: Sergei Roshchupkin, Alexander Dubov, Stanislav Starodub
      First page: 218
      Abstract: The possibility of radiation of high-energy gamma quanta with energies of the order of 100 GeV by ultrarelativistic electrons on nuclei in strong X-ray fields with intensities up to ∼1027Wcm−2 was theoretically studied. It is shown that this effect can be realized under special experimental conditions in the process of resonant spontaneous bremsstrahlung radiation of ultrarelativistic electrons on nuclei in an external electromagnetic field. These special experimental conditions determine the characteristic energy of the electrons. This characteristic energy should be significantly less than the energy of the initial electrons. Under these conditions, spontaneous gamma quanta are emitted in a narrow cone with energies close to the energy of the initial electrons. Moreover, the resonant differential cross-sections of such processes can exceed the corresponding differential cross-section without an external field by twenty orders of magnitude. The results obtained can explain the occurrence of high-energy gamma quanta near pulsars and magnetars.
      Citation: Universe
      PubDate: 2022-03-29
      DOI: 10.3390/universe8040218
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 219: Technological Novelties of Ground-Based Very
           High Energy Gamma-Ray Astrophysics with the Imaging Atmospheric Cherenkov

    • Authors: Razmik Mirzoyan
      First page: 219
      Abstract: In the past three decades, the ground-based technique of imaging atmospheric Cherenkov telescopes has established itself as a powerful discipline in science. Approximately 250 sources of very high gamma rays of both galactic and extra-galactic origin have been discovered largely due to this technique. The study of these sources is providing clues to many basic questions in astrophysics, astro-particle physics, physics of cosmic rays and cosmology. The currently operational generation of telescopes offer a solid performance. Further improvements of this technique led to the next-generation large instrument known as the Cherenkov Telescope Array. In its final configuration, the sensitivity of CTA will be several times higher than that of the currently best instruments VERITAS, H.E.S.S., and MAGIC. This article is devoted to outlining the technological developments that shaped this technique and led to today’s success.
      Citation: Universe
      PubDate: 2022-03-29
      DOI: 10.3390/universe8040219
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 220: Insights into AGB Nucleosynthesis Thanks to
           Spectroscopic Abundance Measurements in Intrinsic and Extrinsic Stars

    • Authors: Sophie Van Eck, Shreeya Shetye, Lionel Siess
      First page: 220
      Abstract: The foundations of stellar nucleosynthesis have been established more than 70 years ago. Since then, much progress has been made, both on the theoretical side, with stellar evolution and nucleosynthesis models of increasing complexity, using more and more accurate nuclear data, and on the observational side, with the number of analyzed stars growing tremendously. In between, the complex machinery of abundance determination has been refined, taking into account model atmospheres of non-solar chemical composition, three-dimensional, non-LTE (non-local thermodynamic equilibrium) effects, and a growing number of atomic and molecular data. Neutron-capture nucleosynthesis processes, and in particular the s-process, have been scrutinized in various types of evolved stars, among which asymptotic giant branch stars, carbon-enhanced metal-poor stars and post-AGB stars. We review here some of the successes of the comparison between models and abundance measurements of heavy elements in stars, including in binaries, and outline some remaining unexplained features.
      Citation: Universe
      PubDate: 2022-03-29
      DOI: 10.3390/universe8040220
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 221: Does the GRB Duration Depend on Redshift'

    • Authors: Istvan Horvath, Istvan I. Racz, Zsolt Bagoly, Lajos G. Balázs, Sandor Pinter
      First page: 221
      Abstract: Several hundred gamma-ray burst (GRB) redshifts have been determined to date. One of the other important properties—besides the distance—of the GRBs is the duration of the burst. In this paper, we analyse these two important quantities of the phenomena. In this paper, we map the two-dimensional distribution and explore some suspicious areas. As it is well known that the short GRBs are closer than the others, we search for parts in the Universe where the GRB duration is different from the others. We also analyse whether there are any ranges in the duration where the redshifts differ. We find some suspicious areas, however, no other significant region was found than the short GRB region.
      Citation: Universe
      PubDate: 2022-03-30
      DOI: 10.3390/universe8040221
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 222: From Hopf Algebra to Braided

    • Authors: Clay James Grewcoe, Larisa Jonke, Toni Kodžoman, George Manolakos
      First page: 222
      Abstract: We show that an L∞-algebra can be extended to a graded Hopf algebra with a codifferential. Then, we twist this extended L∞-algebra with a Drinfel’d twist, simultaneously twisting its modules. Taking the L∞-algebra as its own (Hopf) module, we obtain the recently proposed braided L∞-algebra. The Hopf algebra morphisms are identified with the strict L∞-morphisms, whereas the braided L∞-morphisms define a more general L∞-action of twisted L∞-algebras.
      Citation: Universe
      PubDate: 2022-04-01
      DOI: 10.3390/universe8040222
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 223: The Poincaré Index and Its

    • Authors: Alexander G. Aleksandrov
      First page: 223
      Abstract: We discuss an approach to the problem of calculating the local topological index of vector fields given on complex spaces or varieties with singularities developed by the author over the past few years. Our method is based on the study of the homology of a contravariant version of the classical Poincaré–de Rham complex. This idea allows not only simplifying the calculations, but also clarifying the meaning of the basic constructions underlying many papers on the subject. In particular, in the graded case, the index can be expressed explicitly in terms of the elementary symmetric polynomials. We also considered some useful applications in physics, mechanics, control theory, the theory of bifurcations, etc.
      Citation: Universe
      PubDate: 2022-04-02
      DOI: 10.3390/universe8040223
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 224: Scattered Radiation of Protoplanetary Disks

    • Authors: Vladimir P. Grinin, Larisa V. Tambovtseva
      First page: 224
      Abstract: Scattered radiation of circumstellar (CS) dust plays an important role in the physics of young stars. Its observational manifestations are various but more often they are connected with the appearance of intrinsic polarization in young stars and their CS disks. In our brief review we consider two classes of astrophysical objects in which the participation of scattered radiation is key for understanding their nature. First of all, these are irregular variables (UX Ori type stars). The modern idea of their nature and the mechanism of their variability has been formed thanks to synchronous observations of their linear polarization and brightness. The second class of objects is the CS disks themselves. Their detailed investigation became possible due to observations in polarized light using a coronographic technique and large telescopes.
      Citation: Universe
      PubDate: 2022-04-02
      DOI: 10.3390/universe8040224
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 225: Introduction to Quantization of Conformal

    • Authors: Lesław Rachwał
      First page: 225
      Abstract: A method for consistent quantization of conformal gravity treating conformal symmetry in a very controllable way is presented. First, we discuss local conformal symmetry in the framework of gravitational interactions, where we view it as an example of a general gauge theory. We also present some early attempts at quantization of conformal gravity and use the generalized framework of covariant quantization due to Faddeev and Popov. Some salient issues such as the need for conformal gauge-fixing, an issue with conformal third ghosts, and discontinuities in conformal gravity are studied as well. Finally, we provide some explanations of the original ad hoc methods of computation valid at the first quantum loop level in conformal gravity.
      Citation: Universe
      PubDate: 2022-04-06
      DOI: 10.3390/universe8040225
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 226: Concurrent Effects between Geomagnetic Storms
           and Magnetospheric Substorms

    • Authors: Tommaso Alberti, Davide Faranda, Giuseppe Consolini, Paola De Michelis, Reik V. Donner, Vincenzo Carbone
      First page: 226
      Abstract: An accurate understanding of dissimilarities in geomagnetic variability between quiet and disturbed periods has the potential to vastly improve space weather diagnosis. In this work, we exploit some recently developed methods of dynamical system theory to provide new insights and conceptual ideas in space weather science. In particular, we study the co-variation and recurrence statistics of two geomagnetic indices, SYM-H and AL, that measure the intensity of the globally symmetric component of the equatorial electrojet and that of the westward auroral electrojet, respectively. We find that the number of active degrees of freedom, required to describe the phase space dynamics of both indices, depends on the geomagnetic activity level. When the magnetospheric substorm activity, as monitored by the AL index, increases, the active number of degrees of freedom increases at high latitudes above the dimension obtained through classical time delay embedding methods. Conversely, a reduced number of degrees of freedom is observed during geomagnetic storms at low latitude by analysing the SYM-H index. By investigating time-dependent relations between both indices we find that a significant amount of information is shared between high and low latitude current systems originating from coupling mechanisms within the magnetosphere–ionosphere system as the result of a complex interplay between processes and phenomena of internal origin activated by the triggering of external source processes. Our observations support the idea that the near-Earth electromagnetic environment is a complex system far from an equilibrium.
      Citation: Universe
      PubDate: 2022-04-06
      DOI: 10.3390/universe8040226
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 227: Muon to Positron Conversion

    • Authors: MyeongJae Lee, Michael MacKenzie
      First page: 227
      Abstract: Lepton-flavor violation (LFV) has been discovered in the neutrino sector by neutrino oscillation experiments. The minimal extension of the Standard Model (SM) to include neutrino masses allows LFV in the charged sector (CLFV) at the loop level, but at rates that are too small to be experimentally observed. Lepton-number violation (LNV) is explicitly forbidden even in the minimally extended SM, so the observation of an LNV process would be unambiguous evidence of physics beyond the SM. The search for the LNV and CLFV process μ−+N(A,Z)→e++N′(A,Z−2) (referred to as μ−→e+) complements 0νββ decay searches, and is sensitive to potential flavor effects in the neutrino mass-generation mechanism. A theoretical motivation for μ−→e+ is presented along with a review of the status of past μ−→e+ experiments and future prospects. Special attention is paid to an uncertain and potentially dominant background for these searches, namely, radiative muon capture (RMC). The RMC high energy photon spectrum is theoretically understudied and existing measurements insufficiently constrain this portion of the spectrum, leading to potentially significant impacts on current and future μ−→e+ work.
      Citation: Universe
      PubDate: 2022-04-07
      DOI: 10.3390/universe8040227
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 228: Superconducting Phases in Neutron Star Cores

    • Authors: Toby S. Wood, Vanessa Graber
      First page: 228
      Abstract: Using a phenomenological Ginzburg–Landau model that includes entrainment, we identify the possible ground states for the neutron and proton condensates in the core of a neutron star, as a function of magnetic field strength. Combining analytical and numerical techniques, we find that much of the outer core is likely to be a “type-1.5” superconductor (instead of a type-II superconductor as often assumed), in which magnetic flux is distributed inhomogeneously, with bundles of magnetic fluxtubes separated by flux-free Meissner regions. We provide an approximate criterion to determine the transition between this type-1.5 phase and the type-I region in the inner core. We also show that bundles of fluxtubes can coexist with non-superconducting regions, but only in a small part of the parameter space.
      Citation: Universe
      PubDate: 2022-04-08
      DOI: 10.3390/universe8040228
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 229: Ultraviolet Finiteness or Asymptotic Safety
           in Higher Derivative Gravitational Theories

    • Authors: Lesław Rachwał
      First page: 229
      Abstract: We present and discuss well known conditions for ultraviolet finiteness and asymptotic safety. The requirements for complete absence of ultraviolet divergences in quantum field theories and existence of a non-trivial fixed point for renormalization group flow in the ultraviolet regime are compared based on the example of a six-derivative quantum gravitational theory in d=4 spacetime dimensions. In this model, it is possible for the first time to have fully UV-finite quantum theory without adding matter or special symmetry, but by inclusion of additional terms cubic in curvatures. We comment on similarities and some apparent differences between the two approaches, but we show that they are both compatible to each other. Finally, we motivate the claim that actually asymptotic safety needs UV-finite models for providing explicit form of the ultraviolet limit of Wilsonian effective actions describing special situations at fixed points.
      Citation: Universe
      PubDate: 2022-04-08
      DOI: 10.3390/universe8040229
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 230: Polyadic Analogs of Direct Product

    • Authors: Steven Duplij
      First page: 230
      Abstract: We propose a generalization of the external direct product concept to polyadic algebraic structures which introduces novel properties in two ways: the arity of the product can differ from that of the constituents, and the elements from different multipliers can be “entangled” such that the product is no longer componentwise. The main property which we want to preserve is associativity, which is gained by using the associativity quiver technique, which was provided previously. For polyadic semigroups and groups we introduce two external products: (1) the iterated direct product, which is componentwise but can have an arity that is different from the multipliers and (2) the hetero product (power), which is noncomponentwise and constructed by analogy with the heteromorphism concept introduced earlier. We show in which cases the product of polyadic groups can itself be a polyadic group. In the same way, the external product of polyadic rings and fields is generalized. The most exotic case is the external product of polyadic fields, which can be a polyadic field (as opposed to the binary fields), in which all multipliers are zeroless fields. Many illustrative concrete examples are presented.
      Citation: Universe
      PubDate: 2022-04-08
      DOI: 10.3390/universe8040230
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 231: Modeling of Magnetospheres of Terrestrial
           Exoplanets in the Habitable Zone around G-Type Stars

    • Authors: Elena S. Belenkaya, Igor I. Alexeev, Marina S. Blokhina
      First page: 231
      Abstract: Using a paraboloid model of an Earth-like exoplanetary magnetospheric magnetic field, developed from a model of the Earth, we investigate the magnetospheric structure of planets located in the habitable zone around G-type stars. Different directions of the stellar wind magnetic field are considered and the corresponding variations in the magnetospheric structure are obtained. It is shown that the exoplanetary environment significantly depends on stellar wind magnetic field orientation and that the parameters of magnetospheric current systems depend on the distance to the stand-off magnetopause point.
      Citation: Universe
      PubDate: 2022-04-08
      DOI: 10.3390/universe8040231
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 232: Bardeen Black Holes in the Regularized 4D
           Einstein–Gauss–Bonnet Gravity

    • Authors: Arun Kumar, Rahul Kumar Walia, Sushant G. Ghosh
      First page: 232
      Abstract: We obtain exact Bardeen black holes to the regularized 4D Einstein–Gauss–Bonnet (EGB) gravity minimally coupled with the nonlinear electrodynamics (NED). In turn, we analyze the horizon structure to determine the effect of GB parameter α on the minimum cutoff values of mass, M0, and magnetic monopole charge, g0, for the existence of a black hole horizon. We obtain an exact expression for thermodynamic quantities, namely, Hawking temperature T+, entropy S+, Helmholtz free energy F+, and specific heat C+ associated with the black hole horizon, and they show significant deviations from the 4D EGB case owing to NED. Interestingly, there exists a critical value of horizon radius, r+c, corresponding to the local maximum of Hawking temperature, at which heat capacity diverges, confirming the second-order phase transition. A discussion on the black holes of alternate regularized 4D EGB gravity belonging to the scalar-tensor theory is appended.
      Citation: Universe
      PubDate: 2022-04-10
      DOI: 10.3390/universe8040232
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 233: Post-AGB Stars as Tracers of AGB
           Nucleosynthesis: An Update

    • Authors: Devika Kamath, Hans Van Winckel
      First page: 233
      Abstract: The chemical evolution of galaxies is governed by the chemical yields from stars, and here we focus on the important contributions from asymptotic giant branch (AGB) stars. AGB nucleosynthesis is, however, still riddled with complexities. Observations from post-asymptotic giant branch (post-AGB) stars serve as exquisite tools to quantify and understand AGB nucleosynthesis. In this contribution, we review the invaluable constraints provided by post-AGB stars with which to study AGB nucleosynthesis, especially the slow neutron capture nucleosynthesis (i.e., the s-process).
      Citation: Universe
      PubDate: 2022-04-11
      DOI: 10.3390/universe8040233
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 234: CP Violation for the Heavens and the Earth

    • Authors: George Wei-Shu Hou
      First page: 234
      Abstract: Electroweak baryogenesis can be driven by the top quark in a general two Higgs doublet model with extra Yukawa couplings. Higgs quartics provide the first order phase transition, while extra top Yukawa coupling ρtt can fuel the cosmic baryon asymmetry through the λtImρtt product, with flavor-changing ρtc coupling as backup. The impressive ACME 2018 bound on the electron electric dipole moment calls for an extra electron coupling ρee for exquisite cancellation among dangerous diagrams, broadening the baryogenesis solution space. The mechanism suggests that extra Yukawa couplings echo the hierarchical structure of standard Yukawa couplings. Phenomenological consequences in the Higgs search and flavor physics are discussed, with μ and τ EDM touched upon.
      Citation: Universe
      PubDate: 2022-04-11
      DOI: 10.3390/universe8040234
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 235: Search for Dark Higgs Inflation with
           Curvature Corrections at LHC Experiments

    • Authors: Lucia Aurelia Popa
      First page: 235
      Abstract: We analyse the dark Higgs inflation model with curvature corrections and explore the possibility to test its predictions by the particle physics experiments at LHC. We show that the dark Higgs inflation model with curvature corrections is strongly favoured by the present cosmological observation. The cosmological predictions of this model, including the quantum corrections of dark Higgs coupling constants and the uncertainty in estimation of the reheating temperature, lead to the dark Higgs mass mφ=0.919± 0.211 GeV and the mixing angle (at 68% CL). We evaluate the FASER and MAPP-1 experiments reach for dark Higgs inflation mass and mixing angle in the 95% CL cosmological confidence region for an integrated luminosity of 3ab−1 at 13 TeV LHC, assuming 100% detection efficiency. We conclude that the dark Higgs inflation model with curvature corrections is a compelling inflation scenario based on particle physics theory favoured by the present cosmological measurements that can leave imprints in the dark Higgs boson searchers at LHC.
      Citation: Universe
      PubDate: 2022-04-12
      DOI: 10.3390/universe8040235
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 236: Significant Variations of Thermospheric
           Nitric Oxide Cooling during the Minor Geomagnetic Storm on 6 May 2015

    • Authors: Zheng Li, Meng Sun, Jingyuan Li, Kedeng Zhang, Hua Zhang, Xiaojun Xu, Xinhua Zhao
      First page: 236
      Abstract: Using observations by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on board the TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics) satellite and simulations by the TIEGCM (Thermosphere-Ionosphere-Electrodynamics General Circulation Model), we investigate the daytime variations of thermospheric nitric oxide (NO) cooling during the geomagnetic storm on 6 May 2015. The geomagnetic storm was minor, as the minimum Dst was −28 nT, the maximum Kp was 5+ and the maximum AE was 1259 nT. However, significant enhancements of peak NO cooling rate and prominent decreases in the peak NO cooling altitude were observed from high latitudes to low latitudes in both hemispheres on the dayside by the SABER instrument. The model simulations underestimate the response of peak NO cooling and have no significant variation of the altitude of peak NO cooling rate on the dayside during this minor geomagnetic storm. By investigating the temporal and latitudinal variations of vertical NO cooling profiles inferred from SABER data, we suggest that the horizontal equatorward winds caused by the minor geomagnetic storm were unexpectedly strong and thus play an important role in inducing these significant daytime NO cooling variations.
      Citation: Universe
      PubDate: 2022-04-12
      DOI: 10.3390/universe8040236
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 237: Lorentzian Vacuum Transitions in
           Hořava–Lifshitz Gravity

    • Authors: Hugo García-Compeán, Daniel Mata-Pacheco
      First page: 237
      Abstract: The vacuum transition probabilities for a Friedmann–Lemaître–Robertson–Walker universe with positive curvature in Hořava–Lifshitz gravity in the presence of a scalar field potential in the Wentzel–Kramers–Brillouin approximation are studied. We use a general procedure to compute such transition probabilities using a Hamiltonian approach to the Wheeler–DeWitt equation presented in a previous work. We consider two situations of scalar fields, one in which the scalar field depends on all the spacetime variables and another in which the scalar field depends only on the time variable. In both cases, analytic expressions for the vacuum transition probabilities are obtained, and the infrared and ultraviolet limits are discussed for comparison with the result obtained by using general relativity. For the case in which the scalar field depends on all spacetime variables, we observe that in the infrared limit it is possible to obtain a similar behavior as in general relativity, however, in the ultraviolet limit the behavior found is completely opposite. Some few comments about possible phenomenological implications of our results are given. One of them is a plausible resolution of the initial singularity. On the other hand, for the case in which the scalar field depends only on the time variable, the behavior coincides with that of general relativity in both limits, although in the intermediate region the probability is slightly altered.
      Citation: Universe
      PubDate: 2022-04-12
      DOI: 10.3390/universe8040237
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 238: Non-Unitary Neutrino Mixing in the
           NOνA Near Detector Data

    • Authors: Ushak Rahaman, Soebur Razzaque
      First page: 238
      Abstract: The νμ→νe oscillation probability over a short baseline (≲1 km) would be negligible for the case when the mixing matrix for three active neutrinos is unitary. However, in the case of a non-unitary mixing of three neutrinos, this probability would be non-negligible due to the so-called “zero distance” effect. Hence, the near detector of accelerator experiments such as NOνA can provide strong constraints on the parameters of the non-unitary mixing with very large statistics. By analyzing the NOνA near-detector data, we find that the non-unitary mixing does not improve fits to the νe or νμ events over the standard unitary mixing. This leads to constraints on the non-unitary parameters: α00>0.911, α10 <0.020, and α11>0.952 at 90% C.L. A combined analysis with the near- and far-detector data does not change these constraints significantly.
      Citation: Universe
      PubDate: 2022-04-13
      DOI: 10.3390/universe8040238
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 239: Editorial to the Special Issue
           “Advances in the Physics of Stars—In Memory of Prof. Yuri N.

    • Authors: Nazar R. Ikhsanov, Galina L. Klimchitskaya, Vladimir M. Mostepanenko
      First page: 239
      Abstract: This Special Issue collects articles devoted to various aspects of astrophysics which can be understood as a science investigating stars, galaxies, their types and properties, stages of their evolution, distribution in the Universe and the interstellar and intergalactic media [...]
      Citation: Universe
      PubDate: 2022-04-13
      DOI: 10.3390/universe8040239
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 240: Observational Constraints and Some Toy Models
           in f(Q) Gravity with Bulk Viscous Fluid

    • Authors: Sanjay Mandal, Abhishek Parida, Pradyumn Kumar Sahoo
      First page: 240
      Abstract: The standard formulation of general relativity fails to describe some recent interests in the universe. It impels us to go beyond the standard formulation of gravity. The f(Q) gravity theory is an interesting modified theory of gravity, where the gravitational interaction is driven by the nonmetricity Q. This study aims to examine the cosmological models with the presence of bulk viscosity effect in the cosmological fluid within the framework of f(Q) gravity. We construct three bulk viscous fluid models, i.e., (i) for the first model, we assuming the Lagrangian f(Q) as linear dependence on Q, (ii) for the second model the Lagrangian f(Q) as a polynomial functional form, and (iii) the Lagrangian f(Q) as a logarithmic dependence on Q. Furthermore, we use 57 points of Hubble data and 1048 Pantheon dataset to constrain the model parameters. Then, we discuss all the energy conditions for each model, which helps us to test the self-consistency of our models. Finally, we present the profiles of the equation of state parameters to test the models’ present status.
      Citation: Universe
      PubDate: 2022-04-13
      DOI: 10.3390/universe8040240
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 241: Directional-Sensitive X-ray/Gamma-ray Imager
           on Board the VZLUSAT-2 CubeSat for Wide Field-of-View Observation of GRBs
           in Low Earth Orbit

    • Authors: Carlos Granja, Rene Hudec, Veronika Maršíková, Adolf Inneman, Ladislav Pína, Daniela Doubravova, Zdenek Matej, Vladimir Daniel, Peter Oberta
      First page: 241
      Abstract: We present a miniaturized and wide field-of-view X-ray and Gamma-ray imager consisting of a segmented 2D optics-collimator coupled to the high-sensitivity semiconductor pixel detector Timepix equipped with a high-Z sensor (CdTe 2000 μm thick). The compact payload has been deployed in low-Earth orbit (LEO) onboard the 3U Cubesat VZLUSAT-2 which was launched on 13 January 2022. The instrument is designed to verify small spacecraft borne observation in open space of hard X-ray and Gamma-ray sources both of celestial and atmospheric origin. High-resolution spectral-sensitive X-ray and Gamma-ray images are provided with enhanced event discrimination and wide field-of-view up to 60°. Description of the instrument together with response evaluation and tests in ground with well-defined sources are presented. The intended observational plan for in-orbit measurements is outlined along with astrophysical goals and issues.
      Citation: Universe
      PubDate: 2022-04-13
      DOI: 10.3390/universe8040241
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 242: Analogue Quantum Gravity in Hyperbolic

    • Authors: Igor I. Smolyaninov, Vera N. Smolyaninova
      First page: 242
      Abstract: It is well known that extraordinary photons in hyperbolic metamaterials may be described as living in an effective Minkowski spacetime, which is defined by the peculiar form of the strongly anisotropic dielectric tensor in these metamaterials. Here, we demonstrate that within the scope of this approximation, the sound waves in hyperbolic metamaterials look similar to gravitational waves, and therefore the quantized sound waves (phonons) look similar to gravitons. Such an analogue model of quantum gravity looks especially interesting near the phase transitions in hyperbolic metamaterials where it becomes possible to switch quantum gravity effects on and off as a function of metamaterial temperature. We also predict strong enhancement of sonoluminescence in ferrofluid-based hyperbolic metamaterials, which looks analogous to particle creation in strong gravitational fields.
      Citation: Universe
      PubDate: 2022-04-14
      DOI: 10.3390/universe8040242
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 243: The Initial-Final Mass Relation of White
           Dwarfs: A Tool to Calibrate the Third Dredge-Up

    • Authors: Paola Marigo
      First page: 243
      Abstract: The initial mass-final mass relationship (IFMR) of white dwarfs (WD) represents a crucial benchmark for stellar evolution models, especially for the efficiency of mixing episodes and mass loss during the asymptotic giant branch (AGB) phase. In this study, we argue that this relation offers the opportunity to constrain the third dredge-up (3DU), with important consequences for chemical yields. The results are discussed in light of recent studies that have identified a kink in the IFMR for initial masses close to 2M⊙. Adopting a physically-sound approach in which the efficiency λ of the 3DU varies as a function of core and envelope masses, we calibrate λ in solar-metallicity TP-AGB models in order to reproduce the final masses of their WD progeny, over the range of initial masses 0.9≤Mi/M⊙≤6. In particular, we find that in low-mass stars with 1.4≲Mi/M⊙≲2.0 the efficiency is small, λ≤0.3, it steeply rises to about λ≃0.65 in intermediate-mass stars with 2.0≤Mi/M⊙≤4.0, and then it drops in massive TP-AGB stars with 4.0≲Mi/M⊙≲6.0. Our study also suggests that a second kink may show up in the IFMR at the transition between the most massive carbon stars and those that are dominated by hot-bottom burning.
      Citation: Universe
      PubDate: 2022-04-14
      DOI: 10.3390/universe8040243
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 244: Nonsingular Black Holes in 4D
           Einstein–Gauss–Bonnet Gravity

    • Authors: Arun Kumar, Dharmanand Baboolal, Sushant G. Ghosh
      First page: 244
      Abstract: Recently, several methods have been proposed to regularize a D→4 limit of Einstein–Gauss–Bonnet (EGB), leading to nontrivial gravitational dynamics in 4D. We present an exact nonsingular black hole solution in the 4D EGB gravity coupled to non-linear electrodynamics and analyze their thermodynamic properties to calculate precise expressions for the black hole mass, temperature, and entropy. Because of the magnetic charge, the thermodynamic quantities are corrected, and the Hawking–Page phase transition is achievable with diverges of the heat capacity at a larger critical radius r=r+C in comparison to the 5D counterpart where the temperature is maximum. Thus, we have a black hole with Cauchy and event horizons, and its evaporation leads to a thermodynamically stable extremal black hole remnant with vanishing temperature, and its size is larger than the 5D counterpart. The entropy does not satisfy the usual exact horizon Bekenstein–Hawking area law of general relativity with a logarithmic area correction term.
      Citation: Universe
      PubDate: 2022-04-14
      DOI: 10.3390/universe8040244
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 245: Maxwell’s Equations in Homogeneous
           Spaces for Admissible Electromagnetic Fields

    • Authors: Valery V. Obukhov
      First page: 245
      Abstract: Maxwell’s vacuum equations are integrated for admissible electromagnetic fields in homogeneous spaces. Admissible electromagnetic fields are those for which the space group generates an algebra of symmetry operators (integrals of motion) that is isomorphic to the algebra of group operators. Two frames associated with the group of motions are used to obtain systems of ordinary differential equations to which Maxwell’s equations reduce. The solutions are obtained in quadratures. The potentials of the admissible electromagnetic fields and the metrics of the spaces contained in the obtained solutions depend on six arbitrary time functions, so it is possible to use them to integrate field equations in the theory of gravity.
      Citation: Universe
      PubDate: 2022-04-15
      DOI: 10.3390/universe8040245
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 246: Multipomeron Model with Collective Effects
           for High-Energy Hadron Collisions

    • Authors: Vladimir Kovalenko, Grigorii Feofilov, Andrei Puchkov, Farkhat Valiev
      First page: 246
      Abstract: We propose the generalized multipomeron exchange model for multiparticle production in high-energy proton–proton, proton–nucleus and heavy-ion collisions. For all of these systems, we consider collectivity effects based on the quark–gluon string fusion concept, where new types of particle-emitting sources—strings with higher tension—are produced. We obtained the model parameters using the data on the multiplicity dependence of the mean transverse momentum of charged particles in pp and pp¯ collisions over a wide energy range (from ISR to LHC). We calculated the yields of strange, multi-strange and charm particles as a function of multiplicity for pp, p-Pb and Pb-Pb collisions at the LHC energy and compared the results with the experimental data.
      Citation: Universe
      PubDate: 2022-04-16
      DOI: 10.3390/universe8040246
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 247: Einstein Field Equation, Recursion Operators,
           Noether and Master Symmetries in Conformable Poisson Manifolds

    • Authors: Mahouton Norbert Hounkonnou, Mahougnon Justin Landalidji, Melanija Mitrović
      First page: 247
      Abstract: We show that a Minkowski phase space endowed with a bracket relatively to a conformable differential realizes a Poisson algebra, confering a bi-Hamiltonian structure to the resulting manifold. We infer that the related Hamiltonian vector field is an infinitesimal Noether symmetry, and compute the corresponding deformed recursion operator. Besides, using the Hamiltonian–Jacobi separability, we construct recursion operators for Hamiltonian vector fields in conformable Poisson–Schwarzschild and Friedmann–Lemaître–Robertson–Walker (FLRW) manifolds, and derive the related constants of motion, Christoffel symbols, components of Riemann and Ricci tensors, Ricci constant and components of Einstein tensor. We highlight the existence of a hierarchy of bi-Hamiltonian structures in both the manifolds, and compute a family of recursion operators and master symmetries generating the constants of motion.
      Citation: Universe
      PubDate: 2022-04-17
      DOI: 10.3390/universe8040247
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 248: GRB 181110A: Constraining the Jet Structure,
           Circumburst Medium and the Initial Lorentz Factor

    • Authors: Song Han, Xinyu Li, Luyao Jiang, Zhiping Jin, Haoning He, Yuanzhu Wang, Daming Wei
      First page: 248
      Abstract: The afterglow data of gamma ray bursts (GRBs) can be used to constrain the physical properties of the fireball (e.g., the jet structure and opening angle) and the circumburst medium. With the peak time of the early afterglow light curve being taken as the deceleration time, one can estimate the initial Lorentz factor of the fireball. In this work, we perform a comprehensive analysis on the prompt emission and the afterglow data of GRB 181110A, where a clear peak is detected by Swift UVOT and XRT in optical to X-ray bands. Prompt emission spectral analysis shows that the spectrum of GRB 181110A is soft, and both hard-to-soft and intensity-tracking spectral evolution are found. By fitting the afterglow light curve and building spectral energy distribution, we find that the standard external forward shock model with a constant circumburst medium is favored, and the jet structure of GRB 181110A tends to be uniform rather than structured. With the peak time of early afterglow emission, we estimate the initial fireball Lorentz factor of GRB 181110A to be Γ0=169−40+92. We also compare GRB 181110A with other typical long GRBs in a statistical context.
      Citation: Universe
      PubDate: 2022-04-18
      DOI: 10.3390/universe8040248
      Issue No: Vol. 8, No. 4 (2022)
  • Universe, Vol. 8, Pages 194: Theory and Phenomenology of a
           Four-Dimensional String–Corrected Black Hole

    • Authors: Kimet Jusufi, Dejan Stojkovic
      First page: 194
      Abstract: We construct an effective four-dimensional string-corrected black hole (4D SCBH) by rescaling the string coupling parameter in a D-dimensional Callan–Myers–Perry black hole. From the theoretical point of view, the most interesting findings are that the string corrections coincide with the so-called generalized uncertainty principle (GUP) corrections to black hole solutions, Bekenstein–Hawking entropy acquires logarithmic corrections, and that there exists a critical value of the coupling parameter for which the black hole temperature vanishes. We also find that, due to the string corrections, the nature of the central singularity may be altered from space-like to time-like singularity. In addition, we study the possibility of testing such a black hole with astrophysical observations. Since the dilaton field does not decouple from the metric, it is not a priori clear that the resulting 4D SCBH offers only small corrections to the Schwarzschild black hole. We used motion of the S2 star around the black hole at the center of our galaxy to constrain the parameters (the string coupling parameter and ADM mass) of the 4D SCBH. To test the weak gravity regime, we calculate the deflection angle in this geometry and apply it to gravitational lensing. To test the strong field regime, we calculate the black hole shadow radius. While we find that the observables change as we change the string coupling parameter, the magnitude of the change is too small to distinguish it from the Schwarzschild black hole. With the current precision, to the leading order terms, the 4D SCBH cannot be distinguished from the Schwarzschild black hole.
      Citation: Universe
      PubDate: 2022-03-21
      DOI: 10.3390/universe8030194
      Issue No: Vol. 8, No. 3 (2022)
  • Universe, Vol. 8, Pages 195: Circular Geodesics in a New Generalization of

    • Authors: Shokoufe Faraji
      First page: 195
      Abstract: This paper introduces an alternative generalization of the static solution with quadrupole moment, the q-metric, that describes a deformed compact object in the presence of an external fields characterized by multipole moments. In addition, we also examine impact of the external fields up to quadrupole on the circular geodesics and the interplay of these two quadrupoles on the place of inner most stable circular orbit (ISCO) in the equatorial plane.
      Citation: Universe
      PubDate: 2022-03-21
      DOI: 10.3390/universe8030195
      Issue No: Vol. 8, No. 3 (2022)
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