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Universe
Number of Followers: 6 Open Access journal ISSN (Print) 2218-1997 Published by MDPI [84 journals] |
- Universe, Vol. 8, Pages 249: A Mesofractal Model of Interstellar
Cloudiness
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
Conditions
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
Neutrinos
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
Backgrounds
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
Variables
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
Scales
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 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
Observations
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
Telescopes
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
L∞-Algebra
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
Applications
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
Gravity
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.
Gnedin”
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
Metamaterials
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 189: The “ER = EPR” Conjecture and
Generic Gravitational Properties: A Universal Topological Linking Model of
the Correspondence between Tripartite Entanglement and Planck-Scale
Wormholes
Authors: Elias Zafiris, Albrecht von Müller
First page: 189
Abstract: The “ER = EPR” conjecture, conceived by Maldacena and Susskind, is grounded on the notion that a gravitational theory in the bulk is dual to the corresponding quantum field theory on the boundary in accordance to the AdS/CFT correspondence. The conjecture pertains to the idea that Einstein-Rosen (ER) spacetime bridges and Einstein-Podolsky-Rosen (EPR) quantum entanglement may be considered as dually equivalent. Since ER bridges refer to the connectivity between black holes, the “ER = EPR” conjecture implies that black holes connected by ER bridges are entangled, and conversely, that entangled black holes are connected by ER bridges. However, the instance of the maximally entangled tripartite (GHZ) quantum state points to the necessity of devising a model of non-classical Planck scale ER bridges going beyond the standard description of these bridges in spacetime. Based on the topological structure of the maximally entangled GHZ state, we propose that a universal topological link, called the Borromean rings, furnishes a particular linking structure that is able to unravel the equavalence between entanglement and wormholes, and thus, to address the validity of the “ER = EPR” conjecture beyond the initial context of the AdS/CFT correspondence. As a consequence, we propose the explicit construction of distinguishable extensions of the smooth classical spacetime manifold taking place in the transition to the quantum gravity regime according to a naturally induced physical criterion of gravitational generic properties following from this intrinsic topological qualification of the “ER = EPR” conjecture.
Citation: Universe
PubDate: 2022-03-18
DOI: 10.3390/universe8030189
Issue No: Vol. 8, No. 3 (2022)
- Universe, Vol. 8, Pages 190: Can Asteroid Belts Exist in the
Luyten’s System'
Authors: Mattia Galiazzo, Elizabeth A. Silber, Rudolf Dvorak
First page: 190
Abstract: The extra-solar planetary system Luyten is relatively close (12.3 light years) to our Sun. The Luyten’s red dwarf star is orbited by four planets, two of them Earth-like (in mass) and in 4:1 resonance. Extra-solar systems might contain asteroid belts such as ours. Therefore, it is important to investigate whether it is possible to have a stable population of minor bodies and compare them to those in our system. The study of extra-solar systems is crucial for understanding the evolution of planetary systems in general. Here, we investigate the stability of two possible asteroid populations in the Luyten’s system: the main asteroid belt between the two inner and two outer planets, and an outer asteroid belt, situated beyond the planets. We also explore the likelihood of observing an asteroid or a dwarf planet in this system. Our study suggests that the existence of asteroid belts is possible, notably the main belt at 0.09–0.53 au from the star and an outer belt (with the inner boundary at 0.85 au and the outer boundary at ∼66,000 au). The average Yarkovsky drift for the Luyten’s main asteroid belt is ∼0.5×10−4 au/Myr for km-size objects. The Luyten’s system might host extra-solar minor bodies, some of which could be capable of entering our own system. Presently, no asteroids can be detected in the Luyten’s system, not even a Ceres-sized body, because the detection signal using the radial velocity method is at least two orders of magnitude less than that required for discerning such objects. The detection probability of an asteroid in the Luyten belt similar to Ceres is about 1.3%, which is less than the probability of finding Luyten B (∼3%).
Citation: Universe
PubDate: 2022-03-19
DOI: 10.3390/universe8030190
Issue No: Vol. 8, No. 3 (2022)
- Universe, Vol. 8, Pages 191: RR Lyrae Stars and Anomalous Cepheids as
Population Tracers in Local Group Galaxies
Authors: Matteo Monelli, Giuliana Fiorentino
First page: 191
Abstract: We discuss the use and importance of pulsating variable stars as population tracers in Local Group galaxies. Among bright variable crossing the classical instability strip, we mostly focus on RR Lyrae stars and Anomalous Cepheids. We discuss their pulsational properties and how it is possible to use them to constrain the evolution and star formation history of the host galaxy. We discuss RR Lyrae stars as tracers of the old population, and how they can be used to trace the accretion history of large galaxies such as the Milky Way and M31, and also the early chemical evolution. Moreover, we show that the frequency of Anomalous Cepheids follows different relations, and therefore trace the intermediate-age star formation. Finally, we discuss the different methods to derive distances and the impact of the Gaia mission.
Citation: Universe
PubDate: 2022-03-19
DOI: 10.3390/universe8030191
Issue No: Vol. 8, No. 3 (2022)
- Universe, Vol. 8, Pages 192: A Subtle Aspect of Minimal Lengths in the
Generalized Uncertainty Principle
Authors: Michael Bishop, Joey Contreras, Douglas Singleton
First page: 192
Abstract: In this work, we point out an overlooked and subtle feature of the generalized uncertainty principle (GUP) approach to quantizing gravity: namely that different pairs of modified operators with the same modified commutator, [X^,P^]=iħ(1+βp2), may have different physical consequences such as having no minimal length at all. These differences depend on how the position and/or momentum operators are modified rather than only on the resulting modified commutator. This provides guidance when constructing GUP models since it distinguishes those GUPs that have a minimal length scale, as suggested by some broad arguments about quantum gravity, versus GUPs without a minimal length scale.
Citation: Universe
PubDate: 2022-03-20
DOI: 10.3390/universe8030192
Issue No: Vol. 8, No. 3 (2022)
- Universe, Vol. 8, Pages 193: Spin Precession in the Gravity Wave Analogue
Black Hole Spacetime
Authors: Chandrachur Chakraborty, Banibrata Mukhopadhyay
First page: 193
Abstract: It was predicted that the spin precession frequency of a stationary gyroscope shows various anomalies in the strong gravity regime if its orbit shrinks, and eventually, its precession frequency becomes arbitrarily high very close to the horizon of a rotating black hole. Considering the gravity waves of a flowing fluid with a vortex in a shallow basin, which acts as a rotating analogue black hole, one can observe the predicted strong gravity effect on the spin precession in the laboratory. Attaching a thread with the buoyant particles and anchoring it to the bottom of the fluid container with a short-length miniature chain, one can construct a simple local test gyroscope to measure the spin precession frequency in the vicinity of the gravity wave analogue black hole. The thread acts as the axis of the gyroscope. By regulating the orbital frequency of the test gyroscope, one can also measure the strong gravity Lense–Thirring effect and geodetic/de-Sitter effect with this experimental set-up as the special cases. For example, to measure the Lense–Thirring effect, the length of the miniature chain can be set to zero, so that the gyroscope becomes static. One can also measure the geodetic precession with this system by orbiting the test gyroscope in the so-called Keplerian frequency around the non-rotating analogue black hole that can be constructed by making the rotation of the fluid/vortex negligible compared to its radial velocity.
Citation: Universe
PubDate: 2022-03-20
DOI: 10.3390/universe8030193
Issue No: Vol. 8, No. 3 (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
q-Metric
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)