Advances in High Energy Physics
[SJR: 1.334] [H-I: 12] [14 followers] Follow
Open Access journal
ISSN (Print) 1687-7357 - ISSN (Online) 1687-7365
Published by Hindawi Publishing Corporation [402 journals]
- Will There Be Future Deceleration' A Study of Particle Creation
Mechanism in Nonequilibrium Thermodynamics
Abstract: The paper deals with nonequilibrium thermodynamics based on adiabatic particle creation mechanism with the motivation of considering it as an alternative choice to explain the recent observed accelerating phase of the universe. Using Friedmann’s equations, it is shown that the deceleration parameter () can be obtained from the knowledge of the particle production rate (). Motivated by thermodynamical point of view, cosmological solutions are evaluated for the particle creation rates in three cosmic phases, namely, inflation, matter dominated era, and present late time acceleration. The deceleration parameter () is expressed as a function of the redshift parameter (), and its variation is presented graphically. Also, statefinder analysis has been presented graphically in three different phases of the universe. Finally, two noninteracting fluids with different particle creation rates are considered as cosmic substratum, and deceleration parameter () is evaluated. Whether more than one transition of is possible or not is examined by graphical representations.
PubDate: Wed, 08 Apr 2015 06:15:04 +000
- Decays with the QCD Factorization Approach
Abstract: We studied the nonleptonic , decays with the QCD factorization approach. It is found that the Cabibbo favored processes of , , are the promising decay channels with branching ratio larger than 1%, which should be observed earlier by the LHCb collaboration.
PubDate: Sun, 05 Apr 2015 15:58:41 +000
- Global Properties in High Energy Collisions
PubDate: Thu, 26 Mar 2015 06:40:52 +000
- Transverse Momentum Distributions of Hadrons Produced in Pb-Pb Collisions
at LHC Energy TeV
Abstract: The transverse momentum spectra of several types of hadrons, , , , , , , , , , and produced in most central Pb-Pb collisions at LHC energy TeV have been studied at midrapidity () using an earlier proposed unified statistical thermal freeze-out model. The calculated results are found to be in good agreement with the experimental data measured by the ALICE experiment at LHC. The model calculation fits provide the thermal freeze-out conditions in terms of the temperature and collective flow effect parameters for different particle species. Interestingly the model parameter fits to the experimental data reveal stronger collective flow in the system and lesser freeze-out temperatures of the different particle species as compared to Au-Au collisions at RHIC. The strong increase of the collective flow appears to be a consequence of the increasing particle density at LHC. The model used incorporates a longitudinal as well as transverse hydrodynamic flow. The chemical potential has been assumed to be nearly equal to zero for the bulk of the matter owing to high degree of nuclear transparency effect at such collision energies. The contributions from heavier decay resonances are also taken into account.
PubDate: Wed, 25 Mar 2015 12:35:10 +000
- Search for Long-Range Correlations in Relativistic Heavy-Ion Collisions at
Abstract: Long-range correlations are searched for by analysing the experimental data on 16O-AgBr and 32S-AgBr collisions at 200 A GeV/c and the results are compared with the predictions of a multi phase transport (AMPT) model. The findings reveal that the observed forward-backward (F-B) multiplicity correlations are mainly of short range in nature. The range of F-B correlations are observed to extend with increasing projectile mass. The observed extended range of F-B correlations might be due to overall multiplicity fluctuations arising because of nuclear geometry. The findings are not sufficient for making any definite conclusions regarding the presence of long-range correlations.
PubDate: Wed, 25 Mar 2015 12:18:55 +000
- Tsallis Statistical Interpretation of Transverse Momentum Spectra in
High-Energy pA Collisions
Abstract: In Tsallis statistics, we investigate charged pion and proton production for pCu and pPb interactions at 3, 8, and 15 GeV/c. Two versions of Tsallis distribution are implemented in a multisource thermal model. A comparison with experimental data of the HARP-CDP group shows that they both can reproduce the transverse momentum spectra, but the improved form gives a better description. It is also found that the difference between q and q′ is small when the temperature T = T′ for the same incident momentum and angular interval, and the value of q is greater than q′ in most cases.
PubDate: Wed, 25 Mar 2015 11:16:53 +000
- Charged Particle, Photon Multiplicity, and Transverse Energy Production in
High-Energy Heavy-Ion Collisions
Abstract: We review the charged particle and photon multiplicities and transverse energy production in heavy-ion collisions starting from few GeV to TeV energies. The experimental results of pseudorapidity distribution of charged particles and photons at different collision energies and centralities are discussed. We also discuss the hypothesis of limiting fragmentation and expansion dynamics using the Landau hydrodynamics and the underlying physics. Meanwhile, we present the estimation of initial energy density multiplied with formation time as a function of different collision energies and centralities. In the end, the transverse energy per charged particle in connection with the chemical freeze-out criteria is discussed. We invoke various models and phenomenological arguments to interpret and characterize the fireball created in heavy-ion collisions. This review overall provides a scope to understand the heavy-ion collision data and a possible formation of a deconfined phase of partons via the global observables like charged particles, photons, and the transverse energy measurement.
PubDate: Wed, 25 Mar 2015 08:45:54 +000
- On Extraction of Chemical Potentials of Quarks from Particle Transverse
Momentum Spectra in High Energy Collisions
Abstract: We present two methods to extract the chemical potentials of quarks in high energy collisions. The first method is based on the ratios of negatively/positively charged particles, and the temperatures extracted from the transverse momentum spectra of related hadrons are needed. The second method is based on the chemical potentials of some particles, and we also need the transverse momentum spectra of related hadrons. To extract the quark chemical potentials, we would like to propose experimental collaborations to measure simultaneously not only the transverse momentum spectra of , , , , , and , but also those of , , , and (even those of , , and ) in high energy nuclear collisions.
PubDate: Wed, 25 Mar 2015 08:19:30 +000
- Axially Symmetric-dS Solution in Teleparallel Gravity Theories
Abstract: We apply a tetrad field with six unknown functions to Einstein field equations. Exact vacuum solution, which represents axially symmetric-dS spacetime, is derived. We multiply the tetrad field of the derived solution by a local Lorentz transformation which involves a generalization of the angle and get a new tetrad field. Using this tetrad, we get a differential equation from the scalar torsion . Solving this differential equation we obtain a solution to the gravity theories under certain conditions on the form of and its first derivatives. Finally, we calculate the scalars of Riemann Christoffel tensor, Ricci tensor, Ricci scalar, torsion tensor, and its contraction to explain the singularities associated with this solution.
PubDate: Tue, 24 Mar 2015 13:41:00 +000
- Coupled Scalar Fields Oscillons and Breathers in Some Lorentz Violating
Abstract: We discuss the impact of the breaking of the Lorentz symmetry on the usual oscillons, the so-called flat-top oscillons, and the breathers. Our analysis is performed by using a Lorentz violation scenario rigorously derived in the literature. We show that the Lorentz violation is responsible for the origin of a kind of deformation of the configuration, where the field configuration becomes oscillatory in a localized region near its maximum value. Furthermore, we show that the Lorentz breaking symmetry produces a displacement of the oscillon along the spatial direction; the same feature is present in the case of breathers. We also show that the effect of a Lorentz violation in the flat-top oscillon solution is responsible by the shrinking of the flat-top. Furthermore, we find analytically the outgoing radiation; this result indicates that the amplitude of the outgoing radiation is controlled by the Lorentz breaking parameter, in such a way that this oscillon becomes more unstable than its symmetric counterpart; however, it still has a long living nature.
PubDate: Wed, 18 Mar 2015 10:10:57 +000
- Analytical Calculation of Stored Electrostatic Energy per Unit Length for
an Infinite Charged Line and an Infinitely Long Cylinder in the Framework
of Born-Infeld Electrostatics
Abstract: More than 80 years ago, Born-Infeld electrodynamics was proposed in order to remove the point charge singularity in Maxwell electrodynamics. In this work, after a brief introduction to Lagrangian formulation of Abelian Born-Infeld model in the presence of an external source, we obtain the explicit forms of Gauss’s law and the energy density of an electrostatic field for Born-Infeld electrostatics. The electric field and the stored electrostatic energy per unit length for an infinite charged line and an infinitely long cylinder in Born-Infeld electrostatics are calculated. Numerical estimations in this paper show that the nonlinear corrections to Maxwell electrodynamics are considerable only for strong electric fields. We present an action functional for Abelian Born-Infeld model with an auxiliary scalar field in the presence of an external source. This action functional is a generalization of the action functional which was presented by Tseytlin in his studies on low energy dynamics of D-branes (Nucl. Phys. B469, 51 (1996); Int. J. Mod. Phys. A 19, 3427 (2004)). Finally, we derive the symmetric energy-momentum tensor for Abelian Born-Infeld model with an auxiliary scalar field.
PubDate: Tue, 17 Mar 2015 13:43:35 +000
- The Quantum Effects Role on Weibel Instability Growth Rate in Dense Plasma
Abstract: The Weibel instability is one of the basic plasma instabilities that plays an important role in stopping the hot electrons and energy deposition mechanism. In this paper, combined effect of the density gradient and quantum effects on Weibel instability growth rate is investigated. The results have shown that, by increasing the quantum parameter, for large wavelengths, the Weibel instability growth rate shrinks to zero. In the large wavelengths limit, the analysis shows that quantum effects and density gradient tend to stabilize the Weibel instability. The density perturbations have decreased the growth rate of Weibel instability in the near corona fuel, . In the small wavelengths limit, for the density gradient, , the tunneling quantum effects increase anisotropy in the phase space. The quantum tunneling effect leads to an unexpected increase in the Weibel instability growth rate.
PubDate: Sun, 15 Mar 2015 13:02:21 +000
- Retracted: Extracting the QCD Cutoff Parameter Using the Bernstein
Polynomials and the Truncated Moments
PubDate: Thu, 12 Mar 2015 07:23:10 +000
- Cosmological Evolution of Pilgrim Dark Energy in Gravity
Abstract: We analyze the behavior of pilgrim dark energy with Hubble horizon in gravity. We reconstruct the models through correspondence phenomenon by assuming two values of pilgrim dark energy parameter . We evaluate the equation of state parameter which shows evolution of the universe in the quintessence, vacuum, and phantom phase for both cases of and give favor the pilgrim dark energy phenomenon. Also, squared speed of sound exhibits the stability of model for both cases of . The also provides freezing and thawing regions in this scenario. In this framework, the plane also corresponds to different dark energy scenarios.
PubDate: Tue, 10 Mar 2015 14:16:36 +000
- Thermal Properties of Light Tensor Mesons via QCD Sum Rules
Abstract: The thermal properties of (1270), (1320), and (1430) light tensor mesons are investigated in the framework of QCD sum rules at finite temperature. In particular, the masses and decay constants of the light tensor mesons are calculated taking into account the new operators appearing at finite temperature. The numerical results show that, at the point at which the temperature-dependent continuum threshold vanishes, the decay constants decrease with amount of (70–85)% compared to their vacuum values, while the masses diminish about (60–72)% depending on the kinds of the mesons under consideration. The results obtained at zero temperature are in good consistency with the experimental data as well as the existing theoretical predictions.
PubDate: Tue, 10 Mar 2015 13:37:31 +000
- Lepton Number Violation and Neutrino Masses in 3-3-1 Models
Abstract: Lepton number violation and its relation to neutrino masses are investigated in several versions of the model. Spontaneous and explicit violation and conservation of the lepton number are considered. In one of the models (the so-called economical one), the lepton number is spontaneously violated and it is found that the would be Majoron is not present because it is gauged away, providing in this way the longitudinal polarization component to a now massive gauge field.
PubDate: Tue, 10 Mar 2015 06:50:08 +000
- Quintessence and Holographic Dark Energy in Gravity
Abstract: We regard theory as an efficient tool to explain the current cosmic acceleration and associate its evolution with the known dark energy models. The numerical scheme is applied to reconstruct theory from dark energy model with constant equation of state parameter and holographic dark energy model. We set the model parameters and as describing the different evolution eras and show the distinctive behavior of each case realized in theory. We also present the future evolution of reconstructed and find that it is consistent with the recent observations.
PubDate: Mon, 09 Mar 2015 11:21:53 +000
- Neutron Interferometry at the National Institute of Standards and
Abstract: Neutron interferometry has proved to be a very precise technique for measuring the quantum mechanical phase of a neutron caused by a potential energy difference between two spatially separated neutron paths inside interferometer. The path length inside the interferometer can be many centimeters (and many centimeters apart) making it very practical to study a variety of samples, fields, potentials, and other macroscopic medium and quantum effects. The precision of neutron interferometry comes at a cost; neutron interferometers are very susceptible to environmental noise that is typically mitigated with large, active isolated enclosures. With recent advances in quantum information processing especially quantum error correction (QEC) codes we were able to demonstrate a neutron interferometer that is insensitive to vibrational noise. A facility at NIST’s Center for Neutron Research (NCNR) has just been commissioned with higher neutron flux than the NCNR’s older interferometer setup. This new facility is based on QEC neutron interferometer, thus improving the accessibility of neutron interferometry to the greater scientific community and expanding its applications to quantum computing, gravity, and material research.
PubDate: Mon, 09 Mar 2015 07:46:40 +000
- Status of the GRANIT Facility
Abstract: The GRANIT facility is a follow-up project, which is motivated by the recent discovery of gravitational quantum states of ultracold neutrons. The goal of the project is to approach the ultimate accuracy in measuring parameters of such quantum states and also to apply this phenomenon and related experimental techniques to a broad range of applications in particle physics as well as in surface and nanoscience studies. We overview the current status of this facility, the recent test measurements, and the nearest prospects.
PubDate: Mon, 09 Mar 2015 06:14:37 +000
- Effect of Hadron Contamination on Dielectron Signal Reconstruction in
Heavy Flavor Production Measurements
Abstract: Dielectron signal reconstruction is an important tool for heavy flavor measurements because of its trigger feasibility and its relatively straightforward particle identification process. However, in the case of time projection chamber detectors, some hadron contamination is unavoidable, even if additional means are used to improve the particle identification process. In this paper, we investigate the effects of hadron (protons, pions, and kaons) contamination on the dielectron signal reconstruction process in the measurement of and electrons from heavy flavor hadron decays.
PubDate: Sun, 08 Mar 2015 11:31:52 +000
- Production and Decay of Up-Type and Down-Type New Heavy Quarks through
Anomalous Interactions at the LHC
Abstract: We study the process (where and and ) through the anomalous interactions of the new heavy quarks at the LHC. Considering the present limits on the masses and mixings, the signatures of the heavy quark anomalous interactions are discussed and analysed at the LHC for the center of mass energy of 13 TeV. An important sensitivity to anomalous couplings TeV−1, TeV−1, TeV−1 and TeV−1, TeV−1, TeV−1 for the mass of 750 GeV of the new heavy quarks and can be reached for an integrated luminosity of fb−1.
PubDate: Sun, 08 Mar 2015 09:31:45 +000
- Neutron Scattering on Impurity Nanoclusters in Gel Samples
Abstract: Results of recent SANS experiments with impurity-helium gel (IHG) samples in He-II are presented. We estimate the mean size of the impurity nanoparticles that form the frame of the IHG samples and discuss the possibility to use IHG samples for the production of ultracold neutrons (UCNs) in He-II cooled to the temperature of a few mK, as well as the reflection of UCNs at any temperature. Our results indicate that the most promising materials for these purposes might be the heavy water gel samples with the mean sizes of D2O clusters of nm and the heavy alcohol gel samples with the mean sizes of clusters of nm.
PubDate: Sun, 08 Mar 2015 08:47:36 +000
- UCN Source at an External Beam of Thermal Neutrons
Abstract: We propose a new method for production of ultracold neutrons (UCNs) in superfluid helium. The principal idea consists in installing a helium UCN source into an external beam of thermal or cold neutrons and in surrounding this source with a solid methane moderator/reflector cooled down to ~4 K. The moderator plays the role of an external source of cold neutrons needed to produce UCNs. The flux of accumulated neutrons could exceed the flux of incident neutrons due to their numerous reflections from methane; also the source size could be significantly larger than the incident beam diameter. We provide preliminary calculations of cooling of neutrons. These calculations show that such a source being installed at an intense source of thermal or cold neutrons like the ILL or PIK reactor or the ESS spallation source could provide the UCN density 105 cm−3, the production rate 107 UCN/s−1. Main advantages of such an UCN source include its low radiative and thermal load, relatively low cost, and convenient accessibility for any maintenance. We have carried out an experiment on cooling of thermal neutrons in a methane cavity. The data confirm the results of our calculations of the spectrum and flux of neutrons in the methane cavity.
PubDate: Sun, 08 Mar 2015 08:40:11 +000
- Prospects for Studies of the Free Fall and Gravitational Quantum States of
Abstract: Different experiments are ongoing to measure the effect of gravity on cold neutral antimatter atoms such as positronium, muonium, and antihydrogen. Among those, the project GBAR at CERN aims to measure precisely the gravitational fall of ultracold antihydrogen atoms. In the ultracold regime, the interaction of antihydrogen atoms with a surface is governed by the phenomenon of quantum reflection which results in bouncing of antihydrogen atoms on matter surfaces. This allows the application of a filtering scheme to increase the precision of the free fall measurement. In the ultimate limit of smallest vertical velocities, antihydrogen atoms are settled in gravitational quantum states in close analogy to ultracold neutrons (UCNs). Positronium is another neutral system involving antimatter for which free fall under gravity is currently being investigated at UCL. Building on the experimental techniques under development for the free fall measurement, gravitational quantum states could also be observed in positronium. In this contribution, we report on the status of the ongoing experiments and discuss the prospects of observing gravitational quantum states of antimatter and their implications.
PubDate: Sun, 08 Mar 2015 08:16:45 +000
- Can We Observe the Gravitational Quantum States of Positronium'
Abstract: We consider the feasibility of observing the gravitational quantum states of positronium. The proposed scheme employs the flow-throw technique used for the first observation of this effect with neutrons. Collimation and Stark deceleration of Rydberg positronium atoms allow selecting the required velocity class. If this experiment could be realized with positronium, it would lead to a determination of for this matter-antimatter system at the few % level. As discussed in this contribution, most of the required techniques are currently available but important milestones have to be demonstrated experimentally before such an experiment could become reality. Those are the efficient focusing of a bunched positron beam, Stark deceleration of Rydberg positronium, and its subsequent excitation into states with large angular momentum. We provide an estimate of the efficiencies we expect for these steps and assuming those could be confirmed we calculate the signal rate.
PubDate: Sun, 08 Mar 2015 07:48:42 +000
- Phase Transition of the Higher Dimensional Charged Gauss-Bonnet Black Hole
in de Sitter Spacetime
Abstract: We study the phase transition of charged Gauss-Bonnet-de Sitter (GB-dS) black hole. For black holes in de Sitter spacetime, there is not only black hole horizon, but also cosmological horizon. The thermodynamic quantities on both horizons satisfy the first law of the black hole thermodynamics, respectively; moreover, there are additional connections between them. Using the effective temperature approach, we obtained the effective thermodynamic quantities of charged GB-dS black hole. According to Ehrenfest classification, we calculate some response functions and plot their figures, from which one can see that the spacetime undergoes a second-order phase transition at the critical point. It is shown that the critical values of effective temperature and pressure decrease with the increase of the value of GB parameter .
PubDate: Sun, 01 Mar 2015 12:23:51 +000
- Weak Minimal Area in Entanglement Entropy
Abstract: We revisit the minimal area condition of Ryu-Takayanagi in the holographic calculation of the entanglement entropy, in particular, the Legendre test and the Jacobi test. The necessary condition for the weak minimality is checked via Legendre test and its sufficient nature via Jacobi test. We show for AdS black hole with a strip type entangling region that it is this minimality condition that makes the hypersurface unable to cross the horizon, which is in agreement with that studied earlier by Engelhardt et al. and Hubeny using a different approach. Moreover, demanding the weak minimality condition on the entanglement entropy functional with the higher derivative term puts a constraint on the Gauss-Bonnet coupling; that is, there should be an upper bound on the value of the coupling, .
PubDate: Thu, 26 Feb 2015 11:22:35 +000
- Theoretical and Phenomenological Status of Neutrino Physics: A Brief
Abstract: We present an overview of recent progress in the theoretical and phenomenological studies of neutrino masses, lepton avor mixing, and CP violation. Firstly, We discuss the status of neutrino mass with in the Standard Model (SM) of particle physics. Then the possible ways in which neutrino mass terms can be included in the SM are discussed. The inclusion of new physics beyond the SM inevitably brings new parameters which are not constrained by the present experimental data on neutrino masses and mixing angles and, thus, are free parameters of the theory. We, also, discuss various theoretically motivated phenomenological approaches which can be used to reduce the number of free parameters and, thus, provide an excellent tool to understand the underlying physics of neutrino masses and mixings. Current experimental constraints on the neutrino mass spectrum and the lepton avor mixing parameters, including the recent observation of nonzero , have been summarized. Finally, We discuss the renewed interest in the possible existence of one or more sterile neutrinos and their phenomenology.
PubDate: Wed, 25 Feb 2015 07:36:04 +000
- An Alternative Approach to Solutions of the MGECSC Potential in Presence
of External Electric Field
Abstract: For the first time the Schrödinger equation with more general exponential cosine screened Coulomb potential in the presence of external electric field is solved approximately and analytically by applying an ansatz to eigenfunction of corresponding Hamiltonian and then energy values and wave functions are obtained. Since this potential turns into four different potential cases when considering different cases of the parameters in the potential, energies and eigenfunctions for these four different potentials are already to be found by solving Schrödinger equation with MGECSC potential. Energy values and wave functions obtained by using different values of potential parameters for each of these four different potential are compared with the results of other studies. Since the obtained general solutions in this study have been found in the presence of external electric field, the external electric field effects on systems with the mentioned four different potentials are also easily investigated. One of advantages of the present results and method is that if external electric field is equal to zero, general mathematical structure of corresponding equations does not change and then electric field effect can be eliminated. The presence or absence of electric field does not prevent solving the Schrödinger equation analytically.
PubDate: Mon, 23 Feb 2015 07:26:54 +000
- Holographic Fermions in Anisotropic Einstein-Maxwell-Dilaton-Axion Theory
Abstract: We investigate the properties of the holographic Fermionic system dual to an anisotropic charged black brane bulk in Einstein-Maxwell-Dilaton-Axion gravity theory. We consider the minimal coupling between the Dirac field and the gauge field in the bulk gravity theory and mainly explore the dispersion relation exponents of the Green functions of the dual Fermionic operators in the dual field theory. We find that along both the anisotropic and the isotropic directions the Fermi momentum will be effected by the anisotropy of the bulk theory. However, the anisotropy has influence on the dispersion relation which is almost linear for massless Fermions with charge . The universal properties that the mass and the charge of the Fermi possibly correspond to nonlinear dispersion relation are also investigated.
PubDate: Sun, 22 Feb 2015 12:03:27 +000