Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
907
result(s) for
"Jawad, Abdul"
Sort by:
Study of quasinormal modes, greybody factors, and thermodynamics within a regular MOG black hole surrounded by quintessence
In this article, we consider a regular black hole (BH) surrounded by quintessence in the scalar–vector–tensor (S–V–T) version of modified gravity (MOG). We examine the implications of the presence of a quintessence scalar field on astrophysical observable such as quasinormal modes (QNMs), greybody factors (GFs), and thermodynamics. In the vicinity of the MOG BH with quintessence, we calculate the effective potential generated by scalar and electromagnetic field perturbation, and then use the sixth order WKB method to compute the frequencies of the QNMs under these perturbations. We also study the impact of the MOG parameter
α
and the quintessence parameter
c
on QNM frequencies. Our investigation reveals that the combined effects of
α
and
c
parameters lead to significant decrease in oscillation frequencies, while the imaginary part generally rises. We then examine the GFs associated with the BH and found that as the model parameters
α
and
c
increase, GF also increases, and thus less scattering. Additionally, we investigate the thermodynamic quantities and geometries for asymptotically expanded MOG BH. Through heat capacities, Helmholtz and Gibbs free energies, it is observed that this BH shows the stable behavior for various choices of the state parameter of the quintessence
ω
. It is also interesting to mentioned here that Weinhold geometry exhibits the repulsive nature and Ruppiener geometry provides the attractive nature of MOG on the particles for most of the choices of
ω
.
Journal Article
Compatibility of big bang nucleosynthesis in some modified gravities
This paper is devoted to investigate the implications of Einstein-Aether and modified Hořava–Lifshitz theories of gravity to the formation of light elements in the early universe named as big bang nucleosynthesis. We choose different models from these theories for a detailed investigation of big bang nucleosynthesis epoch and compare it with the observational bounds. That is, we compare the deviation of freeze-out temperature Tf with the ΛCDM paradigm and use observational bounds on ΔTfTf to inspect constraints on the involved free parameters of these models. We apply Chi-square test on the Hubble parameter H in each model to analyze the compatibility of model parameters with the observations and find consistent results. We find that chosen models of Einstein-Aether gravity and modified Hořava–Lifshitz gravity can satisfy big bang nucleosynthesis constraints and thus constitute a viable cosmology since they can be source for dark energy sector and late-time accelerated expansion.
Journal Article
Compatibility of gravitational baryogenesis in f(Q, C) gravity
This paper investigates the disparity between matter and antimatter in the universe with the help of gravitational baryogenesis. This phenomenon commenced shortly after the big bang, resulting in a predominance of matter over antimatter. We analyze the mechanism of gravitational baryogenesis (baryon to entropy ratio) under the framework of
f
(
Q
,
C
) gravity, where
Q
indicates non-metricity scalar and
C
denotes the boundary term. This Phenomenon depends on the charge parity violation interaction and for this paper we produce it with the coupling between baryon matter current (
j
ν
) and
∂
ν
(
Q
+
C
)
. In the present work, we evaluate he baryon to entropy ratio (
η
B
S
) by proposing two models of
f
(
Q
,
C
) with the assumption of power-law scale factor for each model and the universe contains perfect fluid throughout. We find that under optimal choice of model parameters, the results of
η
B
S
of propose models in
f
(
Q
,
C
) are compatible with the observational bound. The crux of the current work is that the outcomes of our propose models for generalized case of gravitational baryogenesis are consist with its observational constraint in different eras of the Universe.
Journal Article
Matter growth perturbations and cosmography in modified torsion cosmology
We examine the cosmic evolution of the growth of perturbations with respect to matter content at early and recent past era of the Universe under the framework of non-zero torsion cosmology. Some cosmographic parameters are also discussed. To analyze this cosmic scenario, we formulate the cosmic models with two dark matter considerations and apply spherical collapse formalism. We explore that for model-1 (pressureless matter), the density contrast starts growing in early era of the Universe and with the Universe’s overall expansion, density contrast grows faster for different choices of torsion parameter. In model-2 (matter with non-zero pressure), the density contrast shows enormous growth as compared to overall expansion of the Universe for the perturbed region, which indicates the collapse of the perturbed region and formulation of new large scale matter or galaxy. Further, we analyze the behavior of the growth function for both models with different values of torsion parameter. For model-1, the growth function increases smoothly for different choices of torsion parameter but for the model-2 the behavior of the growth function with nonzero DM and torsion significantly deviates from pressureless DM with zero torsion (
Λ
CDM). We also investigate different cosmographic parameters for both models and analyze their behavior with different choices of torsion parameter and
Λ
CDM. The results show the power-law expansion rate of the accelerating Universe with respect to redshift function.
Journal Article
Cosmic Consequences of Kaniadakis and Generalized Tsallis Holographic Dark Energy Models in the Fractal Universe
We investigate the recently proposed holographic dark energy models with the apparent horizon as the IR cutoff by assuming Kaniadakis and generalized Tsallis entropies in the fractal universe. The implications of these models are discussed for both the interacting (Γ=3Hb2ρm) and noninteracting (b2=0) cases through different cosmological parameters. Accelerated expansion of the universe is justified for both models through deceleration parameter q. In this way, the equation of state parameter ωd describes the phantom and quintessence phases of the universe. However, the coincidence parameter r~=Ωm/Ωd shows the dark energy- and dark matter-dominated eras for different values of parameters. It is also mentioned here that the squared speed of sound gives the stability of the model except for the interacting case of the generalized Tsallis holographic dark energy model. It is mentioned here that the current dark energy models at the apparent horizon give consistent results with recent observations.
Journal Article
Topological charges via Barrow entropy of black hole in metric-affine gravity
This paper examines distinct ensembles such as canonical, mixed, and grand canonical ensembles of recently postulated black hole which is considered to be an ideal solution of metric-affine gravity utilizing the Duan’s
ϕ
-mapping theory. In the scenario, charged and uncharged topological characteristics associated to thermodynamic stability criteria are explored. In contrast to the canonical ensemble, which is always possesses the constant electric and magnetic charges, but mixed ensemble possesses the constant potentials (both magnetic and electric). Also, grand canonical ensemble maintains the constant electric and magnetic potentials for both charges. Initially, we find the topological classes connected via critical points in all of the aforementioned ensembles.
Journal Article
Thermodynamics in Rastall gravity with entropy corrections
We explore the thermodynamic analysis at the apparent horizon in the framework of Rastall theory of gravity. We take different entropies such as the Bakenstein, logarithmic corrected, power law corrected, and the Renyi entropies. We investigate the first law and generalized second law of thermodynamics analytically for these entropies which hold under certain conditions. Furthermore, the behavior of the total entropy in each case is analyzed. As a result, it is implied that the generalized second law of thermodynamics is satisfied. We also check whether the thermodynamic equilibrium condition for these entropies is met at the present horizon.
Journal Article
Tsallis entropy inspires geometric thermodynamics of specific black hole
In this paper, we analyze the thermodynamics of five-dimensional Schwarzschild AdS black hole in AdS5×S5 spacetime in the presence of Tsallis entropy. Since the cosmological constant Λ is considered as thermodynamical pressure with volume as its conjugate, but this explanation cannot be employed in AdS/CFT correspondence. In this study, we associate cosmological constant Λ in boundary gauge theory with the number of colors N and chemical potential is taken to be its thermodynamic conjugate. The two geometric parameters in the AdS black hole, r and L are substituted for two thermodynamic parameters in the micro-canonical ensemble, which are considered to be entropy S and N2. Moreover, we evaluate several thermodynamical geometry formulations, including Weinhold, Ruppeiner, and Quevedo and derive associated scalar curvatures for five-dimensional Schwarzschild AdS black hole. It is suggested that all these geometries show repulsive/attractive forces on the particles at different phases of entropy.
Journal Article
Effects of thermal fluctuations on non-minimal regular magnetic black hole
We analyze the effects of thermal fluctuations on a regular black hole (RBH) of the non-minimal Einstein–Yang–Mill theory with gauge field of magnetic Wu–Yang type and a cosmological constant. We consider the logarithmic corrected entropy in order to analyze the thermal fluctuations corresponding to non-minimal RBH thermodynamics. In this scenario, we develop various important thermodynamical quantities, such as entropy, pressure, specific heats, Gibb’s free energy and Helmholtz free energy. We investigate the first law of thermodynamics in the presence of logarithmic corrected entropy and non-minimal RBH. We also discuss the stability of this RBH using various frameworks such as the
γ
factor (the ratio of heat capacities), phase transition, grand canonical ensemble and canonical ensemble. It is observed that the non-minimal RBH becomes globally and locally more stable if we increase the value of the cosmological constant.
Journal Article