arXiv subjects

Snehasish Bhattacharjee

Publications and source records attributed to Snehasish Bhattacharjee.

28 records · Page 2Linked to original sources

arXiv2020

Interacting Tsallis and Rényi Holographic Dark Energy with Hybrid Expansion Law

The manuscript presents the dynamics of Tsallis holographic dark energy (THDE) and Rényi holographic dark energy (RHDE) prescribed by a non-linear interaction in the FRW spacetime and for a scale factor evolving with a composite power law-exponential (hybrid) form. To construct the energy densities of these holographic dark energy models, I assume the Hubble cutoff to be the IR limit. I find that the deceleration parameter undergoes a signature flipping at a redshift $z$ consistent with observations. The EoS parameter $ω_{de}$ for both the HDE models exhibit quite contrasting dynamical behavior despite assuming values close to $-1$ at $z=0$ and therefore consistent with current observations. Next, I find the squared sound speed $c_{s}^{2}$ to be positive for the THDE model ensuring stability against perturbations, whereas for the RHDE model, $c_{s}^{2}<0$ implying instability against perturbations. Furthermore, I analyzed the evolutionary behavior of the EoS parameter of the HDE models by constructing the $ω_{de}-ω_{de}^{'}$ plane and find that the plane lies in the freezing region for the THDE model and in the thawing region for the RHDE model.

gr-qc↗

arXiv2020

Constraining f(R,T) Gravity From The Dark Energy Density Parameter $Ω_Λ$

$f(R,T)$ gravity is a widely used extended theory of gravity introduced in \cite{9} which is a straightforward generalization of $f(R)$ gravity. The action in this extended theory of gravity incorporates well motivated functional forms of the Ricci scalar $R$ and trace of energy momentum tensor $T$. The present manuscript aims at constraining the most widely used $f(R,T)$ gravity model of the form $f(R+2λT)$ to understand its coherency and applicability in cosmology. We communicate here a novel method to find an lower bound on the model parameter $λ\gtrsim -1.9 \times 10^{-8}$ through the equation relating the cosmological constant ($Λ$) and the critical density of the universe ($ρ_{cr}$).

gr-qc↗

arXiv2020

Gravitational baryogenesis in extended teleparallel theories of gravity

The article communicates gravitational baryogenesis in non-minimal $f(T)$ gravity and $f(T,B)$ teleparallel gravity where $T$ denote the torsion scalar and $B$ a boundary term. These extended teleparallel theories of gravity differ from the usual $f(T)$ gravity and therefore could provide key insights in expounding the baryon asymmetry of the universe. Furthermore, such a study also put constraints on the model parameters of these extended teleparallel theory of gravity. I present different baryogenesis interactions proportional to $\partial_{i}T$, $\partial_{i}f(T)$, $\partial_{i}(T+B)$ and $\partial_{i}f(T+B)$ and find that both of these teleparallel theories of gravity yield viable estimates of the baron-to-entropy ratio compatible with observations except for the baryogenesis interaction proportional to $\partial_{i}(T+B)$. It is therefore encouraging to exercise these extended theories of gravity in other cosmological areas to under their efficiency and applicability in characterizing the current state of the universe.

gr-qc↗

arXiv2020

Redshift Drift in $f(R,T)$ Gravity

Redshift drift refers to the phenomena that redshift of cosmic objects is a function of time. Measurement of redshift drift is of fundamental importance in physical cosmology and can be utilized to distinguish different cosmological models. Redshift drift can be expressed in two distinct methods. The first method is related to cosmography, where the Redshift drift is given as a series expansion of cosmological parameters, while the second method is written as a function of Hubble parameter and its time derivatives which ultimately involve field equations of a chosen theory of gravity. By equating corresponding terms from both the series, the model parameter(s) of any modified theory of gravity can be constrained. The present note aims at constraining the model parameter $ζ$ of $f(R,T)$ gravity theory where $f(R,T)= R + ζT$. By equating linear terms in redshift $z$ from both the series, we constrain $ζ$ in the range $-0.51 κ^{2} \lesssim ζ\lesssim -0.47 κ^{2}$, where $κ^{2}=\frac{8 πG}{c^{4}}$.

gr-qc↗

arXiv2020

Accelerating Universe in Hybrid and Logarithmic Teleparallel Gravity

Teleparallel gravity is a modified theory of gravity for which the Ricci scalar $R$ of the underlying geometry in the action is replaced by an arbitrary functional form of torsion scalar $T$. In doing so, cosmology in $% f(T)$ gravity becomes greatly simplified owing to the fact that $T$ contains only the first derivatives of the vierbeins. The article exploits this appealing nature of $f(T)$ gravity and present cosmological scenarios from hybrid and logarithmic teleparallel gravity models of the form $% f=e^{mT}T^n $ and $f=D\log(bT)$ respectively, where $m$, $n$, $D$ and $b$ are free parameters constrained to suffice the late time acceleration. We employ a well motivated parametrization of the deceleration parameter having just one degree of freedom constrained with a $χ^{2}$ test from 57 data points of Hubble data set in the redshift range $0.07<z<2.36$, to obtain the expressions of pressure, density and EoS parameter for both the teleparallel gravity models and study their temporal evolution. We find the deceleration parameter to experience a signature flipping for the $χ^{2}$ value of the free parameter at $z_{tr}\simeq0.6$ which is consistent with latest Planck measurements. Next, we present few geometric diagnostics of this parametrization to understand the nature of dark energy and its deviation from the $Λ$CDM cosmology. Finally, we study the energy conditions to check the consistency of the parameter spaces for both the teleparallel gravity models. We find the SEC to violate for both the models which is an essential recipe to obtain an accelerating universe.

physics.gen-ph↗

arXiv2020

Big Bang Nucleosynthesis and Entropy Evolution in $f(R,T)$ Gravity

The present article is devoted to constrain the model parameter $χ$ for the $f(R,T)= R + χT$ gravity model by employing the constraints coming from big bang nucleosynthesis. We solve the field equations and constrain $χ$ in the range $-0.14 κ^{2} \leq χ\leq 0.84 κ^{2}$ (where $κ^{2} = \frac{8 πG}{c^{4}}$) from the primordial abundances of light elements such as helium-4, deuterium and lithium-7. We found the abundances of helium-4 and deuterium agrees with theoretical predictions, however the lithium problem persists for the $f(R,T)$ gravity model. We also investigate the evolution of entropy for the constrained parameter space of $χ$ for the radiation and dust universe. We report that entropy is constant when $χ= 0$ for the radiation dominated universe, whereas for the dust universe, entropy increases with time. We finally use the constraints to show that $χ$ has negligible influence on the cold dark matter annihilation cross section.

physics.gen-ph↗

arXiv2020

Comprehensive Analysis of a Non-Singular Bounce in $f(R,T)$ Gravitation

The present paper is devoted to the study of bouncing cosmology in $f(R,T)$ modified gravity where we presume $f(R,T) = R + 2 λT$, with $R$ the Ricci scalar, $T$ the trace of energy momentum tensor and $λ$ the model parameter. We present here a novel parametrization of Hubble parameter which is apt in representing a successful bouncing scenario undergoing no singularity. We proceed to present a complete analysis of the proposed bouncing model by studying the evolution of primordial curvature perturbations, energy conditions and stability against linear homogeneous perturbations in flat space-time. We also delineate bouncing cosmology for the proposed model by employing Quintom matter. The present article further communicate for the first time that violation of energy-momentum materialize for both the contracting and expanding universes except for the bouncing epoch with energy flow directed away and into the matter fields for the contracting and expanding universe respectively. We further present a thorough investigation about the feasibility of the proposed bouncing scenario against first and generalized second law of thermodynamics. We found that the proposed bouncing scenario obeys the laws of thermodynamics for the constrained parameter space of $λ$. The manuscript conclude after investigating the viability of the proposed bouncing model in non minimal $f(R,T)$ gravity where $f(R,T) = R + χR T$.

gr-qc↗

arXiv2020

Baryogenesis in $f(Q,\mathcal{T})$ Gravity

The article communicates exploration of gravitational baryogenesis in presence of $f(Q,\mathcal{ T})$ gravity where $Q$ denote the nonmetricity and $\mathcal{ T}$ the trace of the energy momentum tensor. We study various baryogenesis interactions proportional to $\dot{Q}$ and $\dot{Q}f_{Q}$ for the $f(Q,\mathcal{ T})$ gravity model $f(Q,\mathcal{ T})=αQ ^{n+1} + β\mathcal{ T}$, where $α$, $β$ and $n$ are model parameters. Additionally we report the viable parameter spaces for which an observationally consistent baryon-to-entropy can be generated. Our results indicate that $f(Q,\mathcal{ T})$ gravity can contribute significantly and consistently to the phenomenon of gravitational baryognesis.

physics.gen-ph↗

arXiv2020

Gravitational Baryogenesis in Non-Minimal Coupled $f(R,T)$ Gravity

Baryogenesis refers to the theoretical process that occurred in the early history of the universe producing excess of matter over antimatter. Hitherto, fundamental physics which can give rise to such events is unknown. Many theories have emerged which may be able to suffice this conundrum, although concrete understanding is obscure. Gravitational baryogenesis is one such theory introduced by H. Davoudiasl, et al., Phys. Rev. Lett. \textbf{93} (2004) 201301. In this theory, for a CP violating interaction proportional to $\partial_μR$, where R denote Ricci scalar, gravitational baryogenesis is inevitable. In this paper, we have investigated the consequences of CP violating interactions proportional to $\partial_μR$, $\partial_μT$ and $\partial_μf(R,T)$ in the framework of non-minimal f(R,T) gravity. We found that for interactions proportional to $\partial_μR$ and $\partial_μf(R,T)$, baryogenesis can be realized with suitable parameter spaces producing a net baryon asymmetry factor consistent with observations, whereas for interaction proportional to $\partial_μT$, results in a baryon asymmetry incompatible with observations.rther, we obtained baryon to entropy ratio in each case and put constraints on parameters spaces of our model.

physics.gen-ph↗

arXiv2020

Effects of magnetic field on the radiation pressure dominated discs around neutron stars

We supplement the analytic solution obtained by Matthews O. M., et. al., 2005, MNRAS, \textbf{356}, 66 to investigate the steady-state structure of radiation pressure dominated disc under the influence of a stellar magnetic field which deploys a torque. The solutions converge to the non-magnetic Shakura N. I., Sunyaev R. A., 1973, A\& A, \textbf{24}, 337 form when magnetic field of the star tends to zero and also at large radii. Effects of varying the mass accretion rates and the spin period of a typical neutron star on the disc parameters are presented. We further report that the presence of a magnetic correction term $k$ reduces the radial extent upto which radiation pressure and electron scattering continue to be the major source of pressure and opacity respectively. We also report that magnetic effects amplify the viscous timescale several times in the inner disc.

gr-qc↗