arXiv subjects

Payel Sarkar

Publications and source records attributed to Payel Sarkar.

8 recordsLinked to original sources

arXiv2026

Cosmological structure growth in energy-momentum squared gravity

We investigate the cosmological evolution of matter perturbations in the modified gravity model $f(R,T^2)$, where $T^2=T_{\mu\nu}T^{\mu\nu}$ denotes the quadratic contraction of the energy--momentum tensor. Using the gauge-invariant 1+3 covariant formalism, we study the evolution of the matter density contrast and analyze several growth observables, including the growth factor, the growth index, and the weighted growth rate $f\sigma_8$. We consider representative values $n=1/2$ and $n=1/4$, which probe different regimes of the matter--geometry coupling. We show that the growth index decreases with increasing redshift and approaches the standard matter-dominated behavior at early times, while mild scale-dependent deviations from the $\Lambda$CDM model emerge at late times. The model predicts small departures from General Relativity for $n=1/4$, whereas stronger deviations appear for $n=1/2$ and larger values of the coupling parameter $\alpha$. We further compare the theoretical predictions for $f\sigma_8$ with current observational data and find that viable parameter choices remain within the observational $\pm2\sigma$ bounds. These results indicate that $f(R,T^2)$ gravity can provide a viable description of late-time cosmic acceleration and large-scale structure formation while remaining consistent with current growth observations.

astro-ph.CO↗

arXiv2025

Testing the behaviour of exotic matter near wormhole throat in $f(R,T)$ gravity

In this paper, I propose a static wormhole model within modified $f(R,T)$ gravity where $f(R,T)=R+2\lambda T$. The wormhole solutions have been evolved in four cases: three different shape function along with redshift $\phi=\frac{\phi_0}{r}$ and a variable EoS parameter $\omega(r)$ with constant redshift function. I also have explored the energy conditions and the behaviour of exotic matter within the wormhole in all scenarios. Presence of exotic matter violates necessary energy conditions near wormhole throat which gives constraint on modified gravity parameter $\lambda$ in all different cases.

gr-qc↗

arXiv2022

Inflationary Cosmology in a non-minimal $f(R,T)$ gravity theory using a $RT$ mixing term

We investigate a class of inflationary models in modified gravity theories which contain a non-minimal coupling between gravity and a scalar field $\phi$ (inflaton) as $f(R,T)=R \bigl(1+\alpha+ \kappa^4 \beta T \bigr)+\kappa^2\gamma T $ where $\kappa^2=8\pi G$ where $G$ is the Newton's constant. We consider two inflaton potentials of the form (i) $V = V_0 \bigl(1 +\ln{\phi} \bigr)$ and (ii) $V_0\frac{\lambda \phi^p}{1+\lambda\phi^p}$. For a range of potential parameters, we explored the constraints on modified gravity parameters i.e. ($\alpha$, $\beta$ and $\gamma$) in three categories -- (i) $\beta \neq0$, $\alpha=\gamma=0$ (considering $R$ and $RT$ mixing terms), (ii) $\alpha=0$, $\gamma\neq0$, $\beta\neq 0$ ($RT$ mixing term along with $T$ and $R$ terms) and (iii) $\gamma=0$, $\alpha\neq0$, $\beta\neq0$ ($RT$ mixing term along with $R$ term) for the above two potentials. The inclusion of $RT$ mixing term provides the scalar spectral index $n_s$ up to $3\sigma$ limit of PLANCK data, which is $n_s=0.9649\pm0.0042$ as well as the tensor-to-scalar ratio $r<0.106$ and the e-fold parameter $40<N<70$ for both the potentials.

gr-qc↗

arXiv2022

Observational Constraints on the $f(ϕ,T)$ gravity theory

We investigate inflation in modified gravity framework by introducing a direct coupling term between a scalar field $ϕ$ and the trace of the energy momentum tensor $T$ as $f(ϕ,T) = 2 ϕ( κ^{1/2} αT + κ^{5/2} βT^2) $ to the Einstein-Hilbert action. We consider a class of inflaton potentials (i) $V_0 ϕ^p e^{-λϕ}$, (ii) $V_0\frac{ λϕ^p}{1+λϕ^p}$ and investigate the sensitivity of the modified gravity parameters $α$ and $β$ on the inflaton dynamics. We derive the potential slow-roll parameters, scalar spectral index $n_s$, and tensor-to-scalar ratio $r$ in the above $f(ϕ,T)$ gravity theory and analyze the following three choices of modified gravity parameters~(i) Case I:~ $α\neq 0, ~β=0$ i.e. neglecting higher order terms, (ii) Case II:~ $α=0$, $β\neq 0$~ and do the analysis for $T^2$ term, (iii) Case III:~ $α\neq 0$ and $β\neq 0$ i.e. keeping all terms. For a range of potential parameters, we obtain constraints on $α$ and $β$ in each of the above three cases using the WMAP and the PLANCK data.

gr-qc↗

arXiv2022

Inflationary Cosmology in the Modified $f(R, T)$ Gravity

In this work, we study the inflationary cosmology in modified gravity theory $f(R, T) = R + 2 λT$ ($λ$ is the modified gravity parameter) with three distinct class of inflation potentials (i) $ϕ^p e^{-αϕ}$, (ii) $(1-ϕ^p)e^{-αϕ}$ and (iii) $\frac{αϕ^2}{1+αϕ^2}$ where $α$, $p$ are the potential parameters. We have derived the Einstein equation, potential slow-roll parameters, the scalar spectral index $n_s$, tensor to scalar ratio $r$, and tensor spectral index $n_T$ in modified gravity theory. We obtain the range of $λ$ using the spectral index constraints in the parameter space of the potentials. Comparing our results with PLANCK 2018 data and WMAP data, we found out the modified gravity parameter $λ$ lies between $-0.37<λ<1.483$.

gr-qc↗

arXiv2022

Non-Minimal Inflation with a scalar-curvature mixing term $\frac{1}{2} \xi R \phi^2$

We use the PLANCK 2018 and the WMAP data to constraint inflation models driven by a scalar field $\phi$ in the presence of the non-minimal scalar-curvature mixing term $\frac{1}{2}\xi R \phi^2$. We consider four distinct scalar field potentials $\phi^p e^{-\lambda\phi},~(1 - \phi^{p})e^{-\lambda\phi},~(1-\lambda\phi)^p$ and $\frac{\alpha\phi^2}{1+\alpha\phi^2}$ to study inflation in the non-minimal gravity theory. We calculate the potential slow-roll parameters and predict the scalar spectral index $n_s$ and the tensor-to-scalar ratio $r$, in the parameters ($\lambda, p, \alpha$) space of the potentials. We have compared our results with the ones existing in the literature, and this indicates the present status of non-minimal inflation after the release of the PLANCK 2018 data.

astro-ph.CO↗

arXiv2022

Emergent Cosmology in Models of Nonlinear Electrodynamics

Nonlinear electrodynamics, which acts as a source of gravity Einstein field equations, leads to emergent cosmology, an alternative solution which can avoid Big Bang singularity. In this paper, we explore the emerging universe in models of non-linear electrodynamics (described by dimensional parameter $β$) by using the equation of state parameter $ω$ and see how the parameter $β$ helps the universe to cause a transition from a quasi-static Minkowski phase to the inflationary phase of expansion through the point of emergence and subsequently to the phase of normal thermal expansion. We predict the spectral index parameter $n_s = 0.97467$ (scalar spectral index), $r =0.10133$ (tensor to scalar ratio) and $n_T = -0.01267$ (tensor spectral index) of the inflationary perturbation in emergent cosmology of nonlinear electrodynamics corresponding to $β$ = 0.1 and $B_0=10^{-10}$G.

gr-qc↗

arXiv2020

Inflationary cosmology- A new approach using Non-linear electrodynamics

We explore a new kind of field of nonlinear electrodynamics(NLED) which acts as a source of gravity and can accelerate the universe during the inflationary era. We propose a new type of NLED lagrangian which is charecterized by two paremetrs $α$ and $β$. We investigate the classical stability and causality aspects of this model by demanding that the speed ($C_s = \frac{dP}{dρ}$) of the sound wave $C_s^2 > 0$ and $C_s \le 1$ and find that $0 < C_s^2 < 1$ corresponds to $0.25 \le α\le 0.4$ and $0.6 \le βB^2 \le 1$. A study of the deceleration parameter($q = \frac{1}{2}(1 + 3 ω)$, $ω= P/ρ$ being the equation of state parameter) suggests that the value $q < 0$ (i.e. $ω< -1/3$ and $\ddot{a}(t) > 0$ ( the accelerating universe)) requires $βB^2 \ge 0.13$. During inflation, the energy density $ρ_B$ is found to be maximum and is given by $ρ_B^{max} = 0.65/β$ corresponding to $α= 0.3$. The magnetic field necessary to trigger the inflation, is found to be $B (= B_{max}) \simeq \sqrt{\frac{0.4 ρ_B^{max}}{0.65}} = 4 \times 10^{51}~{\rm Gauss}$, where $ρ_{B}^{max}( =10^{64}~{\rm GeV}^4 $) is the energy density of the universe during inflation. The model also predict the e-fold number $N = 71$, which agrees with the experimental result.

hep-ph↗