arXiv subjects

S. K. Tripathy

Publications and source records attributed to S. K. Tripathy.

At least 37 records · Page 2Linked to original sources

arXiv2022

Dynamical system analysis for accelerating models in non-metricity $f(Q)$ gravity

Two accelerating cosmological models are presented in symmetric teleparallel $f(Q)$ gravity, $Q$ be the non-metricity. The models are constructed based on the assumptions of two different functional forms of $f(Q)$ and a dynamically changing nature of the deceleration parameter that shows transition at $t=2n\pm\sqrt{\frac{4n^2+1}{3}}$, $n$ being a positive constant. In both the models, the equation of state parameter for the dark energy in $f(Q)$ gravity becomes a dynamical quantity and crosses the phantom divide line. The violation of the strong energy condition and the null energy condition at late times are also established. In addition, the dynamical system analysis has been performed and three critical points in each model are identified. In each model, at least one stable node has been observed. To strengthen further, the stability analysis using homogeneous linear perturbations has been performed to ensure the stability of the models.

gr-qc↗

arXiv2022

Role of Extended Gravity Theory in Matter Bounce Dynamics

In this work, we have studied some bouncing cosmologies in the frame work of $f(R,T)$ gravity. The bouncing scenario has been formulated to avoid the big bang singularity. The physical and geometrical parameters are investigated. The effect of the extended gravity theory on the dynamical parameters of the model is investigated. It is found that, the $f(R,T)$ gravity parameter affects the cosmic dynamics substantially. We have also, tested the model through the calculation of the cosmographic coefficients and the $Om(z)$ parameter. A scalar field reconstruction of the bouncing scenario is also carried out. The stability of the model are tested under linear, homogeneous and isotropic perturbations.

gr-qc↗

arXiv2021

Effect of bulk viscosity in cosmic acceleration

In this paper, we have investigated the late time cosmic acceleration issue in the context of $f(R,T)$ gravity. The matter field is considered to be that of viscous fluid. The model has been framed as a mathematical formalism and the effect of viscous fluid on the cosmic expansion has been shown. The equation of state parameter indicates the quintessence behaviour of the Universe at late time. The theoretical results obtained here shows its alignment with the cosmological observations result.

gr-qc↗

arXiv2021

Traversable wormhole models in $f(R)$ gravity

In this work, we analyze the wormhole solutions in $f(R)$ gravity. Specifically we sought for wormhole geometry solutions for the following three shape functions: (i) $b(r)=r_{0}+ρ_{0}r_{0}^{3}\ln\left(\frac{r_{0}}{r}\right)$, (ii) $b(r)=r_{0}+γr_{0}\left(1-\dfrac{r_{0}}{r}\right)$, and (iii) $b(r)=α+βr$, under some legitimate physical conditions on the parameters as well as constants involved here with in the shape functions. It is observed from the graphical plots that the behaviour of the physical parameters are interesting and viable.

gr-qc↗

arXiv2021

Cosmological model with time varying deceleration parameter in $F(R,G)$ gravity

In this paper, we study the dynamical behaviour of the Universe in the $F(R,G)$ theory of gravity, where $R$ and $G$ respectively denote the Ricci scalar and Gauss-Bonnet invariant. Our wide analysis encompasses the energy conditions, cosmographic parameters, $Om(z)$ diagnostic, stability and the viability of reconstructing the referred model through a scalar field formalism. The model obtained here shows the quintessence like behaviour at late times.

gr-qc↗

arXiv2021

Rip cosmological models in extended symmetric teleparallel gravity

In this paper we have investigated some rip cosmological models in an extended symmetric teleparallel gravity theory. We consider the form $f(Q,T)=aQ^m+bT$ in the Einstein-Hilbert action and expressed the field equations and the dynamical parameters in terms of the non-metricity $Q$. Three rip models such as Little Rip, Big Rip and Pseudo Rip are presented. The energy conditions and the cosmographic parameters are derived and analysed for all these models.

gr-qc↗

arXiv2021

Bouncing cosmology in extended gravity and its reconstruction as dark energy model

In this paper, we have presented a bouncing cosmological model of the Universe in an extended theory of gravity. The dynamical behaviour of the model obtained from the flat FLRW space-time along with the violation of null energy condition have been shown. The geometrical parameters show singularity behaviour at the bouncing epoch. The parameters involved in the scale factor play a major role in the bouncing behaviour. In addition, the coupling parameter that resulted in the minimal matter-geometry coupling in the extended gravity has significant role to avoid the singularity of equation of state parameter at the bouncing epoch. Using a linear homogeneous perturbation calculation, we show the stability of the model.

gr-qc↗

arXiv2021

Medium modification type phenomena observed in high-multiplicity p+p collisions at LHC energies

Nuclear modification factor predicts whether a medium is formed in a collision system or not. One may verify, if scaling of momentum (transverse) distribution from heavy-ion systems with incoherent superposition of number of binary collision, is making up the magnitude of elementary like systems. It was observed in a wide range of experimental data that in lower momentum (transverse) region, initial state effects (viz. cold-nuclear matter effect or radial flow) enhances it. While in higher momentum (transverse) region, final state effects (viz. jet quenching or re-scattering effects) suppresses it. In this article we made an attempt to predict and explain if this heavy-ion like effect can be seen in elementary collisions at favorable experimental conditions. We have employed PYTHIA8 model in this regard, and used effects which give collective-like behaviour within the model constraint. Results from this model qualitatively explains the behaviour observed in heavy-ion systems.

hep-ph↗

arXiv2021

Matter Bounce Scenario and the Dynamical aspects in f(Q,T) Gravity

In the context of the late time cosmic acceleration phenomenon, many geometrically modified theories of gravity have been proposed in recent times. In this paper, we have investigated the role of a recently proposed extension of symmetric teleparallel gravity dubbed as f(Q,T) gravity in getting viable cosmological models, where Q and T respectively denote the non-metricity and the trace of energy momentum tensor. We stress upon the mathematical simplification of the formalism in the f(Q,T) gravity and derived the dynamical parameters in more general form in terms of the Hubble parameter. We considered two different cosmological models mimicking non-singular matter bounce scenario. Since energy conditions play a vital role in providing bouncing scenario, we have analyzed different possible energy conditions to show that strong energy condition and null energy condition be violated in this theory. The models considered in the work are validated through certain cosmographic tests and stability analysis.

gr-qc↗

arXiv2021

Model parameters in the context of late time cosmic acceleration in $f(Q,T)$ gravity

The dynamical aspects of some accelerating models are investigated in the framework of an extension of symmetric teleparllel gravity dubbed as f(Q,T) gravity. In this gravity theory, the usual Ricci tensor in the geometrical action is replaced by a functional f(Q,T) where Q is the non-metricity and T is the trace of the energy-momentum tensor. Two different functional forms are considered in the present work. In order to model the Universe, we have considered a signature flipping deceleration parameter simulated by a hybrid scale factor (HSF). The dynamical parameters of the model are derived and analysed. We discuss the role of the parameter space in getting viable cosmological models. It is found that, the models may be useful as suitable geometrical alternatives to the usual dark energy approach.

gr-qc↗

arXiv2021

Cosmological models with Big rip and Pseudo rip Scenarios in extended theory of gravity

In this paper, we have presented the big rip and pseudo rip cosmological models in an extended theory of gravity. The matter field is considered to be that of perfect fluid. The geometrical parameters are adjusted in such a manner that it matches the prescriptions given by cosmological observations, to be specific to the range of Hubble tension $(H_{0})$. The models favor phantom behavior. The violation of strong energy conditions are shown in both the models, as it has become essential in an extended gravity. The representative values of the coupling parameter are significant on the evolution of the universe.

gr-qc↗

arXiv2021

Cosmological models with a Hybrid Scale Factor

In this brief review, we present some cosmological models with a Hybrid Scale Factor (HSF) in the framework of general relativity (GR). The hybrid scale factor fosters an early deceleration as well as a late time acceleration and mimics the present Universe. The dynamical aspects of different cosmological models with HSF in the presence of different matter fields have been discussed.

gr-qc↗

arXiv2021

Dynamics of quasi de Sitter and linear combination of exponential models in extended gravity

In this paper, we have studied the dynamical aspects of some cosmological models in an isotropic space-time within the framework of an extended gravity theory. Two accelerating cosmological models are presented with quasi-de Sitter (QDS) and linear combination of exponential (LCE) scale factors. The geometrical testing mechanism has been performed and analysed. While the results of the QDS model show a departure from the concordant $Λ$CDM model, the resulting behavior of the LCE model seems to be compatible with the $Λ$CDM model only at the present epoch and is incompatible in the near past.

gr-qc↗

arXiv2021

Gravitational baryogenesis models comparison in f(R) Gravity

We have studied the gravitational baryogenesis in f(R) theory of gravity with an anisotropic Bianchi I space-time. The matter field is considered to be that of perfect fluid. Two models pertaining to specific form of Ricci scalar have been presented. The baryon-to-entropy ratio has been derived with the some specific form of Ricci scalar in the anisotropic background. The gravitational baryogenesis is examined and its behaviors are studied.

gr-qc↗

arXiv2021

Modeling of accelerating Universe with bulk viscous fluid in Bianchi V space-time

In this paper, we have investigated a bulk viscous anisotropic Universe and constrained its model parameters with recent $H(z)$ and Pantheon compilation data. Using cosmic chronometric technique, we estimate the present value of Hubble's constant as $H_{0} = 69.39 \pm 1.54~km~s^{-1}Mpc^{-1}$, $70.016 \pm 1.65~km~s^{-1}Mpc^{-1}$ and $69.36 \pm 1.42~km~s^{-1}Mpc^{-1}$ by bounding our derived model with recent $H(z)$ data, Pantheon and joint $H(z)$ and Pantheon data respectively. The present age of the Universe is specified as $t_0= 0.9796H_0^{-1}\sim 13.79$ Gyrs. The model favours a transitioning Universe with the transition red-shift as $z_{t} = 0.73$. We have reconstructed the jerk parameter using the observational data sets. From the analysis of the jerk parameter, it is observed that, our derived model shows a marginal departure from the concordance $Λ$CDM model.

gr-qc↗

arXiv2021

Stability analysis of two-fluid dark energy models

In this paper, we have studied the stability of the cosmological models with dark energy and combination of matter fields and dark energy in an anisotropic space time. The pressure anisotropy along the spatial directions are derived and its stability in each direction has been examined. The four models presented here, show its stability on certain spatial direction. The role of matter field on the stability analysis has been obtained. The positive and negative value of cosmic string completely changed the stability behaviour of the model. The presence of a magnetic field disturbs the stability aspects of the models at least in an early epoch.

gr-qc↗

arXiv2020

Cosmological models with squared trace in modified gravity

In this work we present a few simple cosmological models under the modified theory of gravity in the particular form of $f(R,\mathcal{T})=R+2f(\mathcal{T})$, where $R$ is the Ricci Scalar and $\mathcal{T}$ is the trace of the energy-momentum tensor. Two special cosmological models are studied with (i) hyperbolic scale factor and (ii) specific form of the Hubble parameter. The models are observed to predict relevant cosmological parameters closer to the observational values. Both the models reduce to overlap with the $Λ$CDM model at late times. We have discussed some interesting results related to wormhole solutions as evolved from our model. The possible occurrence of Big Trip in wormholes for the models are also discussed.

gr-qc↗

arXiv2020

Constraining Nuclear Symmetry Energy parameters from Neutron skin thickness of $^{48}$Ca

In the present work, we use a finite range effective interaction to calculate the neutron skin thickness in $^{48}$Ca and correlate these quantities with the parameters of nuclear symmetry energy. Available experimental data on the neutron skin thickness in $^{48}$Ca are used to deduce information on the density slope parameter and the curvature symmetry parameter of the nuclear symmetry energy at saturation and at subsaturation densities. We obtained the constraints such as $54.5\leq L(ρ_0) \leq 97.5$ MeV and $47.3\leq L(ρ_c) \leq 57.1$ MeV for the density slope parameter. The constraints on the curvature symmetry energy parameter are obtained as $-170.7\leq K_{sym}(ρ_0) \leq -43.4$ MeV and $-80.8\leq K_{sym}(ρ_c) \leq 23.8$ MeV. A linear relation between the neutron skin thickness in $^{48}$Ca and in $^{2088}$Pb is obtained.

nucl-th↗