arXiv subjects

S. K. Tripathy

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

At least 19 recordsLinked to original sources

arXiv2025

Logarithmic and Strong Coupling Models in Weyl-Type $f(Q,T)$ Gravity

In this paper, we have explored the cosmological implications of Weyl-type $f(Q,T)$ gravity, a modified gravitational theory formulated from Weyl geometry. The nonmetricity scalar $Q$ is coupled to the trace $T$ of the energy-momentum tensor. We analyze two models based on the logarithmic and strong coupling form of the function $f(Q,T)$. The corresponding field equations are then solved numerically after reformulating the system in terms of redshift. We used combined dataset from Cosmic Chronometers (CC), Pantheon$^+$ supernovae, and Baryon Acoustic Oscillations (BAO) and performed the Markov Chain Monte Carlo (MCMC) analysis to constrain the model parameters. Using the constrained parameters, the geometrical and dynamical aspects of the models are analyzed. The results successfully describe a transition from decelerated to accelerated expansion for both the models. The models mostly exhibit quintessence-like behavior and asymptotically approach the $Λ$CDM scenario at late times. The calculated age of the Universe from each model aligns with constraints from Planck and stellar age data. The violation of the strong energy condition and the satisfaction of null energy condition and dominant energy conditions are shown.

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arXiv2024

Non-minimally coupled teleparallel scalar field reconstruction of matter bounce scenario

Teleparallel description of gravity theories where the gravity is mediated through the tetrad field and consequent torsion provide an alternative route to explain the late time cosmic speed up issue. Generalization of the teleparallel gravity theory with different functional forms of the torsion scalar $T$ leads to $f(T)$ gravity. The role of scalar field played in addressing issues in cosmology and astrophysics has developed an interest in the inclusion of a scalar field along with an interaction potential in the action. Such a generalized gravity theory is dubbed as $f(T,ϕ)$ theory. We have explored such a gravity theory to reconstruct the interaction potential of the scalar field required for an extended matter bounce scenario. The cosmological implications of the reconstructed scalar field potential are studied considering two viable and well known functional forms of $f(T,ϕ)$. The energy conditions of these model are discussed to assess the viability of the cosmological models.

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arXiv2024

Matter Geometry Coupling and Casimir Wormhole Geometry

In this study, we investigate traversable wormhole solutions within the setup of $f(R,\mathcal{L}_{m})$ gravity, a modified theory of gravity where the gravitational action relies upon the matter Lagrangian $\mathcal{L}_{m}$ and the Ricci scalar $R$. In General Relativity (GR), stability issues in traversable wormholes necessitate the existence of exotic matter that violates the null energy condition (NEC). In contrast, we explore wormhole solutions that align with the criteria for Casimir wormholes, which do not necessarily require NEC violation. Our analysis demonstrates that in the context of $f(R,\mathcal{L}_{m})$ gravity, exotic matter can sustain these wormholes. We further examine the traversability conditions of the wormhole, considering both scenarios with and without the Generalized Uncertainty Principle (GUP) correction. Additionally, the stability of the wormhole is assessed based on equilibrium conditions. Our findings suggest that $f(R,\mathcal{L}_{m})$ gravity offers a viable framework for the existence of stable, traversable wormholes sustained by exotic matter, potentially expanding the landscape of viable wormhole solutions beyond the confines of GR.

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arXiv2024

Scalar field induced dynamical evolution in teleparallel gravity

In this paper, we investigate the role of scalar field potentials in the dynamical evolution of the Universe. A gravity theory with a non-minimally coupled scalar field with torsion in the geometrical action simulating effective dark energy is considered to study an extended matter bounce scenario. The dynamical behaviour of the equation of state parameter has been studied near the bouncing epoch. Keeping in mind the inflationary behaviour near the bounce, five different scalar field potential functions are explored, and their effect on the equation of state parameter is investigated.

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arXiv2024

Dynamical System Analysis for Scalar Field Potential in Teleparallel Gravity

In this paper, we have presented a power law cosmological model and its dynamical system analysis in $f(T,ϕ)$ gravity, where $T$ is the torsion scalar and $ϕ$ is the canonical scalar field. The two well-motivated forms of the non-minimal coupling function $F(ϕ)$, the exponential form and the power law form, with exponential potential function, are investigated. The dynamical system analysis is performed by establishing the dimensionless dynamical variables, and the critical points were obtained. The evolution of standard density parameters is analysed for each case. The behaviour of the equation of state (EoS) and deceleration parameter show agreement with the result of cosmological observations. The model parameters are constrained using the existence and the stability conditions of the critical points describing different epochs of the evolution of the Universe.

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arXiv2024

Baryon asymmetry constraints on Extended Symmetric Teleparallel Gravity

In this paper, we have explored the observed matter-antimatter asymmetry in the Universe to constrain the model parameters in extended symmetric teleparallel gravity (STG) or $f(Q,T)$ gravity, where $Q$ be the nonmetricity and $T$ be the trace of energy momentum tensor. We have considered two functional forms of $f(Q,T)$ to find the baryon asymmetry to entropy ratio calculated at a decoupling temperature. Two different data sets namely Hubble data set and the Hubble+BAO+Pantheon data sets are used to constrain the scale factor and the constrained model is used to obtain the baryon asymmetry to entropy ratio. It is observed that, model constrained from the Hubble data set favour a narrow range of the $f(Q,T)$ gravity parameters to reproduce the observed baryon asymmetry.

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arXiv2023

The Fate of the Universe Evolution in the Quadratic Form of Ricci-Gauss-Bonnet Cosmology

We investigate the possibility of future singularity due to the accelerating expansion of the Universe. It has been found that the gravitational theory comprises Ricci scalar $R$ and Gauss-Bonnet invariant $\mathcal{G}$, known as $F(R,\mathcal{G})$ gravity, which can be viewed in the quadratic form. Three models are presented using Hubble parameters to represent a finite and infinite future. The parameters of the models are analyzed on the basis of their physical and geometrical properties. This study also explores the properties of the modified gravitational theory, and neither the future singularity nor the little or pseudo rip is posed as threats to the fate of the Universe. We present scalar perturbation approaches to perturbed evolution equations and demonstrate their stability.

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arXiv2023

Constrained cosmological model in $f(Q,T)$ gravity with non-linear non-metricity

The $f(Q,T)$ cosmological model has emerged as a promising framework for understanding various aspects of cosmic evolution. In this study, we focused on obtaining the constraints of the free parameters in the non-linear form of non-metricity in $f(Q,T)$ gravity using the $Hubble$, $Pantheon$, and $BAO$ datasets. To determine the best-fit values for the model parameters and the equation of state (EoS) parameter, we employed an MCMC analysis. By examining the error bar plots, we observed that both the model curve and the $Λ$CDM curve successfully passed through the range obtained from the datasets. Additionally, we studied the state finder diagnostics and energy conditions to gain insights into the properties of the model. Furthermore, we conducted an analysis using the $Om(z)$ diagnostic, which provides a null test for the validity of the $Λ$CDM model.

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arXiv2023

Existence of non-exotic traversable wormholes in squared trace extended gravity theory

An extended gravity theory is used to explore the possibility of non-exotic matter traversable wormholes. In the extended gravity theory, additional terms linear and quadratic in the trace of the energy momentum tensor are considered in the Einstein-Hilbert action. Obviously, such an addition leads to violation of the energy-momentum tensor. The model parameters are constrained from the structure of the field equations. Non-exotic matter wormholes tend to satisfy the null energy conditions. We use two different traversable wormhole geometries namely an exponential and a power law shape functions to model the wormholes. From a detailed analysis of the energy conditions, it is found that, the existence of non-exotic matter traversable wormholes is not obvious in the model considered and its possibility may depend on the choice of the wormhole geometry. Also, we found that, non-exotic wormholes are possible within the given squared trace extended gravity theory for a narrow range of the chosen equation of state parameter.

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arXiv2023

Casimir wormhole with GUP correction in extended symmetric teleparallel gravity

Quantum mechanical concept such as the Casimir effect is explored to model traversable wormholes in an extended teleparallel gravity theory. The minimal length concept leading to the generalized uncertainty principle (GUP) is used to obtain the Casimir energy density. The effect of the GUP correction in the geometrical and physical properties of traversable Casimir wormholes are investigated. It is noted that the GUP correction has a substantial effect on the wormhole geometry and it modifies the energy condition. From a detailed calculation of the exotic matter content of the GUP corrected Casimir wormhole, it is shown that, a minimal amount of exotic matter is sufficient to support the stability of the wormhole.

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arXiv2023

Evolutionary behaviour of cosmological parameters with dynamical system analysis in f (Q, T) gravity

We have investigated the accelerating behaviour of the universe in $f(Q,T)$ gravity in an isotropic and homogeneous space-time. We have initially derive the dynamical parameters in the general form of $f(Q,T)=αQ^{m}+βT$ [Xu et al., Eur. Phys. J. C, \textbf{79}, 708 (2019)] and then split it into two cases (i) one with $m=1$ and the (ii) other with $β=0$. In the first case, it reduces to the linear form of the functional $f(Q,T)$ and second case leads to the higher power of the nonmetricity $Q$. In an assumed form of the hyperbolic scale factor, the models are constructed and its evolutionary behaviours are studied. The geometrical parameters as well the equation of state parameter are obtained and found to be in the preferred range of the cosmological observations. Marginal variation has been noticed in the behaviour of $ω$ and $ω_{eff}$ at present time. The violation of strong energy conditions in both the cases are shown. The dynamical system analysis for the models has been performed.

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arXiv2023

Observationally constrained accelerating cosmological model with higher power of non-metricity and squared trace

In this paper, a cosmological model of the Universe is presented in $f(Q,T)$ gravity and the parameters are constrained by cosmological data sets. Initially, a generalised form of $f(Q,T)$ model is used as $f(Q,T)=-λ_{1} Q^{m}-λ_{2} T^2$, where $λ_{1}$, $λ_{2}$ and $m$ are model parameters. With some algebraic manipulation, the Hubble parameter is obtained in terms of redshift. Then, using MCMC analysis, the model parameters are constrained using the most current Hubble and Pantheon$^{+}$ data. The model parameters are also verified through the BAO data set. The model shows an early deceleration transitioning to an accelerating phase of the Universe. The $Om(z)$ diagnostics indicate a positive slope, favouring the model to be in a phantom field dominated phase.

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arXiv2023

Bouncing cosmological models in a functional form of F(R) gravity

We have investigated some bouncing cosmological models in an isotropic and homogeneous space time with the F(R) theory of gravity. Two functional forms of F(R) have been investigated with a bouncing scale factor. The dynamical parameters are derived and analysed along with the cosmographic parameters. The analysis in both the models show the occurrence of bouncing scenario. The violation of strong energy conditions in both models is also shown. In the stability point of view we have analysed the behaviour of F_R = dF/dR with respect to cosmic time and both the models exhibit stable behaviour.

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arXiv2023

Evolution of Generalized Brans-Dicke parameter within a Superbounce scenario

We have studied a superbounce scenario in a set up of Brans-Dicke (BD) theory. The BD parameter is considered to be time dependent and is assumed to evolve with the Brans-Dicke scalar field. In the superbounce scenario, the model bounces at an epoch corresponding to a Big Crunch provided the ekpyrotic phase continues until that time. Within the given superbounce scenario, we investigate the evolution of the BD parameter for different equations of state. We chose an axially symmetric metric that has an axial symmetry along the x-axis. The metric is assumed to incorporate an anisotropic expansion effect. The effect of asymmetric expansion and the anisotropic parameter on the evolving and the non-evolving part of the BD parameter is investigated.

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arXiv2022

Bouncing cosmology in modified gravity with higher-order Gauss-Bonnet curvature term

In this paper, we have studied the bouncing behavior of the cosmological models formulated at the background of the Hubble function in the F(R, G) theory of gravity, where R and G denote the Ricci scalar and Gauss-Bonnet invariant. The actions of bouncing cosmology are studied under consideration of different viable models and can resolve the difficulty of singularity in standard Big-Bang cosmology. Both models show bouncing behavior and satisfy the bouncing cosmological properties. Models based on dynamical, deceleration, and energy conditions indicate the accelerating behavior at the late evolution time. Phantom at the bounce epoch is analogous to a quintessence behavior. Finally, we formulate the perturbed evolution equations and investigate the stability of two bouncing solutions.

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arXiv2022

Bouncing cosmological model with general relativistic hydrodynamics in extended gravity

In this paper, in an extended theory of gravity, we have presented bouncing cosmological model at the backdrop of an isotropic, homogeneous space-time, in presence of general relativistic hydrodynamics (GRH). The scale factor has been chosen in such a manner that with appropriate normalization, the quintom bouncing scenario can be assessed. Accordingly, the bounce occurs at $t=0$ and the corresponding Hubble parameter vanishes at the bounce epoch. The equation of state (EoS) parameter and the energy conditions of the model have been analysed. The violation of strong energy condition further supports the behaviour of extended gravity. As the bouncing cosmology suffers with instability, this model also shows the similar behaviour.

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arXiv2022

Dynamical features of $f(T,B)$ cosmology

In this paper, we have explored the field equations of $f(T,B)$ gravity and determined the dynamical parameters with the hyperbolic function of Hubble parameter. The accelerating behavior has been observed and the behavior of equation of state parameter indicates $ΛCDM$ model at late time. The role of model parameters in assessing the accelerating behavior has been emphasized. Interestingly the term containing $β$, the coefficient of boundary term, in the model parameter vanishes during the simplification. The scalar perturbation has been presented to show the stability of the model.

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arXiv2022

Dynamical Stability Analysis of Accelerating f(T) Gravity Models

In this paper, we have emphasized the stability analysis of the accelerating cosmological models obtained in $f(T)$ gravity theory. The behavior of the models based on the evolution of the equation of state parameter shows phantom-like behavior at the present epoch. The scalar perturbation technique is used to create the perturbed evolution equations, and the stability of the models has been demonstrated. Also, we have performed the dynamical system analysis for both the models. In the two specific $f(T)$ gravity models, three critical points are obtained in each model. In each model, at least one critical point has been observed to be stable.

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