arXiv subjects

B. Mishra

Publications and source records attributed to B. Mishra.

At least 91 records · Page 5Linked to original sources

arXiv2023

Matter Bounce Scenario in Extended Symmetric Teleparallel Gravity

In this paper, we have shown the matter bounce scenario of the Universe in an extended symmetric teleparallel gravity, the f(Q) gravity. Motivated from the bouncing scenario and loop quantum cosmology (LQC), the form of the function $f(Q)$ has been obtained at the backdrop of Friedmann-Lemaitre-Robertson Walker (FLRW) space time. Considering the background cosmology dominated by dust fluid, the e-folding parameter has been expressed, which contains the nonmetricity term. Since the slow roll criterion in the bouncing context is not valid, we used a conformal equivalence between f(Q) and scalar-tensor model to apply the bottom-up reconstruction technique in the bouncing model. The dynamics of the model has been studied through the phase space analysis, where both the stable and unstable nodes are obtained. Also, the stability analysis has been performed with the first order scalar perturbation of the Hubble parameter and matter energy density to verify the stability of the model.

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arXiv2023

Dynamical systems analysis in $f(T,ϕ)$ gravity

Teleparallel based cosmological models provide a description of gravity in which torsion is the mediator of gravitation. Several extensions have been made within the so-called Teleparallel equivalent of general relativity which is equivalent to general relativity at the level of the equations of motion where attempts are made to study the extensions of this form of gravity and to describe more general functions of the torsion scalar $T$. One of these extensions is $f(T,ϕ)$ gravity; $T$ and $ϕ$ respectively denote the torsion scalar and scalar field. In this work, the dynamical system analysis has been performed for this class of theories to obtain the cosmological behaviour of a number of models. Two models are presented here with some functional form of the torsion scalar and the critical points are obtained. For each critical point, the stability behaviour and the corresponding cosmology are shown. Through the graphical representation the equation of state parameter and the density parameters for matter-dominated, radiation-dominated and dark energy phase are also presented for both the models.

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arXiv2022

Analyzing the geometrical and dynamical parameters of modified Teleparallel-Gauss-Bonnet model

To recreate the cosmological models, we employed the parametrization approach in modified teleparallel Gauss-Bonnet gravity. It has been interesting to apply the parametrization approach to investigate cosmological models. The real benefit of using this method is that the observational data may be incorporated to examine the cosmological models. Several cosmological parameters were examined, such as the Hubble parameter (H), the deceleration parameter (q), and the equation of state (EoS) parameter (w). The results obtained are consistent with recent cosmological findings in the conventional scenario. A transition scenario from a decelerating stage to an accelerating stage of cosmic evolution has been observed. The EoS parameter is also in the quintessence phase, which drives the accelerating expansion of the Universe. Also, we look at the violation of strong energy condition, which has become inevitable in the context of modified gravitational theory. Finally, we have performed the Om(z) diagnostic and also obtained the age of the Universe by using the data from the cosmological observations.

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arXiv2022

Minimally deformed wormholes inspired by noncommutative geometry

In this article, new wormhole solutions in the framework of General Relativity are presented. Taking advantage of gravitational decoupling by means of minimal geometric deformation approach and, the so-called noncommutative geometry Gaussian and Lorentzian density profiles, the seminal Morris-Thorne space-time is minimally deformed providing new asymptotically wormhole solutions. Constraining the signature of some parameters, the dimensionless constant $α$ is bounded using the flare-out and energy conditions. In both cases, this results in an energy-momentum tensor that violates energy conditions, thus the space-time is threading by exotic matter. However, it is possible to obtain a positive defined density at the wormhole throat and its neighborhood. To further support the study a thoroughly graphical analysis has been performed.

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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

Teleparallel scalar-tensor gravity through cosmological dynamical systems

Scalar-tensor theories offer the prospect of explaining the cosmological evolution of the Universe through an effective description of dark energy as a quantity with a non-trivial evolution. In this work, we investigate this feature of scalar-tensor theories in the teleparallel gravity context. Teleparallel gravity is a novel description of geometric gravity as a torsional-rather than curvature-based quantity which presents a new foundational base for gravity. Our investigation is centered on the impact of a nontrivial input from the kinetic term of the scalar field. We consider a number of model settings in the context of the dynamical system to reveal their evolutionary behavior. We determine the critical points of these systems and discuss their dynamics.

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arXiv2022

Anisotropic Strange Star Model Beyond Standard Maximum Mass Limit by Gravitational Decoupling in $f(Q)$ Gravity

The current theoretical development identified as the gravitational decoupling via Complete Geometric Deformation (CGD) method that has been introduced to explore the nonmetricity $Q$ effects in relativistic astrophysics. In the present work, we have investigated the gravitationally decoupled anisotropic solutions for the strange star in the framework of $f(Q)$ gravity by utilizing the CGD technique. To do this, we started with Tolman metric ansatz along with the MIT Bag model equation of state related to the hadronic matter. The solutions of the governing equations of motions are obtained by using two approaches, namely the mimicking of the $θ$ sector to the seed radial pressure and energy density of the fluid model. The obtained models describe the self-gravitating static, compact objects whose exterior solution can be given by the vacuum Schwarzschild Anti-de Sitter spacetime. In particular, we modeled five stellar candidates, viz., LMC X-4, PSR J1614-2230, PSR J0740+6620, GW190814, and GW 170817 by using the observational data. The rigorous viability tests of the solutions have been performed through regularity and stability conditions. We observed that the nonmetricity parameter and decoupling constant show a significant effect on stabilizing to ensure the physically realizable stellar models. The innovative feature of this work is to present the stable compact objects with the masses beyond the $2 M_{\odot}$ without engaging of exotic matter. Therefore, the present study shows a new perception and physical significance about the exploration of ultra-compact astrophysical objects.

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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

f(R) wormholes embedded in a pseudo--Euclidean space $E^{5}$

This work is devoted to the study of analytic wormhole solutions within the framework of $f(R)$ gravity theory. To check the possibility of having wormhole structures satisfying energy conditions, by means of the class I approach the pair $\{Φ(r), b(r)\}$ describing the wormhole geometry has been obtained. Then, in conjunction with a remarkably $f(R)$ gravity model, the satisfaction of the null and weak energy conditions at the wormhole throat and its neighborhood is investigated. To do so, some constant parameters have been bounded restricting the space parameter. In this concern, the $f(R)$ gravity model and its derivatives are playing a major role, specially in considering the violation of the non--existence theorem. Furthermore, the shape function should be bounded from above by the Gronwall--Bellman shape function, where the red--shift function plays a relevant role. By analyzing the main properties at the spatial stations and tidal accelerations at the wormhole throat, possibilities and conditions for human travel are explored.

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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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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.

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arXiv2022

Anisotropic stars in modified gravity: An extended gravitational decoupling approach

In the work, we present investigation on decoupling gravitational sources under the framework of $f(R,T)$ gravity. Basically the complete geometric deformation technique has been employed here which facilitates finding exact solutions to the anisotropic astrophysical system smoothly without imposing any particular ansatz for deformation function. Along with this we have also used 5-dimensional Euclidean spacetime in order to describe the embedding Class I spacetime for getting a solvable spherical physical system. The solutions thus obtained show physically interesting as well as viable with new possibilities to sought for. Especially, from the present investigation it is worthy to note that the mixture $f(R,T)$ + CGD translate the scenario beyond the pure GR realm and hence clearly helps to enhance the features of the interior astrophysical aspects of compact stellar objects. Therefore to check the physical acceptability and stability of the stellar system based on the obtained solutions, we have performed a few physical tests which satisfy all the stability criteria, including nonsingular nature of the density as well as pressure.

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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.

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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.

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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.

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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.

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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.

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