In this paper, we have emphasized the stability analysis of the accelerating cosmological models obtained in f(T) gravity theory. The behaviour of the models based on the evolution of the equation of state parameter shows phantom-like behaviour 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.
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 stars in the framework of ffalse(Qfalse)$f(Q)$ 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 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 masses beyond the 2M⊙$2 M_{\odot }$ without engaging of exotic matter. Therefore, the present study shows a new perception and physical significance about the exploration of ultra‐compact astrophysical objects.
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.
In this paper, we studied the bouncing behavior of the cosmological models formulated in the background of the Hubble function in the F(R,G) theory of gravity, where R and G, respectively, denote the Ricci scalar and Gauss–Bonnet invariant. The actions of the bouncing cosmology are studied with a consideration of the different viable models that 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. The phantom at the bounce epoch is analogous to quintessence behavior. Finally, we formulate the perturbed evolution equations and investigate the stability of the two bouncing solutions.
The ultimate fate of the Universe or the possible occurrence of future singularity to interpret the cosmic accelerating expansion phenomena has been discussed in this paper. The gravitational theory comprising of Ricci scalar R and Gauss-Bonnet invariant G, known as f (R, G) gravity has been considered in the quadratic form. Three models with the Hubble parameter that represents finite and infinite future time are presented. The physical and geometrical parameters of the models are analysed. Also, the properties of modified gravitational theory have been examined. The fate of the Universe evolution in this study confronts with neither little or pseudo rip nor the future singularity. The perturbed evolution equations are formulated in the scalar perturbation approach and the stability of the models are shown.
The dynamical system analysis of the cosmological models in f (T, T ) gravity, where T and T respectively represents the torsion scalar and trace of the energy-momentum tensor has been investigated. It demonstrates how first-order autonomous systems can be treated as cosmological equations and analyzed using standard dynamical system theory techniques. Two forms of the function f (T, T ) are considered (i) one with the product of trace and higher order torsion scalar and the other (ii) linear combination of linear trace and squared torsion. For each case, the critical points are derived and their stability as well the cosmological behaviours are shown. In both the models the stable critical points are obtained in the de-Sitter phase whereas in the matter and radiation dominated phase unstable critical points are obtained. At the stable critical points, the deceleration parameter shows the accelerating behaviour of the Universe whereas the equation of state parameter shows the ΛCDM behaviour. Finally the obtained Hubble parameter of the models are checked for the cosmological data sets.
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