In the present work we have searched the existence of the late time acceleration of the Universe. The matter source that is responsible for the late time acceleration of the Universe consists of cosmic fluid with the equation of state parameter $\omega =\frac{p}{\rho}$ and uniform magnetic field of energy density $\rho_{B}$. The study is done here under the framework of spatially homogeneous and anisotropic locally rotationally symmetric (LRS) Bianchi-I cosmological model in the presence of magnetized dark energy. To get the deterministic model of the Universe, we assume that the shear scalar $(\sigma)$ in the model is proportional to expansion scalar $(\theta)$. This condition leads to $A=B^{n}$, where $A$ and $B$ are metric functions and $n$ is a positive constant giving the proportionality condition between shear and expansion scalar. It has been found that the isotropic distribution of magnetized dark energy leads to the present accelerated expansion of the Universe and the derived model is in good agreement with the recent astrophysical observations. The physical behavior of the Universe has been discussed in details.

Magnetized dark energy and the late time acceleration

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. 

/pdf/matter-bounce-scenario-in-extended-symmetric-teleparallel-3n5citvm.pdf

Matter bounce scenario in extended symmetric teleparallel gravity

Our current investigation is inherently linked to the observations of gravitational waves from the GW190814 event which suggests that the source of the signals can be ascribed to a compact binary coalescence of a 22.2 to 24.3M ⊙ black hole and a compact object endowed with a mass of 2.50 to 2.67M ⊙. In the current exposition, we are concerned with modeling of the lower mass component of the coalescence pair. We utilize the f(𝒬) gravity together with the Minimal Geometric Deformation (MGD) technique to obtain compact stellar objects with masses aligned with the GW190814 event. Starting off with the Tolman IV ansatz for one of the metric functions, together with an MIT Bag model equation of state we are able to reduce the problem of fully describing the gravitational behavior of the seed solution to a quadrature. Through the MGD technique, we introduce anisotropy by deforming the radial part of the gravitational potential. This enables us to obtain two new classes of solutions which depend on the metricity parameter, 𝒬 and the deformation constant, β. We show that these two parameters play a crucial role in determining the thermodynamical behavior and stability of our models. In particular, we show that the interplay between the metricity parameter and the deformation constant predicts the mass of the progenitor articulating as the secondary component of GW190814.

/pdf/exploring-physical-properties-of-minimally-deformed-strange-w5emwkc3.pdf

Exploring physical properties of minimally deformed strange star model and constraints on maximum mass limit in f(𝒬) gravity

In this article, we find the possibility of generalized wormhole formation in the galactic halo due to dark matter using observational data within the matter coupling gravity formalism. Keeping this as a target, we specifically employ f(R, T) gravity with (i) a variational approach concerning the metric, and (ii) the anisotropic source of matter. To understand the features of the wormholes, we thoroughly calculated and analyzed the energy conditions under f(R, T) gravity. We discuss the second embedded wormhole solution, known as the generalized Ellis–Bronnikov spacetime (ultrastatic wormhole model), in terms of the tortoise coordinate. Thereafter we generate and compare different wormhole solutions depending on the parametric values. In the second part of our investigation, we presented dark matter halos and provided interesting features by considering a couple of profiles. For the dark matter halos models, we particularly use the observational data of the M87 galaxy and the Milky Way galaxy.

On the Possibility of Generalized Wormhole Formation in the Galactic Halo Due to Dark Matter Using the Observational Data within the Matter Coupling Gravity Formalism

Abstract 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 has been 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. 

/pdf/role-of-extended-gravity-theory-in-matter-bounce-dynamics-t32i3hgw.pdf

Role of extended gravity theory in matter bounce dynamics

In this article, we present and analyze cosmological models with an anisotropic variable parameter. We have set up the field equations with the space time in the form of Bianchi I metric with an f(R, T) gravity. The functional form for the f(R, T) gravity has been assumed to be $$f(R,T)=R+2f(T)$$
 , where R and T are, respectively, the Ricci scalar and trace of the energy–momentum tensor. Two different models are constructed with respect to the scale factors, such as power law scale factor and hybrid scale factor. Moreover, the anisotropic parameter taken here in the form of hyperbolic function further gives clarity on the behavior of equation of state parameter. It is to note that when the values of the coefficient constant vanish, the model yields the isotropic universe. For both the cases, the deceleration parameter, state finder diagnostic pair and energy conditions have been obtained and analyzed which provide physical plausibility of the models.

F. Esmeili

Papers

Cosmological models with variable anisotropic parameter in f(R, T) gravity