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Register a new userAnisotropic compact stars in $f(R)$ gravity
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We derive a new interior solution for stellar compact objects in $fmathcal{(R)}$ gravity assuming a differential relation to constrain the Ricci curvature scalar. To this aim, we consider specific forms for the radial component of the metric and the first derivative of $fmathcal{(R)}$. After, the time component of the metric potential and the form of $f(mathcal R)$ function are derived. From these results, it is possible to obtain the radial and tangential components of pressure and the density. The resulting interior solution represents a physically motivated anisotropic neutron star model. It is possible to match it with a boundary exterior solution. From this matching, the components of metric potentials can be rewritten in terms of a compactness parameter $C$ which has to be $C=2GM/Rc^2 <<0.5$ for physical consistency. Other physical conditions for real stellar objects are taken into account according to the solution. We show that the model accurately bypasses conditions like the finiteness of radial and tangential pressures, and energy density at the center of the star, the positivity of these components through the stellar structure, and the negativity of the gradients. These conditions are satisfied if the energy-conditions hold. Moreover, we study the stability of the model by showing that Tolman-Oppenheimer-Volkoff equation is at hydrostatic equilibrium. The solution is matched with observational data of millisecond pulsars with a withe dwarf companion and pulsars presenting thermonuclear bursts.
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In this study, we present a generalized spherically symmetric, anisotropic and static compact stellar model in $f(T)$ gravity, where $T$ represents the torsion scalar. By employing the Karmarkar condition we have obtained embedding class 1 metric from the general spherically metric of class 2 and the solutions of the Einstein field equations (EFE) has been presented with the choice of suitable parametric values of $n$ under a simplified linear form of $f(T)$ gravity reads as $f(T)=A+BT$, where $A$ and $B$ are two constants. By matching the interior spacetime metric with the exterior Schwarzschild metric at the surface and considering the values of mass and radius of the compact stars we obtain the values of the unknown constants. We have presented further a detailed analysis of the physical acceptability and examined the stability of the stellar configuration by studying the energy conditions, generalized Tolman-Oppenheimer-Volkov (TOV) equation, Herrera cracking concept, adiabatic index, etc. In the investigation, we predict numerical values of the central density, surface density, central pressure, etc., in a tabular form taking different values of $n$ specifically for $LMC~X-4$, $Cen~X-3$ and $SMC~X-1$ as the representative of compact star candidates.
In this paper, we employ mimetic $f(R,T)$ gravity coupled with Lagrange multiplier and mimetic potential to yield viable inflationary cosmological solutions consistent with latest Planck and BICEP2/Keck Array data. We present here three viable inflationary solutions of the Hubble parameter ($H$) represented by $H(N)=left(A exp beta N+B alpha ^Nright)^{gamma }$, $H(N)=left(A alpha ^N+B log Nright)^{gamma }$, and $H(N)=left(A e^{beta N}+B log Nright)^{gamma }$, where $A$, $beta$, $B$, $alpha$, $gamma$ are free parameters, and $N$ represents the number of e-foldings. We carry out the analysis with the simplest minimal $f(R,T)$ function of the form $f(R,T)= R + chi T$, where $chi$ is the model parameter. We report that for the chosen $f(R,T)$ gravity model, viable cosmologies are obtained compatible with observations by conveniently setting the Lagrange multiplier and the mimetic potential.
In this paper, we study the stellar structure in terms of alternative theory of gravity specially by f (R;T) gravity theory. Here, we consider the function f (R;T) = R+2VT where R is the Ricci scalar, T is the stress-energy momentum and V is the coupling constant. Using it we developed a stellar model that briefly explains the isotropic matter distribution within the compact object filled with perfect fluid. The stability of the model is shown by several physical and stability conditions. With the accecptibility of our theory, we were able to collect data for compact stars like PSR-B0943+10, CEN X-3, SMC X-4, Her X-1 and 4U1538-52 with great accuracy.
In this article we study the hydrostatic equilibrium configuration of neutron stars (NSs) and strange stars (SSs), whose fluid pressure is computed from the equations of state $p=omegarho^{5/3}$ and $p=0.28(rho-4{cal B})$, respectively, with $omega$ and ${cal B}$ being constants and $rho$ the energy density of the fluid. We also study white dwarfs (WDs) equilibrium configurations. We start by deriving the hydrostatic equilibrium equation for the $f(R,T)$ theory of gravity, with $R$ and $T$ standing for the Ricci scalar and trace of the energy-momentum tensor, respectively. Such an equation is a generalization of the one obtained from general relativity, and the latter can be retrieved for a certain limit of the theory. For the $f(R,T)=R+2lambda T$ functional form, with $lambda$ being a constant, we find that some physical properties of the stars, such as pressure, energy density, mass and radius, are affected when $lambda$ is changed. We show that for some particular values of the constant $lambda$, some observed objects that are not predicted by General Relativity theory of gravity can be attained. Moreover, since gravitational fields are smaller for WDs than for NSs or SSs, the scale parameter $lambda$ used for WDs is small when compared to the values used for NSs and SSs.
Torsion and nonmetricity are inherent ingredients in modifications of Einteins gravity that are based on affine spacetime geometries. In the context of pure f(R) gravity we discuss here, in some detail, the relatively unnoticed duality between torsion and nonmetricity. In particular we show that for R2 gravity torsion and nonmetricity are related by projective transformations. Since the latter correspond simply to redefining the affine parameters of autoparallels, we conclude that torsion and nonmetricity are physically equivalent properties of spacetime. As a simple example we show that both torsion and nonmetricity can act as geometric sources of accelerated expansion in a spatially homogenous cosmological model within R2 gravity and we brie y discuss possible implications of our results.
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