Radiation Fluid Stars in the Non-minimally Coupled $Y(R)F^2$ Gravity

TL;DR

This paper introduces a non-minimally coupled gravity model with electromagnetic fields to describe radiation fluid stars, deriving exact interior solutions and analyzing their physical properties, including mass-radius ratios and redshift limits.

Contribution

It presents a new exact solution framework for charged radiation fluid stars in Y(R)F^2 gravity, extending previous models with novel non-minimal coupling functions and boundary condition analysis.

Findings

Derived exact interior solutions for charged radiation stars.

Found mass-radius and redshift ratios slightly below classical bounds.

Established restrictions on physical parameters of charged compact stars.

Abstract

We propose a non-minimally coupled gravity model in $ Y(R)F^2 $ form to describe the radiation fluid stars which have the radiative equation of state between the energy density $ \rho $ and the pressure $p$ as $\rho=3p $. Here $F^2$ is the Maxwell invariant and $Y(R)$ is a function of the Ricci scalar $R$. We give the gravitational and electromagnetic field equations in differential form notation taking the infinitesimal variations of the model. We look for electrically charged star solutions to the field equations under a constraint which eliminating complexity of the higher order terms in the field equations. We determine the non-minimally coupled function $Y(R)$ and the corresponding model which admits new exact solutions in the interior of star and Reissner-Nordstrom solution at the exterior region. Using vanishing pressure condition at the boundary together with the continuity conditions of the metric functions and the electric charge, we find the mass-radius ratio, charge-radius ratio and gravitational surface redshift depending on the parameter of the model for the radiation fluid star. We derive general restrictions for the ratios and redshift of the charged compact stars. We obtain a slightly smaller upper mass-radius ratio limit than the Buchdahl bound $ 4/9 $ and a smaller upper redshift limit than the bound of the standard General Relativistic stars.