Newtonian and Post Newtonian Expansionfree Fluid Evolution in f(R) Gravity

TL;DR

This paper investigates the evolution and stability of an anisotropic, adiabatic fluid sphere undergoing collapse in $f(R)$ gravity, focusing on Newtonian and post-Newtonian regimes and how instability depends on physical parameters.

Contribution

It analyzes the instability conditions of expansionfree fluid collapse in $f(R)$ gravity using perturbation methods, considering a specific $f(R)$ model with Schwarzschild solution.

Findings

Instability depends on pressure anisotropy and energy density.

Conditions are influenced by constraints from $f(R)$ gravity.

Newtonian and post-Newtonian regimes are analyzed.

Abstract

We consider a collapsing sphere and discuss its evolution under the vanishing expansion scalar in the framework of $f(R)$ gravity. The fluid is assumed to be locally anisotropic which evolves adiabatically. To study the dynamics of the collapsing fluid, Newtonian and post Newtonian regimes are taken into account. The field equations are investigated for a well-known $f(R)$ model of the form $R+\delta R^2$ admitting Schwarzschild solution. The perturbation scheme is used on the dynamical equations to explore the instability conditions of expansionfree fluid evolution. We conclude that instability conditions depend upon pressure anisotropy, energy density and some constraints arising from this theory.