S. I. dos Santos Jr. | Searcharxiv

arXiv2020

Hydrostatic equilibrium configurations of neutron stars in a non-minimal geometry-matter coupling theory of gravity

In this work we analyze hydrostatic equilibrium configurations of neutron stars in a non-minimal geometry-matter coupling (GMC) theory of gravity. We begin with the derivation of the hydrostatic equilibrium equations for the $f(R,L) $ gravity theory, where $R$ and $L$ are the Ricci scalar and Lagrangian of matter, respectively. We assume $f(R,L)=R/2+[1+σR]L$, with $σ$ constant. To describe matter inside neutron stars we assume the polytropic equation of state $p=K ρ^γ$, with $K$ and $γ= 5/3 $ being constants. We show that in this theory it is possible to reach the mass of massive pulsars such as PSR J2215+5135. As a feature of the GMC theory, very compact neutron stars with radius $\sim8$km and $M\sim 2.6M_\odot$ are stable, thus surpassing the Buchdal and Schwarzschild radius limits. Moreover, the referred stellar diameter is obtained within the range of observational data.

gr-qc↗

arXiv2019

A conservative energy-momentum tensor in the $f(R,T)$ gravity and its implications for the phenomenology of neutron stars

The solutions for the Tolmann-Oppenheimer-Volkoff (TOV) equation bring valuable informations about the macroscopical features of compact astrophysical objects as neutron stars. They are sensitive to both the equation of state considered for nuclear matter and the background gravitational theory. In this work we construct the TOV equation for a conservative version of the $f(R,T)$ gravity. While the non-vanishing of the covariant derivative of the $f(R,T)$ energy-momentum tensor yields, in a cosmological perspective, the prediction of creation of matter throughout the universe evolution as shown by T. Harko, in the analysis of the hydrostatic equilibrium of compact astrophysical objects, this property still lacks a convincing physical explanation. The imposition of $\nabla^μT_{μν}=0$ demands a particular form for the function $h(T)$ in $f(R,T)=R+h(T)$, which is here derived. Therefore, the choice of a specific equation of state for the star matter demands a unique form of $h(T)$, manifesting a strong connection between conserved $f(R,T)$ gravity and the star matter constitution. We construct and solve the TOV equation for the general equation of state for $p=kρ^Γ$, with $k$ being the EoS parameter, $ρ$ {\it the energy density} and $Γ$ is the adiabatic index. We also derive the macroscopical properties of neutron stars ($Γ=5/3$) within this approach.

gr-qc↗