Extreme neutron stars from Extended Theories of Gravity

TL;DR

This paper explores how extended theories of gravity, specifically $f(R)$ and $f( ext{G})$ models, can explain the existence of extremely massive neutron stars with strong magnetic fields, surpassing traditional mass limits.

Contribution

It demonstrates that cubic and quadratic corrections in $f(R)$ and $f( ext{G})$ gravity models can produce neutron stars with masses over 4 solar masses and high strangeness fractions, respectively.

Findings

Massive neutron stars with $M>4 M_{ ext{sun}}$ are possible with cubic $f(R)$ corrections.

Stable high-strangeness neutron stars can exist with quadratic $f( ext{G})$ corrections.

Magnetic fields in the star centers can reach $6-8 imes 10^{18}$ G.

Abstract

We discuss neutron stars with strong magnetic mean fields in the framework of Extended Theories of Gravity. In particular, we take into account models derived from $f(R)$ and $f(\cal G)$ extensions of General Relativity where functions of the Ricci curvature invariant $R$ and the Gauss-Bonnet invariant ${\cal G}$ are respectively considered. Dense matter in magnetic mean field, generated by magnetic properties of particles, is described by assuming a model with three meson fields and baryons octet. As result, the considerable increasing of maximal mass of neutron stars can be achieved by cubic corrections in $f(R)$ gravity. In principle, massive stars with $M> 4 M_{\odot}$ can be obtained. On the other hand, stable stars with high strangeness fraction (with central densities $\rho_{c}\sim 1.5-2.0$ GeV/fm$^{3}$) are possible considering quadratic corrections of $f(\cal {G})$ gravity. The magnetic field strength in the star center is of order $6-8\times 10^{18}$ G. In general, we can say that other branches of massive neutron stars are possible considering the extra pressure contributions coming from gravity extensions. Such a feature can constitute both a probe for alternative theories and a way out to address anomalous self-gravitating compact systems.