Neutron stars in generalized f(R) gravity

TL;DR

This paper explores neutron star models within a generalized quartic f(R) gravity theory, revealing that such stars can have arbitrary baryon numbers and differ significantly from standard models.

Contribution

It introduces a quartic gravity model with specific parameters and demonstrates through numerical integration that neutron stars can have unbounded baryon numbers in this framework.

Findings

Star mass increases then decreases with central density.

Baryon number increases monotonically with density.

Stars can have arbitrarily large baryon numbers in this theory.

Abstract

Quartic gravity theory is considered with the Einstein-Hilbert Lagrangean $R+aR^{2}+bR_{\mu \nu}R^{\mu \nu},$ $R_{\mu \nu}$ being Ricci\'s tensor and R the curvature scalar. The parameters $a$ and $b$ are taken of order 1 km$^{2}.$ Arguments are given which suggest that the effective theory so obtained may be a plausible approximation of a viable theory. A numerical integration is performed of the field equations for a free neutron gas. As in the standard Oppenheimer-Volkoff calculation the star mass increases with increasing central density until about 1 solar mass and then decreases. However a dramatic difference exists in the behaviour of the baryon number, which increases monotonically. The calculation suggests that the theory allows stars in equilibrium with arbitrary baryon number, no matter how large.