Neutron Stars in f(R)-Gravity and Its Extension with a Scalar Axion Field

Artyom Astashenok,Sergey Odintsov

doi:10.3390/particles3030036

Abstract

We present a brief review of general results about non-rotating neutron stars in simple R 2 gravity and its extension with a scalar axion field. Modified Einstein equations are presented for metrics in isotropical coordinates. The mass–radius relation, mass profile and dependence of mass from central density on various equations of state are given in comparison to general relativity.

Highlights

Neutron stars are very interesting objects for the possible verification of physical models of dense matter but various theories of modified gravity
We present a brief review of general results about non-rotating neutron stars in simple R2 gravity and its extension with a scalar axion field
The mass–radius relation, mass profile and dependence of mass from central density on various equations of state are given in comparison to general relativity

Summary

Introduction

Neutron stars are very interesting objects for the possible verification of physical models of dense matter but various theories of modified gravity. The remaining 28%, clustered in galaxies and clusters of galaxies, consists of baryons (only 4%) and cold dark matter (CDM), the nature of which is unclear Another paradigm is the description of cosmological acceleration in frames of modified gravity [6,7,8]. This paper presents a brief review of general results about non-rotating neutron stars in simple R2 gravity and its extension with a scalar field. From a methodological point of view, we used metrics in isotropical coordinates for the deriving of modified Einstein equations In these coordinates, equations take relatively simple forms. For illustration we consider two equations of state (EoS) for nuclear matter—GM1 [18] and APR [19]

Basic Equations for Non-Rotating Stars in Isotropic Coordinates

R-Square Gravity with a Scalar Axion Field

Findings

Discussion of Results