Neutron stars in f(mathtt {R,L_m}) gravity with realistic equations of state: joint-constrains with GW170817, massive pulsars, and the PSR J0030+0451 mass-radius from NICER data

R V Lobato,G A Carvalho,C A Bertulani

doi:10.1140/epjc/s10052-021-09785-3

Abstract

In this work, we investigate neutron stars (NS) in f(mathtt {R,L_m}) theory of gravity for the case f(mathtt {R,L_m})= mathtt {R}+ mathtt {L_m}+ sigma mathtt {R}mathtt {L_m}, where mathtt {R} is the Ricci scalar and mathtt {L_m} the Lagrangian matter density. In the term sigma mathtt {R}mathtt {L_m}, sigma represents the coupling between the gravitational and particles fields. For the first time the hydrostatic equilibrium equations in the theory are solved considering realistic equations of state and NS masses and radii obtained are subject to joint constrains from massive pulsars, the gravitational wave event GW170817 and from the PSR J0030+0451 mass-radius from NASA’s Neutron Star Interior Composition Explorer (NICER) data. We show that in this theory of gravity, the mass-radius results can accommodate massive pulsars, while the general theory of relativity can hardly do it. The theory also can explain the observed NS within the radius region constrained by the GW170817 and PSR J0030+0451 observations for masses around 1.4~M_{odot }.

Highlights

One attempt to explain the emerging issues is through modified theories of gravity
Using a set of fundamental nuclear matter equations of state (EoS) based on effective models of nuclear interactions and comparing the results with the gravitational-wave observations, as well as with massive pulsars in a joint constrain, the authors claim that the increment in the star mass is less than 1%
The neutron star mass-radius obtained with these EoS are subject to a joint constrain from observed massive pulsars, the gravitational wave events GW170817, and the PSR J0030+0451 mass-radius from NASA’s Neutron Star Interior Composition Explorer (NICER) data

Summary

Introduction

One attempt to explain the emerging issues is through modified theories of gravity. Many strategies were developed to get a theory beyond GR, some of them based on the change of the action, the Lagrangian density, or in the metric connection. Using a set of fundamental nuclear matter EoS based on effective models of nuclear interactions and comparing the results with the gravitational-wave observations, as well as with massive pulsars in a joint constrain, the authors claim that the increment in the star mass is less than 1%. The neutron star mass-radius obtained with these EoS are subject to a joint constrain from observed massive pulsars, the gravitational wave events GW170817, and the PSR J0030+0451 mass-radius from NASA’s Neutron Star Interior Composition Explorer (NICER) data.

Results

Conclusion