Neutron stars in general second order scalar-tensor theory: the case of non-minimal derivative coupling

TL;DR

This paper explores neutron star solutions within a specific scalar-tensor gravity theory, showing that such stars can have different internal structures while maintaining standard external geometry, and constrains the model parameters for astrophysical viability.

Contribution

The study constructs neutron star models in a non-minimal derivative coupling scalar-tensor theory, demonstrating their compatibility with observations and extending understanding of alternative gravity theories.

Findings

Neutron stars can have different internal structures in this theory.

External geometry remains Schwarzschild, matching general relativity predictions.

Model parameters are constrained to ensure astrophysical viability.

Abstract

We consider the sector of Horndeski's gravity characterized by the coupling between the kinetic scalar field term and the Einstein tensor. We numerically construct neutron star configurations where the external geometry is identical to the Schwarzschild metric but the interior structure is considerably different from standard general relativity. We constrain the only parameter of this model from the requirement that compact configurations exist, and we argue that solutions less compact than neutron stars, such as white dwarfs, are also supported. Therefore, our model provides an explicit modification of general relativity that is astrophysically viable and does not conflict with Solar System tests.