Neutron Star Structure in the Presence of Nonminimally Coupled Scalar Fields

TL;DR

This paper investigates how nonminimally coupled scalar fields influence neutron star structure, deriving mass-radius relations and constraining model parameters using observational data and comparing different scalar potentials.

Contribution

It provides new constraints on scalar-tensor theories with nonminimal coupling by analyzing neutron star properties across various potentials and equations of state.

Findings

Mass-radius relations depend on scalar field coupling and potential.

Constraints on the coupling parameter are derived from observational data.

The scalar field's central value is linked to its vacuum expectation value in Higgs-like potentials.

Abstract

We study the structure of neutron stars in scalar-tensor theories for the nonminimal coupling of the form $(1+\kappa \xi \phi^{2})\cal R$. We solve the hydrostatic equilibrium equations for two different types of scalar field potentials and three different equations of state representative of different degrees of stiffness. We obtain the mass-radius relations of the configurations and determine the allowed ranges for the term $\xi\phi^2$ at the center of the star and spatial infinity based on the measured maximum value of the mass for neutron stars and the recent constraints on the radius coming from gravitational wave observations. Thus we manage to limit the deviation of the model from general relativity. We examine the possible constraints on the parameters of the model and compare the obtained restrictions with the ones inferred from other cosmological probes that give the allowed ranges for the coupling constant only. In the case of the Higgs-like potential, we also find that the central value for the scalar field cannot be chosen arbitrarily but it depends on the vacuum expectation value of the field. Finally, we discuss the effect of the scalar field potential on the mass and the radius of the star by comparing the results obtained for the cases considered here.