Spontaneous Scalarization with Massive Fields

TL;DR

This paper investigates how adding a mass term to the scalar field affects spontaneous scalarization in neutron stars, potentially avoiding observational constraints and leading to observable astrophysical signatures.

Contribution

It introduces a massive scalar field extension to spontaneous scalarization models, analyzing parameter ranges compatible with current observations and exploring observable effects.

Findings

Mass term allows scalarization to evade binary system constraints.

Scalarization can produce strong, observable effects in neutron star mergers.

Allowed parameter space includes nonperturbative scalarization effects.

Abstract

We study the effect of a mass term in the spontaneous scalarization of neutron stars, for a wide range of scalar field parameters and neutron star equations of state. Even though massless scalars have been the focus of interest in spontaneous scalarization so far, recent observations of binary systems rule out most of their interesting parameter space. We point out that adding a mass term to the scalar field potential is a natural extension to the model that avoids these observational bounds if the Compton wavelength of the scalar is small compared to the binary separation. Our model is formally similar to the asymmetron scenario recently introduced in application to cosmology, though here we are interested in consequences for neutron stars and thus consider a mass term that does not modify the geometry on cosmological scales. We review the allowed values for the mass and scalarization parameters in the theory given current binary system observations and black hole spin measurements. We show that within the allowed ranges, spontaneous scalarization can have nonperturbative, strong effects that may lead to observable signatures in binary neutron star or black hole-neutron star mergers, or even in isolated neutron stars.