Spontaneous Scalarization in Scalar-Tensor Theories with Conformal Symmetry as an Attractor

TL;DR

This paper explores a new class of scalar-tensor theories with conformal symmetry acting as a cosmological attractor, leading to spontaneous scalarization in neutron stars, with implications for observational constraints.

Contribution

Introduces a one-parameter family of scalar-tensor theories with conformal symmetry as an attractor, extending constant-G theory and analyzing neutron star structures.

Findings

Effective scalar coupling aligns with quadratic model predictions.

Constraints from pulsar-timing measurements apply broadly to curvature parameters.

Model demonstrates spontaneous scalarization consistent with observational bounds.

Abstract

Motivated by constant-G theory, we introduce a one-parameter family of scalar-tensor theories as an extension of constant-G theory in which the conformal symmetry is a cosmological attractor. Since the model has the coupling function of negative curvature, we expect spontaneous scalarization occurs and the parameter is constrained by pulsar-timing measurements. Modeling neutron stars with realistic equation of states, we study the structure of neutron stars and calculate the effective scalar coupling with the neutron star in these theories. We find that within the parameter region where the observational constraints are satisfied, the effective scalar coupling almost coincides with that derived using the quadratic model with the same curvature. This indicates that the constraints obtained by the quadratic model will be used to limit the curvature of the coupling function universally in the future.