Dynamical Chameleon Neutron Stars: stability, radial oscillations and scalar radiation in spherical symmetry

TL;DR

This paper investigates the stability and oscillation properties of chameleon-screened neutron stars in scalar-tensor theories, revealing deviations from general relativity and potential scalar radiation detectable by future gravitational-wave observatories.

Contribution

It provides the first non-linear simulations of neutron stars in chameleon screening, analyzing their stability, oscillation spectra, and scalar radiation during collapse.

Findings

Screened chameleon stars are stable against small radial oscillations.

Oscillation frequencies deviate from general relativity predictions.

Scalar fluxes during collapse could be detectable by future gravitational-wave detectors.

Abstract

Scalar-tensor theories whose phenomenology differs significantly from general relativity on large (e.g. cosmological) scales do not typically pass local experimental tests (e.g. in the solar system) unless they present a suitable "screening mechanism". An example is provided by chameleon screening, whereby the local general relativistic behavior is recovered in high density environments, at least in weak-field and quasi-static configurations. Here, we test the validity of chameleon screening in strong-field and highly relativistic/dynamical conditions, by performing fully non-linear simulations of neutron stars subjected to initial perturbations that cause them to oscillate or even collapse to a black hole. We confirm that screened chameleon stars are stable to sufficiently small radial oscillations, but that the frequency spectrum of the latter shows deviations from the general relativistic predictions. We also calculate the scalar fluxes produced during collapse to a black hole, and comment on their detectability with future gravitational-wave interferometers.