Neutron stars in degenerate higher-order scalar-tensor theories: Axial perturbations

TL;DR

This paper investigates how axial perturbations and quasi-normal modes of neutron stars are affected in a specific class of Degenerate Higher-Order Scalar-tensor theories, revealing deviations from general relativity in frequencies and damping times.

Contribution

It derives the quadratic action for axial perturbations in DHOST theories and analyzes the resulting quasi-normal modes, highlighting deviations from GR and effects on universal relations.

Findings

Deviations in QNM frequencies and damping times compared to GR.

Modified gravity parameter influences universal relations.

Neutron star configurations are consistent within the DHOST framework.

Abstract

We study the axial (or odd-parity) perturbations of neutron stars in a one-parameter subclass of Degenerate Higher-Order Scalar-tensor (DHOST) theories. After recalling the equilibrium neutron star configurations obtained in a previous work by solving the generalised Tolman-Oppenheimer-Volkoff equations in DHOST theories, we derive the action at quadratic order in linear perturbations of axial type. We then compute the quasi-normal modes (QNMs) for several values of the modified gravity parameter and various equations of state, observing deviations of both frequencies and damping times with respect to general relativity. We also analyze the impact of our modified gravity parameter on the universal relations relating the (rescaled) frequencies and damping times to the compactness of the neutron star.