Universal relations for quasinormal modes of neutron stars in $R^2$ gravity

TL;DR

This paper derives universal relations for quasinormal modes of neutron stars in $R^2$ gravity, focusing on scalar field effects and different matter compositions, revealing long-lived dipole modes with frequency dependence on scalar mass.

Contribution

It introduces universal relations for neutron star quasinormal modes in $R^2$ gravity considering various equations of state and scalar masses, highlighting the properties of dipole F-modes.

Findings

Dipole F-modes are ultra-long lived.

Frequencies of dipole F-modes inversely proportional to scalar Compton wavelength.

Universal relations hold across different matter compositions.

Abstract

We construct quasinormal modes for neutron stars in $R^2$ gravity in the Einstein frame, considering scalar masses in the sub-neV range. In particular, we investigate the fundamental quadrupole fluid f-modes and the dipole fluid F-modes. Employing six equations of state covering matter content with nucleons, hyperons, and quarks, we then propose universal relations for the quadrupole f-modes and dipole F-modes. The dipole F-modes are ultra-long lived and, for the lower scalar masses, their frequencies are inversely proportional to the corresponding Compton wavelength.