Universal relations for quasinormal modes of neutron stars in R2 gravity

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 ultralong lived and, for the lower scalar masses, their frequencies are inversely proportional to the corresponding Compton wavelength.