Probing muonic forces with neutron star binaries
Jeff A. Dror, Ranjan Laha, Toby Opferkuch
Abstract
We show that gravitational wave emission from neutron star binaries can be used to discover any generic long-ranged muonic force due to the large inevitable abundance of muons inside neutron stars. As a minimal consistent example, we focus on a gauged ${\mathrm{U}(1)}_{{L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}}$ symmetry. In pulsar binaries, such ${\mathrm{U}(1)}_{{L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}}$ vectors induce an anomalously fast decay of the orbital period through the emission of dipole radiation. We study a range of different pulsar binaries, finding the most powerful constraints for vector masses below $\mathcal{O}({10}^{\ensuremath{-}18}\text{ }\text{ }\mathrm{eV})$. For merging binaries, the presence of muons in neutron stars can result in dipole radiation as well as a modification of the chirp mass during the inspiral phase. We make projections for a prospective search using both the GW170817 and S190814bv events and find that current data can discover light vectors with masses below $\mathcal{O}({10}^{\ensuremath{-}10}\text{ }\text{ }\mathrm{eV})$. In both cases, the limits attainable with neutron stars reach gauge coupling ${g}^{\ensuremath{'}}\ensuremath{\lesssim}{10}^{\ensuremath{-}20}$, which are many orders of magnitude stronger than previous constraints. We also show projections for next generation experiments, such as Einstein Telescope and Cosmic Explorer.