Probing muonic forces with neutron star binaries

TL;DR

This paper demonstrates how gravitational wave observations from neutron star binaries can be used to detect or constrain long-range muonic forces, especially those arising from a gauged U(1)$_{L___ au}$ symmetry, providing much stronger limits than previous methods.

Contribution

It introduces a novel method to probe muonic forces via gravitational waves from neutron star binaries, offering the most stringent constraints to date on light vector bosons coupled to muons.

Findings

Current data can detect light vectors with masses below 10^{-10} eV.

Neutron star binaries can set constraints on gauge coupling g' down to 10^{-20}.

Next-generation detectors will significantly improve sensitivity to muonic forces.

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 U(1)$_{L_\mu - L_\tau}$ symmetry. In pulsar binaries, such U(1)$_{L_\mu - L_\tau}$ 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 ${\cal O}(10^{-18} {\rm eV})$. 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 ${\cal O}(10^{-10} {\rm eV})$. In both cases, the limits attainable with neutron stars reach gauge coupling $g^\prime\lesssim 10^{-20}$, 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.