Abstract: In this talk I will present new constraints on U(1)Lμ−Lτ symmetry. In pulsar binaries, such U(1)Lμ−Lτ vectors induce an anomalously fast decay of the orbital period through the emission of dipole radiation. I’ll show the range of different pulsar binaries, finding the most powerful constraints for vector masses below O(10−18eV). 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. I 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 O(10−10eV). In both cases, the limits attainable with neutron stars reach gauge coupling g′≲10−20, which are many orders of magnitude stronger than previous constraints.

If I have time, I will also show very recent work on additional constraints on Li-Lj theories arising since they are coupled to a non-conserved current. Even though current conservation is only broken by the small neutrino masses and their mixing, we still find powerful bounds from muon decays, meson decays, neutrino decays, and unitarity that drastically shape the flavor lepton number gauge symmetry parameter space.