Neutron Star Bounds on Muonic Fifth Forces from Picometer to Kilometer Scales

Abstract

Experimental searches for fifth forces coupled to muons are fundamentally limited by the scarcity of muons in ordinary matter, whereas neutron stars contain abundant muon populations. We show that these compact objects therefore provide superior sensitivity across a broad range of mediator masses. Neutron-star cooling implies limits of $g_{\varphi \mu }\lesssim 10^{-12}$ and $g_{V\mu }\lesssim 3\times 10^{-13}$ on scalar and vector bosons with masses $m_X\lesssim 100$ keV, whereas SN 1987A cooling implies only $g\lesssim 3\times 10^{-9}$. Moreover, hydrostatic equilibrium requires any long-range muonic force to be sufficiently weak, surpassing cooling bounds for $m_X\lesssim 10^{-5}$ eV. Together, these observables provide the most stringent probes of muonic interactions over distance scales ranging from picometers to kilometers.

Comments: 5 pages, 3 figures, 1 table + 1 page, 1 figure (End Matter) + 3 pages (Supplemental Material)