Using neutron stars to probe dark matter charged under a $L_\mu-L_\tau$ symmetry

TL;DR

This paper explores how neutron star heating caused by dark matter particles charged under a $L__-L__$ symmetry can serve as a novel probe for weakly interacting dark matter in the 100 MeV to 100 GeV mass range, especially when traditional detection methods are ineffective.

Contribution

It introduces a relativistic model of dark matter capture in neutron stars considering a $L__-L__$ charged fermion, revealing new parameter space accessible through neutron star heating observations.

Findings

Neutron star heating can probe dark matter masses from 100 MeV to 100 GeV.

Loop-induced interactions with quarks and electrons are weak, but muon interactions enable effective star heating.

Observations of old cold neutron stars can explore previously untested dark matter parameter space.

Abstract

Kinetic heating of old cold neutron stars, via the scattering of dark matter with matter in the star, provides a promising way to probe the nature of dark matter interactions. We consider a dark matter candidate that is a Standard Model singlet Dirac fermion, charged under a $U(1)_{L_\mu-L_\tau}$ symmetry. Such dark matter interacts with quarks and electrons only via loop-induced couplings, and hence is weakly constrained by direct-detection experiments and cosmic-microwave background observations. However, tree-level interactions with muons enable the dark matter to interact efficiently with the relativistic muon component of a neutron star, heating the star substantially. Using a fully relativistic approach for dark matter capture in the star, we show that observations of old cold neutron stars can probe a substantial, yet unexplored, region of parameter space for dark matter masses in the range 100 MeV - 100 GeV.