Heating up neutron stars with inelastic dark matter

Abstract

Neutron stars can provide new insight into dark matter properties, as these\ndense objects capture dark matter particles very efficiently. It has recently\nbeen shown that the energy transfer in the dark matter capture process can lead\nto appreciable heating of neutron stars, which may be observable with\nforthcoming infra-red telescopes. We examine this heating in the context of\ninelastic dark matter, for which signals in conventional nuclear-recoil based\ndirect detection experiments are highly suppressed when the momentum transfer\nis small compared to the mass splitting between dark matter states. Neutron\nstars permit inelastic scattering for much greater mass splittings, because\ndark matter particles are accelerated to velocities close to the speed of light\nduring infall. Using an effective operator approach for fermionic DM that\nscatters inelastically, we show that the observation of a very cold neutron\nstar would lead to very stringent limits on the interaction strengths that, in\nmost cases, much stronger than any present, or future, direct detection\nexperiment on Earth. This holds both for elastic scattering and for inelastic\nscattering with mass splittings up to $\\sim 300 MeV$.\n