Neutron star observations of pseudoscalar-mediated dark matter

Scattering interactions between dark matter and Standard Model states mediated by pseudoscalars are generically challenging to uncover at direct detection experiments due to rates suppressed by powers of the local dark matter velocity vDM similar to 10-3c. However, they may be observed in the dark matter-induced heating of neutron stars, whose steep gravitational potentials prevent such suppression by accelerating infalling particles to semirelativistic speeds. We investigate this phenomenon in the context of two specific, selfconsistent scenarios for pseudoscalars coupled to dark matter, and compare the sensitivity of neutron star heating to bounds from direct searches for the mediators and dark matter. The first lighter scenario consists of sub-10 GeV mass dark matter mediated by an axionlike particle, while the second heavier scenario has dark matter above 10 GeV mediated by a dark pseudoscalar that mixes with a pseudoscalar from a two-Higgs doublet (the so-called 2HDM thorn a model). In both frameworks, we show that imminent measurements of neutron stars will be able to test pseudoscalar-mediated dark matter beyond the reach of direct dark matter searches as well as bounds on the mediators from flavor observables, beam dump experiments, and high-energy colliders.

Automated summary

Scattering interactions between dark matter and Standard Model states mediated by pseudoscalars are difficult to detect at direct detection experiments. However, they can be observed in the dark matter-induced heating of neutron stars. This study investigates this phenomenon and compares the sensitivity of neutron star heating to bounds from direct searches for the mediators and dark matter.