Neutron star observations of pseudoscalar-mediated dark matter

TL;DR

This paper explores how neutron star heating can detect pseudoscalar-mediated dark matter, offering a promising alternative to traditional direct detection methods, especially for certain mass ranges and mediator models.

Contribution

It demonstrates that neutron star heating can probe pseudoscalar-mediated dark matter beyond current direct detection and collider bounds in two specific models.

Findings

Neutron star heating can detect sub-10 GeV dark matter with axion-like mediators.

Heavier dark matter (>10 GeV) mediated by pseudoscalars mixing with 2HDM can be constrained.

Upcoming neutron star observations will surpass existing bounds from flavor, beam dump, and collider experiments.

Abstract

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 v ~ 0.001 c. 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 semi-relativistic speeds. We investigate this phenomenon in the context of two specific, self-consistent 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 axion-like particle (ALP), 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+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.