Neutron star observations of pseudoscalar-mediated dark matter

Understand

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).