  Dark matter particles will be captured in neutron stars if they undergo
scattering interactions with nucleons or leptons. These collisions transfer the
dark matter kinetic energy to the star, resulting in appreciable heating that
is potentially observable by forthcoming infrared telescopes. While previous
work considered scattering only on nucleons, neutron stars contain small
abundances of other particle species, including electrons and muons. We perform
a detailed analysis of the neutron star kinetic heating constraints on
leptophilic dark matter. We also estimate the size of loop induced couplings to
quarks, arising from the exchange of photons and Z bosons. Despite having
relatively small lepton abundances, we find that an observation of an old,
cold, neutron star would provide very strong limits on dark matter interactions
with leptons, with the greatest reach arising from scattering off muons. The
projected sensitivity is orders of magnitude more powerful than current dark
matter-electron scattering bounds from terrestrial direct detection
experiments.
