Bounds on self-interacting fermion dark matter from observations of old neutron stars

Abstract

The existence of old neutron stars deeply constrains self-interacting fermion dark matter, which can form star-killing black holes. We quantify this constraint on dark matter-nucleon scattering, considering collapse scenarios that broaden bounds over intermediate masses. We then find the self-annihilation and coannihilation rates necessary to lift these dark matter-nucleon scattering bounds. For Yukawa-coupled dark matter that fits dwarf galaxy halo profiles with a coupling $\ensuremath{\alpha}=1{0}^{\ensuremath{-}1}--1{0}^{\ensuremath{-}4}$, a scalar mediator mass ${m}_{\ensuremath{\phi}}=1--500\text{ }\text{ }\mathrm{MeV}$, and dark matter mass ${m}_{X}=0.1--1{0}^{7}\text{ }\text{ }\mathrm{GeV}$, we show that fermion dark matter is unconstrained if it self-annihilates at a rate greater than $1{0}^{\ensuremath{-}40}\text{ }\text{ }{\mathrm{cm}}^{3}/\mathrm{s}$ or coannihilates with baryons at a rate greater than $1{0}^{\ensuremath{-}50}\text{ }\text{ }{\mathrm{cm}}^{3}/\mathrm{s}$.