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

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- and co-annihilation rates necessary to lift these dark matter-nucleon scattering bounds. For Yukawa-coupled dark matter that fits dwarf galaxy halo profiles with a coupling $\alpha ={10}^{-1}-{10}^{-4}$, a scalar mediator mass $m_\phi = 1-500$MeV,andDMmass$m_X = 0.1-10^7$ GeV, we show that fermion dark matter is unconstrained if it self-annihilates at a rate greater than $10^{-40} ~ \rm{cm^3/s}$orco-annihilateswithbaryonsatarategreaterthan$10^{-50} ~ \rm{cm^3/s}$.