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- 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 $m_{\varphi }=1-500$ MeV, and DM mass $m_X=0.1-10^7$ GeV, we show that fermion dark matter is unconstrained if it self-annihilates at a rate greater than $10^{-40}\mathrm{c}{\mathrm{m}}^3/s$ or co-annihilates with baryons at a rate greater than $10^{-50}\mathrm{c}{\mathrm{m}}^3/s$.

Comments: 35 pages, 8 figures, corrected typos