The effect of quark interactions on dark matter kinetic decoupling and the mass of the smallest dark halos

The kinetic decoupling of dark matter (DM) from the primordial plasma sets the size of the first and smallest DM halos. Studies of the DM kinetic decoupling have hitherto mostly neglected interactions between the DM and the quarks in the plasma. Here we illustrate their importance using two frameworks: a version of the minimal supersymmetric standard model and an effective field theory with effective DM-quark interaction operators. We connect particle physics and astrophysics obtaining bounds on the smallest DM halo size from collider data and from direct DM search experiments. In the Minimal Supersymmetric Standard Model framework, adding DM-quark interactions to DM-lepton interactions more than doubles the smallest DM halo mass in a wide range of the supersymmetric parameter space.