  The size of the smallest dark matter collapsed structures, or protohalos, is
set by the temperature at which dark matter particles fall out of kinetic
equilibrium. The process of kinetic decoupling involves elastic scattering of
dark matter off of Standard Model particles in the early universe, and the
relevant cross section is thus closely related to the cross section for dark
matter scattering off of nuclei (direct detection) but also, via crossing
symmetries, for dark matter pair production at colliders and for pair
annihilation. In this study, we employ an effective field theoretic approach to
calculate constraints on the kinetic decoupling temperature, and thus on the
size of the smallest protohalos, from a variety of direct, indirect and
collider probes of particle dark matter.
