Self-resonant Dark Matter

We present a novel mechanism for Sommerfeld enhancement for dark matter interactions without the need for light mediators. Considering a model for two-component dark matter with a triple coupling, we find that one of dark matter particles leads to an $u$-channel resonance in dark matter elastic scattering. From the sum of the $u$-channel ladder diagrams, we obtain a Bethe-Salpeter equation with a delay term and identify the Sommerfeld factor from the elastic scattering of two dark matter components for the first time. We discuss the implications of our results for enhancing dark matter self-scattering and annihilation.