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.
