Self-resonant Dark Matter

We present a review on the self-resonant dark matter scenarios where multiple components of dark matter give rise to a resonant condition in the $u$-channel diagrams for their comparable masses. In this case, there is no need of lighter mediators for enhancing the self-scattering and annihilation cross sections for dark matter. We discuss the velocity-dependent self-scattering for the small-scale problems, the relic density of self-resonant dark matter, and the observable signatures in indirect and detection experiments.