Universal Two-body Physics in Dark Matter near an S-wave Resonance

Understand

The dark matter annihilation rate at small relative velocities can be amplified by a large boost factor using various mechanisms, including Sommerfeld enhancement, resonance enhancement, and Breit-Wigner enhancement.

• These mechanisms all involve a resonance near the threshold for a pair of dark matter particles.
• We point out that if the resonance is in the S-wave channel, the mechanisms are equivalent sufficiently near the resonance and they are constrained by universal two-body physics.
• The amplified annihilation rate requires a corresponding amplification of the elastic scattering cross section.