Cosmic constraints rule out s-wave annihilation of light dark matter

Understand

Light dark matter annihilating into electron-positron pairs emits a significant amount of internal bremsstrahlung that may contribute to the cosmic gamma-ray background.

• The amount of emitted gamma-rays depends on the dark matter clumping factor.
• Recent calculations indicate that this value should be of order $10^6-10^7$.
• That allows us to calculate the expected gamma-ray background contribution from dark matter annihilation.