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

TL;DR

This paper uses cosmic gamma-ray background measurements to constrain light dark matter models, ruling out s-wave annihilation for light dark matter but not for heavier candidates like neutralinos.

Contribution

It provides new constraints on light dark matter annihilation based on cosmic gamma-ray background data, especially ruling out s-wave annihilation.

Findings

Light dark matter s-wave annihilation is incompatible with observed gamma-ray background.

Constraints are weaker for more massive dark matter like neutralinos.

Clumping factor significantly influences gamma-ray emission estimates.

Abstract

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. We find that the light dark matter model can be ruled out if a constant thermally-averaged cross section is assumed (s-wave annihilation). For more massive dark matter candidates like neutralinos, however, cosmic constraints are weaker.