Sommerfeld enhancements with vector, scalar and pseudoscalar force-carriers

Understand

The first AMS-02 measurement confirms the existence of an excess in the cosmic-ray positron fraction previously reported by the PAMELA and Fermi-LAT experiments.

• If interpreted in terms of thermal dark matter (DM) annihilation, the AMS-02 result still suggests that the DM annihilation cross section in the present day should be significantly larger than that at freeze out.
• The Sommerfeld enhancement of DM annihilation cross section as a possible explanation for the observed excesses is subject to constraint from the DM thermal relic density, mainly due to the annihilation of DM particles into force-carrier particles introduced by the mechanism.
• We show that the effect of the Sommerfeld enhancement and the relic density constraint depend significantly on the nature of the force-carrier.