Sommerfeld enhancement from Goldstone pseudo-scalar exchange

Understand

We point out that the exchange of a Goldstone pseudo-scalar can provide an enhancement in the dark matter annihilation rate capable of explaining the excess flux seen in high energy cosmic ray data.

• The mechanism of enhancement involves the coupling of s and d waves through the tensor force that is very strong and, in fact, singular at short distances.
• The results indicate that large enhancements require some amount of fine tuning.
• We also discuss the enhancement due to other singular attractive potentials, such as WIMP models with a permanent electric dipole.