Strong CMB Constraint On P-Wave Annihilating Dark Matter

TL;DR

This paper demonstrates that P-wave annihilating dark matter models, previously thought unconstrained by CMB anisotropy, are actually limited by CMB constraints due to bound state formation via S-wave processes.

Contribution

It reveals that bound state formation enables S-wave annihilation in P-wave dominated models, leading to new CMB constraints on dark matter parameter space.

Findings

CMB anisotropy constrains P-wave annihilating dark matter models.

Bound state formation occurs through S-wave, affecting indirect detection signals.

The parameter space of the model is limited by these new constraints.

Abstract

We consider a dark sector consisting of dark matter that is a Dirac fermion and a scalar mediator. This model has been extensively studied in the past. If the scalar couples to the dark matter in a parity conserving manner then dark matter annihilation to two mediators is dominated by the P-wave channel and hence is suppressed at very low momentum. The indirect detection constraint from the anisotropy of the Cosmic Microwave Background is usually thought to be absent in the model because of this suppression. In this letter we show that dark matter annihilation to bound states occurs through the S-wave and hence there is a constraint on the parameter space of the model from the Cosmic Microwave Background.