Effects of P-wave Annihilation on the Angular Power Spectrum of Extragalactic Gamma-rays from Dark Matter Annihilation

TL;DR

This paper develops a formalism to estimate the angular power spectrum of extragalactic gamma-rays from dark matter annihilation with velocity-dependent cross sections, highlighting the impact of p-wave annihilation on observable signals.

Contribution

It introduces a new formalism for modeling gamma-ray angular power spectra considering velocity-dependent dark matter annihilation, specifically applying it to p-wave scenarios.

Findings

P-wave annihilation can significantly enhance gamma-ray power if b/a >> 10^6.

The effect of p-wave annihilation on the spectrum is similar across different particle physics models.

Strong p-wave suppression makes thermal relic gamma-ray signals difficult to detect.

Abstract

We present a formalism for estimating the angular power spectrum of extragalactic gamma-rays produced by dark matter annihilating with any general velocity-dependent cross section. The relevant density and velocity distribution of dark matter is modeled as an ensemble of smooth, universal, rigid, disjoint, spherical halos with distribution and universal properties constrained by simulation data. We apply this formalism to theories of dark matter with p-wave annihilation, for which the relative-velocity-weighted annihilation cross section is \sigma v=a+bv^2. We determine that this significantly increases the gamma-ray power if b/a >> 10^6. The effect of p-wave annihilation on the angular power spectrum is very similar for the sample of particle physics models we explored, suggesting that the important effect for a given b/a is largely determined by the cosmic dark matter distribution. If the dark matter relic from strong p-wave theories is thermally produced, the intensities of annihilation gamma-rays are strongly p-wave suppressed, making them difficult to observe. If an angular power spectrum consistent with a strong p-wave were to be observed, it would likely indicate non-thermal production of dark matter in the early Universe.