Searching for velocity-dependent dark matter annihilation signals from extragalactic halos

TL;DR

This paper investigates gamma-ray signals from dark matter annihilation in extragalactic halos, focusing on velocity-dependent scenarios like p-wave and d-wave annihilation, and assesses detection prospects with current and future gamma-ray data.

Contribution

It introduces a method to analyze gamma-ray signals from extragalactic halos considering velocity-dependent dark matter annihilation, highlighting detection potential and discrimination capabilities.

Findings

Current Fermi data can hint at dark matter signals in extragalactic halos.

Larger exposure improves the ability to distinguish between p-wave and d-wave annihilation.

Extragalactic halos offer enhanced signals for velocity-dependent dark matter models.

Abstract

We consider gamma-ray signals of dark matter annihilation in extragalactic halos in the case where dark matter annihilates from a $p$-wave or $d$-wave state. In these scenarios, signals from extragalactic halos are enhanced relative to other targets, such as the Galactic Center or dwarf spheroidal galaxies, because the typical relative speed of the dark matter is larger in extragalactic halos. We perform a mock data analysis of gamma rays produced by dark matter annihilation in halos detected by the Sloan Digital Sky Survey. We include a model for uncorrelated galactic and extragalactic gamma ray backgrounds, as well as a simple model for backgrounds due to astrophysical processes in the extragalactic halos detected by the survey. We find that, for models which are still allowed by other gamma ray searches, searches of extragalactic halos with the current Fermi exposure can produce evidence for dark matter annihilation, though it is difficult to distinguish the $p$-wave and $d$-wave scenarios. With a factor $10\times$ larger exposure, though, discrimination of the velocity-dependence is possible.