WIMPonium and Boost Factors for Indirect Dark Matter Detection

TL;DR

This paper proposes that WIMP dark matter can form bound states called WIMPonium, which significantly enhances annihilation signals and produces distinctive gamma-ray lines, improving indirect detection prospects.

Contribution

It introduces the concept of WIMPonium bound states in dark matter models, showing their potential to boost annihilation signals and produce observable gamma-ray lines.

Findings

WIMPonium can cause substantial annihilation rate enhancements.

Multiple gamma-ray lines can be produced from WIMPonium decays.

Boost factors can be large without requiring high dark matter densities.

Abstract

We argue that WIMP dark matter can annihilate via long-lived "WIMPonium" bound states in reasonable particle physics models of dark matter (DM). WIMPonium bound states can occur at or near threshold leading to substantial enhancements in the DM annihilation rate, closely related to the Sommerfeld effect. Large "boost factor" amplifications in the annihilation rate can thus occur without large density enhancements, possibly preferring colder less dense objects such as dwarf galaxies as locations for indirect DM searches. The radiative capture to and transitions among the WIMPonium states generically lead to a rich energy spectrum of annihilation products, with many distinct lines possible in the case of 2-body decays to $\gamma\gamma$ or $\gamma Z$ final states. The existence of multiple radiative capture modes further enhances the total annihilation rate, and the detection of the lines would give direct over-determined information on the nature and self-interactions of the DM particles.