Reviving MeV-GeV Indirect Detection with Inelastic Dark Matter

Abstract

Thermal relic dark matter below $\sim 10\text{GeV}$ is excluded by cosmic microwave background data if its annihilation to visible particles is unsuppressed near the epoch of recombination. Usual model-building measures to avoid this bound involve kinematically suppressing the annihilation rate in the low-velocity limit, thereby yielding dim prospects for indirect detection signatures at late times. In this work, we investigate a class of cosmologically-viable sub-GeV thermal relics with late-time annihilation rates that are detectable with existing and proposed telescopes across a wide range of parameter space. We study a representative model of inelastic dark matter featuring a stable state ${\chi }_1$ and a slightly heavier excited state ${\chi }_2$ whose abundance is thermally depleted before recombination. Since the kinetic energy of dark matter in the Milky Way is much larger than it is during recombination, ${\chi }_1{\chi }_1\to {\chi }_2{\chi }_2$ upscattering can efficiently regenerate a cosmologically long-lived Galactic population of ${\chi }_2$, whose subsequent coannihilations with ${\chi }_1$ give rise to observable gamma-rays in the $\sim 1\text{MeV}-100\text{MeV}$ energy range. We find that proposed MeV gamma-ray telescopes, such as e-ASTROGAM, AMEGO, and MAST, would be sensitive to much of the thermal relic parameter space in this class of models and thereby enable both discovery and model discrimination in the event of a signal at accelerator or direct detection experiments.

16 pages, 8 figures

References in corpus (11)

• A Theory of Dark Matter
• Precise Relic WIMP Abundance and its Impact on Searches for Dark Matter Annihilation
• Exciting Dark Matter and the INTEGRAL/SPI 511 keV signal
• Simplified Dark Matter Models for the Galactic Center Gamma-Ray Excess
• Direct Detection of Multi-component Secluded WIMPs
• The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) Mission Concept
• Impact of Resonance on Thermal Targets for Invisible Dark Photon Searches
• Massive Argon Space Telescope (MAST): a concept of heavy time projection chamber for gamma-ray astronomy in the 100 MeV --- 1 TeV energy range
• COSI: From Calibrations and Observations to All-sky Images
• Dark Sector first results at Belle II
• A Snowmass Whitepaper: Dark Matter Production at Intensity-Frontier Experiments