Dark matter models for the 511 keV galactic line predict keV electron recoils on Earth

TL;DR

This paper introduces dark matter models explaining the 511 keV galactic line and predicts keV electron recoils on Earth, which could account for recent XENON1T excess and are testable by multiple experiments.

Contribution

It presents novel dark matter models that explain galactic gamma-ray signals and predict detectable keV electron recoils, linking astrophysical observations with terrestrial experiments.

Findings

Models explain 511 keV galactic line via dark matter

Predict keV electron recoils detectable on Earth

Models are testable by current and future experiments

Abstract

We propose models of Dark Matter that account for the 511 keV photon emission from the Galactic Centre, compatibly with experimental constraints and theoretical consistency, and where the relic abundance is achieved via p-wave annihilations or, in inelastic models, via co-annihilations. Due to the Dark Matter component that is inevitably upscattered by the Sun, these models generically predict keV electron recoils at detectors on Earth, and could naturally explain the excess recently reported by the XENON1T collaboration. The very small number of free parameters make these ideas testable by detectors like XENONnT and Panda-X, by accelerators like NA64 and LDMX, and by cosmological surveys like the Simons observatory and CMB-S4. As a byproduct of our study, we recast NA64 limits on invisibly decaying dark photons to other particles.