Forbidden Dark Matter Annihilations into Standard Model Particles

TL;DR

This paper introduces a novel mechanism of forbidden dark matter annihilations into Standard Model leptons, which precisely determines the dark matter mass for the observed relic abundance and has testable experimental implications.

Contribution

It proposes a new class of dark matter models based on forbidden annihilations, linking dark matter mass to Standard Model lepton masses and experimental signatures.

Findings

Forbidden annihilations fix dark matter mass near lepton masses.

Next-generation experiments can probe most of the parameter space.

Model explains the muon g-2 anomaly.

Abstract

We present kinematically forbidden dark matter annihilations into Standard Model leptons. This mechanism precisely selects the dark matter mass that gives the observed relic abundance. This is qualitatively different from existing models of thermal dark matter, where fixing the relic density typically leaves open orders of magnitude of viable dark matter masses. Forbidden annihilations require the dark matter to be close in mass to the particles that dominate its annihilation rate. We show examples where the dark matter mass is close to the muon mass, the tau mass, or the average of the tau and muon masses. We find that most of the relevant parameter space can be covered by the next generation of proposed beam-dump experiments and future high-luminosity electron positron colliders. Forbidden dark matter predicts large couplings to the Standard Model that can explain the observed value of $(g-2)_\mu$.