Two-mediator dark matter models and cosmic electron excess

TL;DR

This paper proposes a two-mediator dark matter model explaining the DAMPE electron spectrum features, including a resonance and a break, through specific annihilation channels mediated by two gauge bosons, consistent with experimental constraints.

Contribution

The paper introduces a novel two-mediator dark matter model that accounts for the DAMPE electron excess features and incorporates nonperturbative effects to reconcile annihilation cross sections.

Findings

Model explains both the resonance and break in DAMPE data.

Constraints from HESS, Fermi, AMS, and LHC are satisfied.

Sommerfeld enhancement explains large annihilation cross sections.

Abstract

The cosmic electron energy spectrum recently observed by the DAMPE experiment exhibits two interesting features, including a break around 0.9 TeV and a sharp resonance near 1.4 TeV. In this analysis, we propose a dark matter explanation to both exotic features seen by DAMPE. In our model, dark matter annihilates in the galaxy via two different channels that lead to both a narrow resonance spectrum near 1.4 TeV and electron excess events over an extended energy range thus generating the break structure around TeV. The two annihilation channels are mediated by two gauge bosons that interact both with dark matter and with the standard model fermions. Dark matter annihilations through the s-channel process mediated by the heavier boson produce monoenergetic electron-positron pairs leading to the resonance excess. The lighter boson has a mass smaller than the dark matter such that they can be on-shell produced in dark matter annihilations in the galaxy; the lighter bosons in the final state subsequently decay to generate the extended excess events due to the smeared electron energy spectrum in this process. We further analyze constraints from various experiments, including HESS, Fermi, AMS, and LHC, to the parameter space of the model where both excess events can be accounted for. In order to interpret the two new features in the DAMPE data, dark matter annihilation cross sections in the current galaxy are typically much larger than the canonical thermal cross section needed for the correct dark matter relic abundance. This discrepancy, however, is remedied by the nonperturbative Sommerfeld enhancement because of the existence of a lighter mediator in the model.