Flavor Structure of the Cosmic-Ray Electron/Positron Excesses at DAMPE.

The Dark Matter Particle Explorer (DAMPE) satellite detector announced its first result for measuring the cosmic-ray electron/positron (CRE) energy spectrum up to 4.6TeV, including a tentative peak-like event excess at (1.3-1.5)TeV. In this work, we uncover a significant hidden excess in the DAMPE CRE spectrum over the energy range (0.6-1.1)TeV, which has a non-peak-like structure. We propose a new mechanism to explain this excess by a set of 1.5TeV $\mu^\pm$ events with subsequent decays into $e^\pm$ plus neutrinos. For explaining this new excess together with the peak excess around 1.4TeV, we demonstrate that the flavor structure of the original lepton final-state produced by dark matter (DM) annihilations (or other mechanism) should have a composition ratio $N_e : (N_\mu + \frac 1 6 N_\tau) = 1:y$, with $y \simeq 2.6-10.8$. For lepton portal DM models, this puts important constraint on the lepton-DM-mediator couplings $\lambda_e : (\lambda^4_\mu + \frac 1 6 \lambda^4_\tau)^{\frac 1 4} = 1:y^{\frac 1 4}$ with a narrow range $y^{\frac 1 4} \simeq 1.3-1.8$.