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 4.6 TeV, 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 1.5 TeV μ^± events with subsequent decays into e^± plus neutrinos. For explaining this new excess together with the peak excess around 1.4 TeV, 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_μ + 1/6 N_τ) = 1 : y, with y ≃ 2.6- 10.8. For lepton portal DM models, this puts nontrivial constraint on the lepton-DM-mediator couplings λ_e : (^{λ_μ 4} + 1/6 λ_τ⁴)^1/4 = 1 :^{y 1/4} with a narrow range ^{y 1/4} ≃ 1.3- 1.8.