Confronting the DAMPE excess with the scotogenic type-Ⅱ seesaw model

The DArk Matter Particle Explorer（DAMPE） has observed a tentative peak at E ～1.4 Te V in the cosmic-ray electron spectrum.In this paper,we interpret this excess in the scotogenic type-Ⅱ seesaw model.This model extends the canonical type-Ⅱ seesaw model with dark matter（DM） candidates and a loop-induced vacuum expectation value of the triplet scalars,v△,resulting in small neutrino masses naturally even for Te V scale triplet scalars.Assuming a nearby DM subhalo,the DAMPE excess can be explained by DM annihilating into a pair of triplet scalars which subsequently decay to charged lepton final states.Spectrum fitting of the DAMPE excess indicates it potentially favors the inverted neutrino mass hierarchy.We also discuss how to evade associated neutrino flux in our model.

Quasi-degenerate dark matter for DAMPE excess and 3.5 ke V line

We propose a quasi-degenerate dark matter scenario to simultaneously explain the 1.4 TeV peak in the high-energy cosmic-ray electron-positron spectrum reported by the DAMPE collaboration very recently and the 3.5 keV X-ray line observed in galaxies clusters and from the Galactic centre and confirmed by the Chandra and NuSTAR satellites. We consider a dark S U（2）′× U（1）′ gauge symmetry under which the dark matter is a Dirac fermion doublet composed of two S U（2）′ doublets with non-trivial U（1 ）′ charges. At the one-loop level the two dark fermion components can have a mass split as a result of the dark gauge symmetry breaking. Through the exchange of a mediator scalar doublet the two quasi-degenerate dark fermdons can mostly annihilate into the electron-positron pairs at the tree level for explaining the 1.4 TeV positron anomaly, meanwhile, the heavy dark fermion can very slowly decay into the light dark fermion with a photon at the one-loop level for explaining the 3.5 keV X-ray line. Our dark fermions can be also verified in the direct detection experiments.