Explain DAMPE Results by Dark Matter With Hierarchical Lepton-Specific
  Yukawa Interactions
  We propose to interpret the DAMPE electron excess at 1.5 TeV through scalar
or Dirac fermion dark matter (DM) annihilation with doubly charged scalar
mediators that have lepton-specific Yukawa couplings. Hierarchy of such
lepton-specific Yukawa couplings is generated through the Froggatt-Nielsen
mechanism, so that the dark matter annihilation products can be dominantly
electrons. Stringent constraints from LEP2 on intermediate vector boson
production can be evaded in our scenarios. In the case of scalar DM, we discuss
one scenario with DM annihilating directly to leptons and the other scenario
with DM annihilating to scalar mediators followed by their decays. We also
discuss the Breit-Wigner resonant enhancement and the Sommerfeld enhancement in
case that the s-wave annihilation process is small or helicity suppressed. With
both types of enhancement, constraints on the parameters can be relaxed and new
ways for model building will be open in explaining the DAMPE results.
