Cosmic Ray Electron and Positron Excesses from a Fourth Generation Heavy
  Majorana Neutrino
  Unexpected features in the energy spectra of cosmic rays electrons and
positrons have been recently observed by PAMELA and Fermi-LAT satellite
experiments, opening to the exciting possibility of an indirect manifestation
of new physics. A TeV-scale fourth lepton family is a natural extension of the
Standard Model leptonic sector (also linked to the hierarchy problem in Minimal
Walking Technicolor models). The heavy Majorana neutrino of this setup mixes
with Standard Model charged leptons through a weak charged current interaction.
Here, we first study analytically the energy spectrum of the electrons and
positrons originated in the heavy Majorana neutrino decay modes, also including
polarization effects. We then compare the prediction of this model with the
experimental data, exploiting both the standard direct method and our recently
proposed Sum Rules method. We find that the decay modes involving the tau
and/or the muon charged leptons as primary decay products fit well the PAMELA
and Fermi-LAT lepton excesses while there is tension with respect to the
antiproton to proton fraction constrained by PAMELA.
