Cosmic Ray Electron and Positron Excesses from a Fourth Generation Heavy Majorana Neutrino

Preprint number: CP3-Origins-2011-15 and DIAS-2011-1
Authors: Isabella Masina (University of Ferrara & CP³-Origins) and Francesco Sannino (CP3-Origins)
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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 astonishingly well the PAMELA and Fermi-LAT excesses.