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

TL;DR

This paper explores whether a fourth-generation heavy Majorana neutrino can explain cosmic ray electron and positron excesses observed by PAMELA and Fermi-LAT, analyzing decay spectra and comparing predictions with experimental data.

Contribution

It provides an analytical study of the decay spectra of a heavy Majorana neutrino and compares model predictions with cosmic ray data using novel sum rules methods.

Findings

Decay modes involving tau and muon leptons fit the lepton excess data.

Model predictions align with observed electron and positron excesses.

Tension exists between the model and antiproton-to-proton ratio constraints.

Abstract

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.