The 130 GeV Fingerprint of Right-Handed Neutrino Dark Matter

Abstract

Recently, an interesting indication for a dark matter signal in the form of a narrow line, or maybe two lines and/or an internal bremsstrahlung feature, has been found in data from the Fermi-LAT satellite detector. As recent analyses have also shown that there is little sign of extra contributions to continuum photons, it is natural to investigate leptophilic interacting massive particle (LIMP) models. We show that a model of radiatively generated neutrino masses may have the properties needed to explain the Fermi-LAT structure around 130 GeV. This model was proposed some 10 years ago, and predicted a clearly observable $γ$-ray signal in the Fermi-LAT (then GLAST) detector. Here, we update and improve that analysis, and show as an example that a right-handed neutrino of mass 135 GeV should give rise to three conspicuous effects: a broad internal bremsstrahlung bump with maximum around 120 GeV, a 2$γ$ line around 135 GeV, and a $Zγ$ line at 119.6 GeV (neglected in the previous work). These features together give a good fit to the 130 GeV structure, given the present energy resolution of the Fermi-LAT data. An attractive feature of the model is that the particle physics properties are essentially fixed, when relic density and mass of the right-handed neutrino dark matter particle have been set. Puzzling features of the data at present are a slight displacement of the signal from the galactic center, and a needed boost factor of order 5-15. This presents a challenge for numerical simulations including both baryons and dark matter on scales of 100 pc, and perhaps a need to go beyond the simplest halo models. With upcoming data, the double-peak structure with the two lines and the internal bremsstrahlung feature should be seen, if this model is correct. With the satellite GAMMA-400, a striking fingerprint of this dark matter candidate should then appear.