3.5 keV X-ray Line Signal from Decay of Right-Handed Neutrino due to Transition Magnetic Moment

Understand

We consider the dark matter model with radiative neutrino mass generation where the Standard Model is extended with three right-handed singlet neutrinos ($N_1$, $N_2$ and $N_3$) and one additional SU(2)$_L$ doublet scalar $\eta$.

• One of the right-handed neutrinos ($N_1$), being lightest among them, is a leptophilic fermionic dark matter candidate whose stability is ensured by the imposed $\mathbb{Z}_2$ symmetry on this model.
• The second lightest right-handed neutrino ($N_2$) is assumed to be nearly degenerated with the lightest one enhancing the co-annihilation between them.
• The effective interaction term among the lightest, second lightest right-handed neutrinos and photon containing transition magnetic moment is responsible for the decay of heavier right-handed neutrino to the lightest one and a photon ($N_2\to N_1 + \gamma$).