7 keV sterile neutrino Dark Matter in extended seesaw framework

The appearance of a $3.5$ keV photon line in the X-ray spectra of Andromeda galaxy and other galaxy clusters including the Perseus galaxy can be interpreted as the signal of a $7$ keV sterile neutrino dark matter candidate as one of the plausible explanations. We present here a novel framework of extended seesaw mechanism where the lightest sterile neutrino acts as a Dark Matter candidate and its decay into a photon and an ordinary neutrino accounts for the excess 3.5 keV X-ray line. For implementing the idea, we add two different types of neutral fermion singlets ($S_L$, $N_R$) to the SM light neutrino $\nu_L$ so that the light neutrino mass is governed by generic linear seesaw formula. We discuss the complementarity constraints on the model parameters including sterile-active neutrino mixing angle within the extended seesaw framework. Favorably, this framework can be embedded in a $SO(10)$ grand unified theory.