Neutrino masses, leptogenesis, and sterile neutrino dark matter

We analyze a scenario in which the lightest heavy neutrino $N_1$ is a dark matter candidate and the second-heaviest neutrino $N_2$ decays producing a lepton number. If $N_1$ were in thermal equilibrium, its energy density today would be much larger than that of the observed dark matter, so we consider energy injection by the decay of $N_2$. In this paper, we show the parameters of this scenario that give the correct abundances of dark matter and baryonic matter and also induce the observed neutrino masses. This model can explain a possible sterile neutrino dark matter signal of $M_1=7\mathrm{keV}$ in the x-ray observation of x-ray multi-mirror mission.

Figure 1

Decay of $N_2$ by Yukawa interaction (a) and gauge interaction (b).

Figure 2

Active-sterile mixing angle of $N_1$. We plotted our result for $X_2+X_3|R_{31}{|}^2={10}^{-5}\mathrm{eV}$, ${10}^{-7}\mathrm{eV}$, and ${10}^{-9}\mathrm{eV}$. The colored region is excluded by observation (see Sec. 5). The circle at $(M_1,{\sin }^{2}2{\mathrm{\Theta }}_1)=(7\mathrm{keV},7\times 10^{-11})$ shows the possible detection reported in Refs. [22, 23].