Absolute neutrino mass as the missing link to the dark sector

With the KATRIN experiment, the determination of the absolute neutrino mass scale down to cosmologically favored values has come into reach. We show that this measurement provides the missing link between the Standard Model and the dark sector in scotogenic models, where the suppression of the neutrino masses is economically explained by their only indirect coupling to the Higgs field. We determine the linear relation between the electron neutrino mass and the scalar coupling ${\lambda }_5$ associated with the dark neutral scalar mass splitting to be ${\lambda }_5=3.1\times {10}^{-9}{m}_{{\nu }_e}/\mathrm{eV}$. This relation then induces correlations among the dark matter (DM) and new scalar masses and their Yukawa couplings. Together, KATRIN and future lepton flavor violation experiments can then probe the fermion DM parameter space, irrespective of the neutrino mass hierarchy and $CP$ phase.

Figure 1

Neutrino mass generation in scotogenic models.

Figure 2

Ratio of Yukawa couplings as a function of the lightest neutrino mass $m_{{\nu }_1}$ with mass difference/mixing (grey), LFV (blue), relic density (green) and all constraints (red points).

Figure 3

The dark sector-Higgs boson coupling $|{\lambda }_5|$ as a function of lightest neutrino mass $m_{{\nu }_1}$ with LFV (blue), relic density (green) and all constraints (red points).

Figure 4

Yukawa coupling of the lightest neutrino as a function of the DM mass. The ratio of the neutral scalar over the DM mass is given on the temperature scale.

Figure 5

Branching ratios of viable scotogenic models for the LFV processes $\mu \to e\gamma$ (blue) and $\mu \to 3e$ (red points), their current (full) [21, 23] and future (dashed) [22, 24] experimental limits, and the current [9] and future [10] KATRIN limits (yellow lines) on the (effective) electron neutrino mass.