Triplet dark matter from leptogenesis

A triplet dark matter candidate from thermal leptogenesis is considered with building a model. The model is based on the standard two-Higgs-doublet model and seesaw mechanism with Higgs triplets. The parameters (couplings and masses) are adjusted for the observed small neutrino mass and the leptogenesis. Dark matter particles can annihilate and decay in this model. The time evolution of the dark matter number is governed by (co)annihilations in the expanding universe, and its mass is constrained by the observed relic density. The dark matter can decay into final states with three leptons (two charged leptons and one neutrino). We investigate whether the decay in a galaxy can account for cosmic ray anomalies in the positron and electron spectrum. A noticeable point is that if the dark matter decays into each lepton with different branching ratios, cosmic ray anomalies in AMS-02 measurements of the positron fraction and the Fermi LAT measurements of the electrons-plus-positrons flux could be simultaneously accounted for from its decay products.

Figure 1

The decay of ${\chi }_1^{*}⟶\ell \ell$, $\psi e$ at tree level and in one-loop order. A lepton asymmetry is generated by their interference.

Figure 2

Predicted cosmic ray signals with DM mass 2.5 TeV for branching ratios $B_e=6\%$, $B_{\mu }=6\%$, and $B_{\tau }=88\%$ and lifetime $2.0\times {10}^{26}\sec$. Left panels: Positron fraction with experimental data: AMS-02 [13], PAMELA [14, 15], and Fermi LAT [49]. Right panels: Positrons-plus-electrons flux with experimental data: PAMELA (electron only) [44], Fermi LAT [16], HESS [17, 18], PPB-BETS [50], and ATIC [51]. The bold dotted line shows the astrophysical background. Solar modulation is taken into account by using the force field approximation with the Fisk potential 600 MV.