Testing the type II radiative seesaw model: From dark matter detection to LHC signatures

We analyze the testability of the type II radiative seesaw in which neutrino mass and dark matter (DM) are related at one-loop level. Under the constraints from DM relic density, direct and indirect detection, and invisible Higgs decays, we find three possible regions of DM mass $M_{s_1}$ that can survive the present and even the future experiments: (1) the Higgs resonance region with $M_{s_1}\sim M_h/2$, (2) the Higgs region with $M_{s_1}\sim M_h$, and (3) the coannihilation region with $M_{s_2}\sim M_{s_1}$. Here $s_{1,2}$ are two scalar singlets with the lighter $s_1$ being the DM candidate. Based on DM properties and direct collider constraints, we choose three benchmark points to illustrate the testability of this model at the LHC. We perform a detailed simulation of the four-lepton and trilepton signatures at 13(14) TeV LHC. While both signatures are found to be promising at all benchmark points, the trilepton one is even better: it is possible to reach the $5\sigma$ significance with an integrated luminosity of $100{\mathrm{fb}}^{-1}$.

Figure 1

Feynman graph for radiative neutrino mass.

Figure 2

Exclusion regions in the $M_{s_1}–M_{\chi }$ plane by ATLAS and CMS. The benchmark points in Table 2 are also indicated.

Figure 3

Scanned results shown for ${\sigma }^{\mathrm{SI}}$. The cyan, green, red, and blue lines correspond to LUX2015 [59], PandaX-II [65], LUX2016 [60], and XENON1T [56] limits, respectively. The purple points are excluded by Fermi-LAT [61]. The predictions at the three benchmark points in Table 2 are also indicated.

Figure 4

Scanned results shown in the plane of ${\lambda }_{11}^{s\mathrm{\Phi }}–M_{s_1}$ (a), ${\lambda }_{12}^{s\mathrm{\Phi }}–M_{s_1}$ (b), and $M_{s_2}–M_{s_1}$ (c). The red and blue points are excluded successively by LUX2016 [60] and XENON1T [56], and the purple points excluded by Fermi-LAT [61], while the orange points are still allowed.

Figure 5

Scanned results shown for velocity-averaged annihilation cross section times velocity $⟨\sigma v⟩$ into $b\overline{b}$ (a), $\gamma \gamma$ (b), $W^{+}{W}^{-}$ (c), and $hh$ (d), using the same legends as in Fig. 4. The dashed curves are upper bounds from Fermi-LAT [61, 62], HESS [63], and CTA [66]. The bound on $⟨\sigma v{⟩}_{hh}$ is estimated by assuming a similar $\gamma$-spectrum in the $hh$ channel as in the $W^{+}{W}^{-}$ channel [67].

Figure 6

Distributions of ${\mathrm{BR}}_{\mathrm{inv}}$ (a) and ${\lambda }_{11}^{s\mathrm{\Phi }}$ (b) as a function of $M_{s_1}$ in the low mass region, using the same legends as in Fig. 4. The dashed lines are current and expected upper bounds from the LHC.

Figure 7

Cross sections for pair and associated production of scalar triplet $\xi$ with a degenerate mass at the LHC.

Figure 8

Branching ratios of scalar triplet particles versus $M_{\xi }$ assuming $u=0.5\mathrm{GeV}$, $M_{\chi }=300\mathrm{GeV}$, and $z^{L,R}=1$.

Figure 9

Distributions of $p_T^{\ell }$, $p_T^{{\ell }_1}$, and $\eta (\ell )$ at the 13 TeV LHC for the four-lepton signature.

Figure 10

Distributions of events in $M_{{\ell }^{+}{\ell }^{-}}$, ${\cancel{E}}_T$, and $\mathrm{\Delta }{R}_{{\ell }^{\pm }{\ell }^{\pm }}$ at the 13 TeV LHC for the trilepton signature.