From Eq. (19), one can see that σ(p)
SI ∝ (sin 2θ/v′)2 for a given DM mass mN . Fig. 3 shows
the spin-independent cross section of RH neutrino with a proton. T he resultant cross section
is found to be far below the current limits reported by XENON10 [24] and CDMSII [25]:
σSI ≲ 4 × 10−8 − 2 × 10−7 pb, for a DM mass of 100 GeV-1 TeV. Future experiments such
as XENON1T [26] can reach the cross section predicted in our model.
10 -10
10 -9
10 -8
 60  80  100  120  140  160  180  200
σ p   [pb]
m N   [GeV]
FIG. 3: The spin independent scattering cross section with aproton. All parameters are same as
those used in the previous section. The upper and lower linescorrespond to sinθ = 0. 7 and 0. 3,
respectively.
IV. SUMMARY
We have proposed a scenario of the RH neutrino dark matter in the c ontext of the minimal
gauged U(1)B−L model. We have introduced a discrete Z2 parity in the model, so that one
RH neutrino assigned as Z2-odd can be stable and, hence, the DM candidate, while the other
two RH neutrinos account for neutrino masses and mixings through the seesaw mechanism.
No additional degrees of freedom are necessary to be added. We h ave evaluated the relic
density of the dark matter particle. The dominant annihilation modes are via the Higgs
boson exchange processes in the s-channel and thus, our model can be called Higgs portal
DM model. It has been found that the relic density consistent with th e current observation
8