Masses of dark matter and neutrino from TeV-scale spontaneousU(1)B−Lbreaking

Abstract

We propose a simple testable model with mass generation mechanisms for dark matter and neutrino based on the gauged $U(1)_{B-L}$ symmetry and an exact $Z_2$ parity. The $U(1)_{B-L}$ symmetry is spontaneously broken at the TeV scale, by which $Z_2$-odd right-handed neutrinos receive Majorana masses of the electroweak scale. The lightest one is a dark matter candidate, whose stability is guaranteed by the $Z_2$ parity. Resulting lepton number violation is transmitted to the left-handed neutrinos $\nu_L^i$ via the loop-induced dimension-six operator. Consequently, the tiny masses of $\nu_L^i$ can be generated without excessive fine tuning. The observed dark matter abundance can be reproduced by the pair annihilation via the s-channel scalar exchange due to mixing of neutral components of $\Phi$ and $S$, where $\Phi$ and $S$ respectively represent the Higgs doublet and the additional scalar singlet with the $B-L$ charge. The model can be tested at collider experiments as well as flavor experiments through the discriminative predictions such as two light neutral Higgs bosons with large mixing, invisible decays of the Higgs bosons as well as the $B-L$ gauge boson, and lepton flavor violation.