Abstract:
We consider a concise dark matter (DM) scenario in the context of a nonexotic U(1) extension of the Standard Model (SM), where a new U(1)_x gauge symmetry is introduced along with three generations of right-handed neutrinos (RHNs) and a SM gauge singlet Higgs field. The model is a generalization of the minimal gauged U(1)_B−L (baryon number minus lepton number) extension of the SM, in which the extra U(1)_x gauge symmetry is expressed as a linear combination of the SM U(1)_y and U(1)_B−L gauge symmetries. We introduce a Z_2-parity and assign an odd-parity only for one RHN among all particles, so that this Z_2-odd RHN plays the role of DM. The so-called minimal seesaw mechanism is implemented in this model with only two Z_2-even RHNs. In this context, we investigate the physics of RHN DM, focusing on the case where this DM particle communicates with the SM particles through the U(1)_x gauge boson (Z′ boson). This “Z′-portal RHN DM” scenario is controlled by only three free parameters: the U(1)_x gauge coupling (α_x), the Z′ boson mass (m_z_′), and the U(1)_x charge of the SM Higgs doublet (x_H). We consider various phenomenological constraints to identify a phenomenologically viable parameter space. The most important constraints are the observed DM relic abundance and the latest LHC Run-2 results on the search for a narrow resonance with the dilepton final state. We find that these are complementary with each other and narrow the allowed parameter region, leading to the lower mass bound of m_z_′≳2.7 TeV.
