Leptobaryons as Majorana Dark Matter

We explore the dark matter and collider phenomenology of the minimal gauged $U(1{)}_B$ model, consisting of a leptophobic $Z_B$ gauge boson, and an accompanying Higgs $S_B$. By requirement of anomaly cancellation, the fermion sector naturally contains a dark matter candidate—a Majorana isosinglet $\chi$ stabilized by an inherent $Z_2$ symmetry. The absence of evidence for $Z$ prime dijet resonances at the LHC suggests that the scale of symmetry breaking ${\mathrm{\Lambda }}_B\gtrsim 500$ GeV. Saturation of dark matter abundance together with limits on the direct detection cross section (dominated by Higgs exchange) constrains the Higgs mixing angle to $\mathrm{\mid }\theta \mathrm{\mid }\lesssim 0.22$. For small mixing angles of $\mathrm{\mid }\theta \mathrm{\mid }\lesssim {10}^{-3}$, the $\mathcal{O}(10\mathrm{\%})$ branching fractions of the fermion loop-mediated $S_B\to \gamma \gamma$, $Z\gamma$, $ZZ$ modes may provide clues about the fermion content of the model at the LHC.