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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 $χ$ 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 $Λ_{B}\gtrsim 500$ 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 $|θ|\lesssim 0.22$. For small mixing angles of $|θ| \lesssim 10^{-3}$, the $\mathcal{O}(10\%)$ branching fractions of the fermion loop-mediated $S_B\rightarrowγγ$, $Zγ$, $ZZ$ modes may provide clues about the fermion content of the model at the LHC.