Constraining the Z′ mass in 331 models using direct dark matter detection

We investigate a so-called 331 extension of the Standard Model gauge sector which accommodates neutrino masses and where the lightest of the new neutral fermions in the theory is a viable particle dark matter candidate. In this model, processes mediated by the additional Z′ gauge boson set both the dark matter relic abundance and the scattering cross section off of nuclei. We calculate with unprecedented accuracy the dark matter relic density, including the important effect of coannihilation across the heavy fermion sector, and show that indeed the candidate particle has the potential of having the observed dark matter density. We find that the recent LUX results put very stringent bounds on the mass of the extra gauge boson, MZ′≳2 TeV, independently of the dark matter mass. We also comment on the regime where our bounds on the Z′ mass may apply to generic 331-like models, and on implications for LHC phenomenology