Low Q² weak mixing angle measurements and rare Higgs decays.

A weighted average weak mixing angle θW derived from relatively low Q² experiments is compared with the standard model prediction obtained from precision measurements. The approximate 1.8 sigma discrepancy is fit with an intermediate mass (~10-35 GeV) "dark" Z boson Zd, corresponding to a U(l)d gauge symmetry of hidden dark matter, which couples to our world via kinetic and Z-Zd mass mixing. Constraints on such a scenario are obtained from precision electroweak bounds and searches for the rare Higgs decays H → ZZd → 4 charged leptons at the LHC. The sensitivity of future anticipated low Q² measurements of sin² θW (Q²) to intermediate mass Zd is also illustrated. This dark Z scenario can provide interesting concomitant signals in low energy parity violating measurements and rare Higgs decays at the LHC over the next few years. [ABSTRACT FROM AUTHOR]