"Dark" Z implications for parity violation, rare meson decays, and Higgs physics.

General consequences of mass mixing between the ordinary Ζ boson and a relatively light Z,d boson, the "dark" Z, arising from a U(1)d gauge symmetry, associated with a hidden sector such as dark matter, are examined. New effects beyond kinetic mixing are emphasized. Z-Zd mixing introduces a new source of low energy parity violation well explored by possible future atomic parity violation and planned polarized electron scattering experiments. Rare K(B) meson decays into π(Κ)ℓ+ℓ-(ℓ = e, μ) and π(K)vv̄ are found to already place tight constraints on the size of Z-Zd mixing. Those sensitivities can be further improved with future dedicated searches at Κ and Β factories as well as binned studies of existing data. Z-Zd mixing can also lead to the Higgs decay Η → ZZd, followed by Ζ → ℓ+1ℓ-1 and Zd → ℓ+2ℓ-2 or "missing energy," providing a potential hidden sector discovery channel at the Large Hadron Collider. An illustrative realization of these effects in a 2 Higgs doublet model is presented. [ABSTRACT FROM AUTHOR]