Muon Anomaly and Dark Parity Violation

Abstract

The muon anomalous magnetic moment exhibits a 3.6 sigma discrepancy between experiment and theory. One explanation requires the existence of a light vector boson, Z(d) (the dark Z), with mass 10-500 MeV that couples weakly to the electromagnetic current through kinetic mixing. Support for such a solution also comes from astrophysics conjectures regarding the utility of a U(1)(d) gauge symmetry in the dark matter sector. In that scenario, we show that mass mixing between the Z(d) and ordinary Z boson introduces a new source of "dark'' parity violation, which is potentially observable in atomic and polarized electron scattering experiments. Restrictive bounds on the mixing (m(Zd)/m(Z))delta are found from existing atomic parity violation results, delta(2) < 2 x 10(-5). Combined with future planned and proposed polarized electron scattering experiments, a sensitivity of delta(2) x 10(-6) is expected to be reached, thereby complementing direct searches for the Z(d) boson.