Muon g-2, rare kaon decays, and parity violation from dark bosons

Abstract

The muon g(mu) - 2 discrepancy between theory and experiment may be explained by a light vector boson Z(d) that couples to the electromagnetic current via kinetic mixing with the photon. We illustrate how the existing electron g(e) - 2, pion Dalitz decay, and other direct production data disfavor that explanation if the Z(d) mainly decays into e(+)e(-), mu(+)mu(-). Implications of a dominant invisible Z(d) decay channel, such as light dark matter, along with the resulting strong bounds from the rare K -> pi + missing energy decay are examined. The K decay constraints may be relaxed if destructive interference effects due to Z - Z(d) mass mixing are included. In that scenario, we show that accommodating the g(mu) - 2 data through relaxation of K decay constraints leads to interesting signals for dark parity violation. As an illustration, we examine the alteration of the weak mixing angle running at low Q(2), which can be potentially observable in polarized electron scattering or atomic physics experiments.