Viewing Lepton Mixing through the Cabibbo Haze

Abstract

We explore the hypothesis that the Cabibbo angle is an expansion parameter for lepton as well as quark mixing. Cabibbo effects are deviations from zero mixing for the quarks but are deviations from unknown mixings for the leptons, such that lepton mixing is veiled by a Cabibbo haze. We present a systematic classification of parametrizations and catalog the leading order Cabibbo effects. We find that the size of the CHOOZ angle is not always correlated with the observability of CP violation. This phenomenological approach has practical merit both as a method for organizing top-down flavor models and as a guideline for planning future experiments.