Frugal U(1)X models with non-minimal flavor violation for b → sℓℓ anomalies and neutrino mixing

Abstract

We analyze the class of models with an extra U(1)X gauge symmetry that can account for the b → sℓℓ anomalies by modifying the Wilson coefficients C9e and C9μ of the operators {O}_{9mathrm{ell}}equiv left(overline{b}{gamma}_{mu }{P}_Lsright)left(overline{mathrm{ell}}{gamma}^{mu}mathrm{ell}right) from their standard model values. At the same time, these models generate appropriate quark mixing, and give rise to neutrino mixing via the Type-I seesaw mechanism. Apart from the gauge boson Z′, these frugal models only have three right-handed neutrinos for the seesaw mechanism, an additional SU(2)L scalar doublet for quark mixing, and a SM-singlet scalar that breaks the U(1)X symmetry. This set-up identifies a class of leptonic symmetries, and necessitates non-zero but equal charges for the first two quark generations. If the quark mixing beyond the standard model were CKM-like, all these symmetries would be ruled out by the latest flavor constraints on Wilson coefficients and collider constraints on Z′ parameters. However, we identify a single-parameter source of non-minimal flavor violation that allows a wider class of U(1)X symmetries to be compatible with all data. We show that the viable leptonic symmetries have to be of the form Le± 3Lμ− Lτ or Le− 3Lμ + Lτ, and determine the (MZ′, gZ′) parameter space that may be probed by the high-luminosity data at the LHC.