Neutrino mixing and $R_K$ anomaly in $U(1{)}_X$ models: a bottom-up approach

Abstract

We identify a class of $U(1{)}_X$ models which can explain the $R_K$ anomaly and the neutrino mixing pattern, by using a bottom-up approach. The different $X$-charges of lepton generations account for the lepton universality violation required to explain $R_K$. In addition to the three right-handed neutrinos needed for the Type-I seesaw mechanism, these minimal models only introduce an additional doublet Higgs and a singlet scalar. While the former helps in reproducing the quark mixing structure, the latter gives masses to neutrinos and the new gauge boson $Z^{\prime }$. Our bottom-up approach determines the $X$-charges of all particles using theoretical consistency and experimental constraints. We find the parameter space allowed by the constraints from neutral meson mixing, rare $b\to s$ decays and direct collider searches for $Z^{\prime }$. Such a $Z^{\prime }$ may be observable at the ongoing run of the Large Hadron Collider with a few hundred fb${}^{-1}$ of integrated luminosity.

Comments: 29 pages, 6 figures, minor typos corrected, one comment and references added, matches with the version published in JHEP