Hierarchical radiative fermion masses and flavor changing processes in an $U(1)_X$ horizontal symmetry model

Abstract

In a model with a gauge group $G_{SM}\otimes U(1)_X$, where $G_{SM} \equiv SU(3)_C \otimes SU(2)_L \otimes U(1)_Y$ is the standard model gauge group and $U(1)_X$ is a horizontal local gauge symmetry, the spectrum of charged fermion masses and mixing angles are obtained from radiative contributions with the aim to reproduce the fermion masses and the Cabibbo-Kobayashi-Maskawa matrix with no {\it a priori} texture assumption. The assignment of horizontal charges is made such that at tree level only the third family becomes massive when electroweak symmetry is broken. Using these tree level masses and introducing exotic scalars, the light families of charged fermions acquire hierarchical masses through radiative corrections. The rank three mass matrices obtained are written in terms of a minimal set of free parameters in order to estimate their values by a numerical fit performance. The resulting masses and CKM mixing angles turn out to be in good agreement with the known values. The new exotic scalar fields mediate flavor changing processes and contribute to the anomalous magnetic moments of fermions, additionaly branching ratios an$ magnetic moments contributions were evaluated for leptons.