Flavor-dependent $U(1)$ extension inspired by lepton, baryon and color numbers

TL;DR

This paper proposes a flavor-dependent $U(1)$ gauge symmetry extension of the standard model, which explains fermion family numbers and offers solutions for neutrino mass and dark matter, with implications for flavor physics and collider experiments.

Contribution

It introduces a novel flavor-dependent $U(1)$ extension based on baryon and lepton numbers, explaining fermion family numbers and addressing neutrino mass and dark matter.

Findings

New $U(1)$ models with flavor-dependent charges

Implications for flavor-changing neutral currents

Predictions for collider phenomenology

Abstract

There is no reason why the gauge symmetry extension is family universal as in the standard model and the most well-motivated models, e.g. left-right symmetry and grand unification. Hence, we propose a simplest extension of the standard model -- a flavor-dependent $U(1)$ gauge symmetry -- and find the new physics insight. For this aim, the $U(1)$ charge, called $X$, is expressed as $X=x B+y L$ in which $x$ and $y$ are free parameters as functions of flavor index, e.g. for a flavor $i$ they take $x_i$ and $y_i$ respectively, where $B$ and $L$ denote normal baryon and lepton numbers. Imposing a relation involved by the color number $3$, i.e. $-x_{1,2,\cdots,n}=x_{n+1,n+2,\cdots,n+m}=3y_{1,2,\cdots,n+m}\equiv 3z$, for arbitrarily nonzero $z$, we achieve a novel $U(1)$ theory with implied $X$-charge. This theory not only explains the origin of the number of observed fermion families but also offers a possible solution for both neutrino mass and dark matter, which differs from $B-L$ extension. Two typical models based on this idea are examined, yielding interesting results for flavor-changing neutral currents and particle colliders, besides those of neutrino mass and dark matter.