Gauged Flavor Group with Left-Right Symmetry

TL;DR

This paper develops an anomaly-free extension of the left-right symmetric model with gauged flavor symmetry, analyzing constraints on the flavor symmetry scale and implications for neutrino masses and the strong CP problem.

Contribution

It introduces a novel anomaly-free gauged flavor symmetry in left-right models, with detailed analysis of experimental constraints and implications for neutrino masses and CP violation.

Findings

Flavor symmetry scale can be as low as a few TeV under certain conditions.

Constraints mainly come from WR-mediated flavor changing neutral currents, especially K-Kbar mixing.

The model offers a framework for neutrino masses and addresses the strong CP problem.

Abstract

We construct an anomaly-free extension of the left-right symmetric model, where the maximal flavor group is gauged and anomaly cancellation is guaranteed by adding new vectorlike fermion states. We address the question of the lowest allowed flavor symmetry scale consistent with data. Because of the mechanism recently pointed out by Grinstein et al. tree-level flavor changing neutral currents turn out to play a very weak constraining role. The same occurs, in our model, for electroweak precision observables. The main constraint turns out to come from WR-mediated flavor changing neutral current box diagrams, primarily K - Kbar mixing. In the case where discrete parity symmetry is present at the TeV scale, this constraint implies lower bounds on the mass of vectorlike fermions and flavor bosons of 5 and 10 TeV respectively. However, these limits are weakened under the condition that only SU(2)_R x U(1)_{B-L} is restored at the TeV scale, but not parity. For example, assuming the SU(2) gauge couplings in the ratio gR/gL approx 0.7 allows the above limits to go down by half for both vectorlike fermions and flavor bosons. Our model provides a framework for accommodating neutrino masses and, in the parity symmetric case, provides a solution to the strong CP problem. The bound on the lepton flavor gauging scale is somewhat stronger, because of Big Bang Nucleosynthesis constraints. We argue, however, that the applicability of these constraints depends on the mechanism at work for the generation of neutrino masses.