Loop-induced masses for the first two generations with optimum flavour violation

Abstract

A mechanism for the masses of third, second, and first generation charged fermions at the tree, 1-loop, and 2-loop levels, respectively, is proposed. The fermionic self-energy corrections that lead to this arrangement are induced through heavy vector bosons of a new gauged flavour symmetry group GF. It is shown that a single Abelian group suffices as GF. Moreover, the gauge charges are optimized to result in relatively smaller flavour violations in processes involving the first and second generation fermions. The scheme is explicitly implemented on the Standard Model fermions in an anomaly-free manner and is shown to be viable with observed charged fermion masses and quark mixings. Constraints from flavour violations dictate the lower limit on the new physics scale in these types of frameworks. Through optimal flavour violation, it is shown that nearly two orders of magnitude improvement can be achieved on the lower limit, leading to the new physics scale ≥ 103 TeV in this case. Further improvements are possible at the cost of the down quark mass deviating more than 3σ from its value extracted from lattice calculations. Options for inducing tiny masses for light neutrinos are also discussed.