Solving the flavour problem with hierarchical fermion wave functions

TL;DR

This paper explores a new approach to the flavor problem in particle physics, proposing that fermion mass hierarchies and flavor-changing suppression can arise from kinetic term normalizations, with implications for quark and lepton flavor transitions.

Contribution

It introduces a framework where flavor structures originate from fermion kinetic term normalizations, providing a novel solution to flavor hierarchies and FCNC suppression without extensive fine-tuning.

Findings

Quark FCNC transitions are sufficiently suppressed in this scenario.

Lepton sector faces challenges due to stringent LFV bounds.

Differences from Minimal Flavour Violation are discussed.

Abstract

We investigate the flavour structure of generic extensions of the SM where quark and lepton mass hierarchies and the suppression of flavour-changing transitions originate only by the normalization constants of the fermion kinetic terms. We show that in such scenarios the contributions to quark FCNC transitions from dimension-six effective operators are sufficiently suppressed without (or with modest) fine tuning in the effective scale of new physics. The most serious challenge to this type of scenarios appears in the lepton sector, thanks to the stringent bounds on LFV. The phenomenological consequences of this scenarios in view of improved experimental data on quark and lepton FCNC transitions, and its differences with respect to the Minimal Flavour Violation hypothesis are also discussed.