Minimal Flavor Protection for TeV-scale New Physics

TL;DR

This paper identifies the minimal flavor symmetry subgroup that allows TeV-scale new physics to deviate from flavor universality while respecting experimental bounds, offering a new approach to flavor protection in particle physics.

Contribution

It introduces the $SU(2)_q imes U(1)_X$ symmetry as the minimal flavor protection subgroup compatible with TeV-scale new physics and observed fermion hierarchies.

Findings

Reproduces fermion hierarchies with small symmetry-breaking spurions.

Provides structural flavor protection within SMEFT for TeV-scale physics.

Expands the viable flavor violation scenarios beyond MFV and $U(2)^5$.

Abstract

We determine how much TeV-scale new physics can deviate from flavor universality, $U(3)^5$, while respecting stringent bounds on flavor-changing neutral currents. The minimal continuous subgroup that must be approximately preserved is identified as $SU(2)_{q} \times U(1)_{X}$. With only a few symmetry-breaking spurions of $\mathcal{O}(10^{-2})$, all observed fermion hierarchies may be reproduced, offering a new perspective on the SM flavor puzzle. Remarkably, this framework provides structural flavor protection for generic TeV-scale new physics within the SMEFT, enlarging the space of collider-accessible scenarios beyond MFV and $U(2)^5$ and allowing for richer patterns of flavor violation.