Minimal Flavor Protection for TeV-scale New Physics

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.

Comments: 16 pages, 2 figures, 7 tables. v2: Proof of the minimal protecting symmetry fully formalized. CP assumptions and charge-independent sector clarified