Powerful Yukawas

TL;DR

The paper explores the possibility that light SM fermion masses originate from higher-dimension Yukawa-like operators, creating a Powerful Yukawa (PY) scenario in which the Higgs-fermion coupling is enhanced for light generations. It develops a bottom-up EFT with a chain of flavor symmetries and spurions, deriving the scaling of the effective Yukawas and the requirement that new physics lie at a relatively low scale to avoid radiative, lower-dimension contamination. A concrete UV completion based on Sprouted Symmetry Breaking introduces four-Higgs-doublet sprouts that generate the PY operator at tree level, while radiative corrections reintroduce lower-dimension operators and set the scale for new states to be around the TeV range. Phenomenology is examined in SMEFT and flavor sectors, showing that while additional SMEFT effects can be suppressed, specific flavor structures (notably in leptons and quarks) face distinct experimental constraints, suggesting selective viability of PY realizations and guiding future collider and flavor probes.

Abstract

We introduce a class of models where the masses of the light Standard Model fermions are due to an Effective Field Theory operator that appears beyond dimension-4 in the power counting expansion, resulting in a `Powerful Yukawa'. The effective Yukawa coupling structure is UV-completed using a collective symmetry breaking pattern in the flavour sector, which we dub `Sprouted Symmetry Breaking.' The irreducible signature is an enhanced Higgs coupling to the light Standard Model fermions.

Figures (2)

• Figure 1: Structure of a symmetry-protected sprout. If the operators $\mathcal{O}_{i}$ only contain light fields, this leads to an EFT operator of the form in \ref{['eq:LEFT4Os']}. If any of the $\mathcal{O}_{i}$ contain heavy fields, they will be connected to further sprouts, forming a tree that leads to an even higher dimension EFT operator.
• Figure 2: One-loop diagrams that generate lower-dimension Yukawa couplings.