What if the Masses of the First Two Quark Families are not Generated by the Standard Higgs?

TL;DR

This paper explores alternative mechanisms for generating the masses of the first two quark families beyond the Standard Model Higgs, proposing new symmetries and physics that lead to distinctive Higgs couplings and flavor-changing processes.

Contribution

It introduces two novel scenarios for quark mass generation involving a new symmetry and high-energy physics, predicting enhanced Higgs couplings and flavor-violating top decays.

Findings

Suppressed flavor-changing neutral currents in both models.

Enhanced Higgs couplings to s and c quarks in the high-energy physics scenario.

Predicted top decay branching ratio Br(t→hc) ≥ 5×10^{-5}.

Abstract

We point out that, in the context of the SM, $|V^2_{13}| + | V^2_{23}|$ is expected to be large, of order one. The fact that $|V^2_{13}| + |V^2_{23}| \approx 1.6 \times 10^{-3}$ motivates the introduction of a symmetry S which leads to $V_{CKM} ={1\>\!\!\!\mathrm{I}} $, with only the third generation of quarks acquiring mass. We consider two scenarios for generating the mass of the first two quark generations and full quark mixing. One consists of the introduction of a second Higgs doublet which is neutral under S. The second scenario consists of assuming New Physics at a high energy scale , contributing to the masses of light quark generations, in an effective field theory approach. This last scenario leads to couplings of the Higgs particle to $s\overline s$ and $c \overline c$ which are significantly enhanced with respect to those of the SM. In both schemes, one has scalar-mediated flavour- changing neutral currents which are naturally suppressed. Flavour violating top decays are predicted in the second scenario at the level $ \mbox{Br} (t \rightarrow h c ) \geq 5\times 10^{-5}$.