Higgs-dependent Yukawa couplings

TL;DR

The paper investigates a framework where Yukawa couplings depend on the Higgs field, so fermion masses arise from powers of the ratio $\epsilon = v^2/M^2$ with a new flavor scale $M$ in the TeV range. This leads to Higgs-fermion couplings enhanced by factors $2n_{ij}+1$, dramatically altering Higgs branching fractions and enabling Higgs-mediated flavor violation, including $h\to t\bar{c}$ and, if kinematically allowed, $t\to h c$, with typical rates around $\mathcal{O}(10^{-3})$. It also yields tree-level FCNC constrained by meson mixing and CP violation, which can be satisfied with suitably chosen textures and phases; a concrete TeV-scale UV completion with heavy vectorlike quarks demonstrates how the Yukawa structure can be generated while suppressing FCNC. The scenario predicts new TeV-scale states accessible at the LHC and distinctive Higgs phenomenology, offering a direct link between flavor dynamics and electroweak symmetry breaking and potentially contributing to electroweak baryogenesis through extra CP violation.

Abstract

We consider the possibility that the Yukawa couplings depend on the Higgs field, with the motivation of generating the fermion mass hierarchy through appropriate powers of the Higgs vacuum expectation value. This leads to drastic modifications of the Higgs branching ratios, new Higgs contributions to various flavor-violating processes, and observable rates for the top quark decay t-> hc. The underlying flavor dynamics must necessarily appear at the TeV scale and is within the reach of the LHC.

Figures (4)

• Figure 1: The various color lines show the Higgs branching ratios for different decay modes, with solid lines referring to the case of Higgs-dependent Yukawa couplings and dashed lines to the SM.
• Figure 2: The Higgs branching ratios for flavor-violating decay modes, in the case of Higgs-dependent Yukawa couplings, taking $A^{u,d}_{23} =\epsilon =m_b/m_t$ and $B^{u,d}_{23} =0$.
• Figure 3: Fermion flavor violation via Higgs line insertions. The external legs of the fermion line represent quarks of generations $i$ and $j$, while the internal propagators represent the heavy fermions $R$ and $S$.
• Figure 4: Example of a heavy quark contribution to the $K -\bar{K}$ mixing. Crosses indicate either a heavy quark mass or a Higgs VEV insertion.