Universally enhanced light-quarks Yukawa couplings paradigm

Abstract

We propose that natural TeV-scale new physics (NP) with ${\cal O}(1)$ couplings to the standard model (SM) quarks may lead to a universal enhancement of the Yukawa couplings of all the light quarks, perhaps to a size comparable to that of the SM b-quark Yukawa coupling, i.e., $y_q \sim {\cal O}(y_b^{SM})$ for $q=u,d,c,s$. This scenario is described within an effective field theory (EFT) extension of the SM, for which a potential contribution of certain dimension six effective operators to the light quarks Yukawa couplings is $y_q \sim {\cal O} \left( f \frac{v^2}{\Lambda^2} \right)$, where $v$ is the Higgs vacuum expectation value (VEV), $v=246$ GeV, $\Lambda$ is the typical scale of the underlying heavy NP and $f$ is the corresponding Wilson coefficient which depends on its properties and details. In particular, we study the case of $y_q \sim 0.025 \sim y_b^{SM}$, which is the typical size of the enhanced light-quark Yukawa couplings if the NP scale is around $\Lambda \sim 1.5$ TeV and the NP couplings are natural, i.e., $f \sim {\cal O}(1)$. We also explore this enhanced light quarks Yukawa paradigm in extensions of the SM which contain TeV-scale vector-like quarks and we match them to the specific higher dimensional effective operators in the EFT description. We discuss the constraints on this scenario and the flavor structure of the underlying NP dynamics and suggest some resulting "smoking gun" signals that should be searched for at the LHC, such as multi-Higgs production $pp \to hh,hhh$ and single Higgs production in association with a high $p_T$ jet ($j$) or photon $pp \to hj,h \gamma$ and with a single top-quark $pp \to h t$.