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Register a new userA universally enhanced light-quarks Yukawa couplings paradigm
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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 $pp to h t$.
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We suggest that the exclusive Higgs + light (or b)-jet production at the LHC, $pp to h+j(j_b)$, is a rather sensitive probe of the light-quarks Yukawa couplings and of other forms of new physics (NP) in the Higgs-gluon $hgg$ and quark-gluon $qqg$ interactions. We study the Higgs $p_T$-distribution in $pp to h+j(j_b) to gamma gamma + j(j_b)$, i.e., in $h+j(j_b)$ production followed by the Higgs decay $h to gamma gamma$, employing the ($p_T$-dependent) signal strength formalism to probe various types of NP which are relevant to these processes and which we parameterize either as scaled Standard Model (SM) couplings (the kappa-framework) and/or through new higher dimensional effective operators (the SMEFT framework). We find that the exclusive $h+j(j_b)$ production at the 13 TeV LHC is sensitive to various NP scenarios, with typical scales ranging from a few TeV to ${cal O}(10)$ TeV, depending on the flavor, chirality and Lorentz structure of the underlying physics.
A common lore has arisen that beyond the Standard Model (BSM) particles, which can be searched for at current and proposed experiments, should have flavorless or mostly third-generation interactions with Standard Model quarks. This theoretical bias severely limits the exploration of BSM phenomenology, and is especially constraining for extended Higgs sectors. Such limitations can be avoided in the context of Spontaneous Flavor Violation (SFV), a robust and UV complete framework that allows for significant couplings to any up or down-type quark, while suppressing flavor-changing neutral currents via flavor alignment. In this work we study the theory and phenomenology of extended SFV Higgs sectors with large couplings to any quark generation. We perform a comprehensive analysis of flavor and collider constraints of extended SFV Higgs sectors, and demonstrate that new Higgs bosons with large couplings to the light quarks may be found at the electroweak scale. In particular, we find that new Higgses as light as 100 GeV with order $sim$ 0.1 couplings to first or second generation quarks, which are copiously produced at LHC via quark fusion, are allowed by current constraints. Furthermore, the additional SFV Higgses can mix with the SM Higgs, providing strong theory motivation for an experimental program looking for deviations in the light quark-Higgs couplings. Our work demonstrates the importance of exploring BSM physics coupled preferentially to light quarks, and the need to further develop dedicated experimental techniques for the LHC and future colliders.
We show that both flavor-conserving and flavor-violating Yukawa couplings of the Higgs boson to first- and second-generation quarks can be probed by measuring rare decays of the form h->MV, where M denotes a vector meson and V indicates either gamma, W or Z. We calculate the branching ratios for these processes in both the Standard Model and its possible extensions. We discuss the experimental prospects for their observation. The possibility of accessing these Higgs couplings appears to be unique to the high-luminosity LHC and future hadron colliders, providing further motivation for those machines.
Higgs production in association with a photon at hadron colliders is a rare process, not yet observed at the LHC. We show that this process is sensitive to significant deviations of Higgs couplings to first and second generation SM quarks (particularly the up-type) from their SM values, and use a multivariate neural network analysis to derive the prospects of the High Luminosity LHC to probe deviations in the up and charm Higgs Yukawa couplings through $h + gamma$ production.
The fermion mass textures are discussed in the context of F-theory SU(5) GUT. The tree-level up, down and charged lepton Yukawa couplings are computed in terms of the integrals of overlapping wavefunctions at the intersection points of three matter curves. All remaining entries in the fermion mass matrices can also be reliably estimated from higher order non-renormalizable Yukawa couplings mediated by heavy string modes and/or Kaluza-Klein states.
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