Abstract
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.
Highlights
The exploration of new physics at the energy frontier relies on theory guidance to maintain consistency across different experiments, to motivate specific experimental searches and to select promising signatures
If new physics is close to the electroweak (EW) scale, such assumptions must account for the lack of observation of large flavor-changing neutral currents (FCNCs)
Our results provide strong motivation for further developing experimental searches and techniques aiming at identifying new physics coupled mostly to light quarks, such as light-quark taggers [7,8]
Summary
The exploration of new physics at the energy frontier relies on theory guidance to maintain consistency across different experiments, to motivate specific experimental searches and to select promising signatures. While third-generation theory bias is reasonable in the context of many models, the question remains whether one can build successful BSM models where the coupling to light generations is preferred, while maintaining consistency with the results from flavor physics experiments This is important for the exploration of the Higgs sector, as the Higgs boson itself is at the core of the flavor puzzle. To assess the viability of our theories, we perform a comprehensive analysis of flavor and collider bounds of the up-type SFV 2HDM, where Higgs bosons can have large couplings to down, strange and/or bottom quarks. We find that extra Higgses at 100 GeV coupling preferentially to down or strange quarks with Yukawas of order ∼0.1 are allowed by all collider and flavor bounds. In Appendixes B–E we present other technical details, including a full renormalization group equation (RGE) analysis of the SFV structure and a comparison of the SFV 2HDM with other well-known versions of the two-doublet theory
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