Abstract
New light singlet scalars with flavor-specific couplings represent a phenomenologically distinctive and flavor-safe alternative to the well-studied possibility of Higgs-portal scalars. However, in contrast to the Higgs portal, flavor-specific couplings require an ultraviolet completion involving new heavy states charged under the Standard Model gauge symmetries, leading to a host of additional novel phenomena. Focusing for concreteness on a scenario with up quark-specific couplings, we investigate two simple renormalizable completions, one with an additional vector-like quark and another featuring an extra scalar doublet. We consider the implications of naturalness, flavor- and CP-violation, electroweak precision observables, and direct searches for the new states at the LHC. These bounds, while being model-dependent, are shown to probe interesting regions in the parameter space of the scalar mass and its low-energy effective coupling, complementing the essential phenomenology of the low-energy effective theory at a variety of low and medium energy experiments.
Highlights
Light dark sectors that couple weakly to the Standard Model (SM) may address some of the key open questions in particle physics today [1,2,3]
This point has been illustrated in previous studies of light hadrophilic dark matter based on an up-specific scalar mediator [12] and a possible explanation of the muon anomalous magnetic moment discrepancy [13,14] based on a muon-specifc scalar mediator [9]
We study the phenomenology of the model, including the impact of Cabibbo– Kobayashi–Maskawa (CKM) unitarity, flavor changing neutral currents (FCNCs), electroweak precision test (EWPTs), CP violation, and searches at the LHC
Summary
One can circumvent this issue by appealing to a flavor hypothesis on the structure of the scalar mediator couplings, devised so as to suppress FCNCs at tree level In this regard, scalar mediators respecting the flavorspecific hypothesis provide an interesting alternative to the Higgs portal [9] If the singlet couples preferentially to first or second generation states, this scenario leads to a distinctive phenomenology compared to the Higgs portal model This point has been illustrated in previous studies of light hadrophilic dark matter based on an up-specific scalar mediator [12] and a possible explanation of the muon anomalous magnetic moment discrepancy [13,14] based on a muon-specifc scalar mediator [9]. Appendix A describes the flavor hypothesis for each renormalizable completion, while Appendix B provides details of the physical interactions in the VLQ completion
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