Renormalizable Models of Flavor-Specific Scalars

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.