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 vectorlike 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 lowenergy effective coupling, complementing the essential phenomenology of the low-energy effective theory at a variety of low and medium energy experiments.