Wrinkles in the Froggatt-Nielsen Mechanism and Flavorful New Physics

Abstract

When the Froggatt-Nielsen mechanism is used to explain the Standard Model flavor hierarchy, new physics couplings are also determined by the horizontal symmetry. However, additional symmetries or dynamics in the UV can sometimes lead to a departure from this na\"ive scaling for the new physics couplings. We show that an effective way to keep track of these changes is by using the new spurions of the $\mathrm{U}(3)^5$ global flavor symmetry, where we parameterize extra suppression or enhancement factors, referred to as wrinkles, using the same power counting parameter as in the original Froggatt-Nielsen model. As a concrete realization, we consider two flavor spurions of the $S_1$ leptoquark, and demonstrate that wrinkles can be used to make an enhanced value of $\textrm{BR}(B^+ \to K^+\nu\bar{\nu})$ consistent with other flavor observables. We also present example UV models that realize wrinkles, and comment on choosing consistent charges in ordinary Froggatt-Nielsen models without the typical monotonicity condition.