Wrinkles in the Froggatt-Nielsen Mechanism and Flavorful New Physics

Understand

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.