Speaker: Roberto Mattacchione (Roma Sapienza Univ.)

The fermion mass hierarchy remains one of the most glaring puzzles of the Standard Model (SM). A prominent framework to address this is the Froggatt-Nielsen (FN) mechanism, where hierarchical Yukawa couplings originate from a spontaneously broken
flavor symmetry. In this setup, effective higher-dimensional operators generate fermion masses after heavy vector-like fermions are integrated out. This work systematically evaluates the phenomenological viability of various FN charge textures. We demonstrate that the top and bottom quark masses impose the most stringent constraints, and we introduce a novel analytical method to estimate the FN parameters directly from specific charge assignments. To quantify the naturalness of these scenarios, we define measures of fine-tuning for both individual observables and entire models. Our analysis reveals that reproducing SM phenomenology without extreme fine-tuning requires non-trivial FN configurations. Finally, we establish a robust set of diagnostic tests to evaluate a texture’s viability and apply them to several models from the literature. We find that while minimal textures are generally insufficient, non-minimal textures featuring larger charge separations successfully reproduce SM data. The implications for gauge coupling running and potential ultraviolet (UV) completions are also discussed.