Dynamical Yukawa Couplings

Abstract

The matter content of the Standard Model admits a global symmetry due to the generational structure of the spectrum respected by all interactions except for fermion couplings to the Higgs doublet. This symmetry is identified as the largest possible global symmetry of the free theory and extended to the case of massive neutrinos. The violation of such symmetry is then assumed dynamical and the value of the Yukawa couplings is fixed by a variational principle. This ansatz yields compelling results: Quark Yukawas naturally accommodate hierarchical masses and small mixing whereas Lepton Yukawas exhibit a hierarchical pattern for charged leptons and simultaneously degeneracy in the neutrino sector correlated with large mixing and Majorana phases. The difference in the mixing patterns of Quark and Leptons in this scheme stem from the Dirac vs Majorana nature of fermions.