Speaker
Description
We discuss a framework based on a local $SU(3)_F$ flavour symmetry in which the observed fermion mass hierarchy and the baryon asymmetry of the Universe arise from the dynamics of flavour symmetry breaking. In the charged-fermion sector, only the third-generation fermions acquire tree-level masses due to a specific choice of field content and gauge charges, while the lighter generations remain unprotected by symmetry and obtain non-vanishing masses through quantum corrections induced by the massive gauge bosons of the broken $SU(3)_F$. An intergenerational hierarchy between the first two families is naturally generated when the flavour symmetry is broken sequentially through an intermediate $SU(2)$ subgroup, leading to a characteristic ordering of the flavour-gauge-boson masses. This mechanism can reproduce realistic charged-fermion masses and quark mixing parameters in terms of not-so-hierarchical fundamental couplings, while generically predicting sizable flavour-changing effects that push the new gauge-boson masses to scales of order $10^3,{\rm TeV}$ or above.
We extend this setup to the neutral-lepton sector by introducing flavour-singlet neutral fermions and a scalar sextet. The sextet generates Majorana masses for the $SU(3)_F$-triplet right-handed neutrinos after flavour symmetry breaking, whereas the singlet fermions provide a seesaw portal to the active neutrinos. The resulting neutral-fermion sector has the structure of an extended seesaw, in which the singlet and triplet Majorana states mix after $SU(3)_F$ breaking. At tree level, the minimal singlet-mediated seesaw gives a rank-one active-neutrino mass matrix, while the broken flavour gauge sector and additional flavour-breaking structures can radiatively lift the remaining neutrino masses. The same heavy neutral fermion sector may provide new sources of lepton-number violation and CP violation, enabling leptogenesis through the out-of-equilibrium decays of mixed singlet–triplet Majorana states. This framework therefore can link the origin of fermion mass hierarchies, neutrino masses, and the cosmological baryon asymmetry to the breaking pattern of a gauged $SU(3)_F$ symmetry.