Abstract

The existence of three generations of Standard Model (SM) fermions, and the hierarchical structure observed in their Yukawa couplings to the Higgs, are two long-standing mysteries in particle physics. I will discuss recent theoretical ideas for solving this "flavour puzzle", focussing on the model of Electroweak Flavour Unification which postulates that the three generations start life as one particle at high energies. Like other BSM theories that explain flavour, this model predicts new particles that couple strongly to the heavy generations. In particular, the lightest new particles are heavy copies of the W and Z bosons with flavour non-universal couplings to the second and third family.