We do not know why there are three fermion families in the Standard Model, nor can we explain the observed pattern of fermion masses and mixing angles. Standard grand unified theories based on the SU(5) and SO(10) groups fail to shed light on this issue, since they also contain three copies of fermion representations of an enlarged gauge group.
However, it does not need to be so. In this talk, I will discuss the possibility that the Standard Model families are distributed over distinct representations of a grand unified model, in which case the gauge symmetry itself might discriminate the various families and explain (at least partially) the flavor puzzle.
The most ambitious implementation of this idea consists on embedding all fermions in a single irreducible representation of a large gauge group. Flavor would then be an effective phenomena, emerging at low energies from a fundamental theory with no fermion family replication.
With support from FCT through project UIDB/00777/2020