Informal Pizza Seminar

Symmetry of Leptonic Generations

C.S. Lam

McGill/UBC

Symmetry has played a central role in constructing particle physics theories, from the Standard Model, to the Grand Unified Theory, to Supersymmetry, and String Theories. For that reason it is reasonable to suppose that the relations between the three generations of fermions can be understood by symmetry as well. To that end the first question to answer is what is the correct (horizontal) symmetry for the generation structure. Starting from the experimental data on neutrino mixing, I deduce that the unique symmetry is S₄, the permutation group of four objects. Possible experimental signature for the presence of horizontal symmetry is also discussed.