Lepton Flavour Symmetries

Abstract

We provide a general classification of flavour symmetries according to their interplay with the proper Poincare' and gauge groups and to their linear or nonlinear action in field space. We focus on the lepton sector and we review the different types of symmetries describing neutrino masses and the lepton mixing matrix. For each type of symmetry we present several illustrative examples and we discuss specific strengths and limitations.

Comments: 70 pages, 5 figures. Added extensive comments on the quark sector and new references. Version accepted for publication on Review of Modern Physics