Theoretical Aspects of Flavour and CP Violation in the Lepton Sector

Abstract

We review flavour and CP violations in the lepton sector as probes of new physics beyond the standard model and its minimal extensions accommodating massive neutrinos. After recalling the main experimental bounds and the future perspectives, we summarize the limits on a set of dimension-six gauge-invariant operators, pointing to a scale of new physics much larger than the electroweak scale. If we insist on having new physics at the TeV scale, as demanded by most of the standard model extensions addressing the gauge hierarchy problem, we should rely on special mechanisms to deplete flavour and CP violations in the charged lepton sector. We comment on the capability of partial compositeness in reconciling the absence of signals with a scale of new physics accessible to the LHC.