Mixing at 1-loop for quasi-degenerate fermions in a SU(2)_L gauge theory of weak interactions

Bruno Machet (1)

1 LPTHE - Laboratoire de Physique Théorique et Hautes Energies

1-loop transitions induce diagonal and non-diagonal kinetic-like, momentum (p^2) dependent interactions between fermionic bare mass eigenstates. We correspondingly re-examine the Cabibbo procedure, which requires in particular the simultaneous re-diagonalization of kinetic and mass terms. When two fermions get close to degeneracy, a resonance exists, at which the ``Cabibbo'' angle becomes close to maximal and is simply connected with the masses of all four fermions inside the concerned two generations and to that of the W gauge boson. It proves also, then, the closest to its classical value. Mass splittings are furthermore shown to make slightly non-unitary the connection between bare flavor (or mass) states and 1-loop mass eigenstates. Still, the 1-loop Cabibbo (PMNS) matrix, the expression of which is dictated by gauge invariance, stays unitary.

Mots clés: mixing; radiative corrections; mass-splitting

Domaines: Physique des Hautes Energies - Phénoménologie [hep-ph]

Bruno Machet. Mixing at 1-loop for quasi-degenerate fermions in a SU(2)_L gauge theory of weak interactions. 2009. ⟨hal-00422646v2⟩