ON-SHELL RENORMALIZATION OF FERMION MASSES, FIELDS, AND MIXING MATRICES AT 1-LOOP

In the case of fermion mixing, we propose to use only one of the usual on-shell renormalization conditions at 1-loop and to use off-diagonal mass counterterms. These new counterterms allow for a natural separation of gauge-dependent parts as well as UV divergent parts, for example, the off-diagonal mass counterterms can be chosen to be gauge-independent and to contain all the UV divergences that would otherwise be included in field renormalization. Containment of UV divergences in off-diagonal mass counterterms prevents the migration of said divergences from the mass term to other terms in the Lagrangian. This naturally allows to not associate counterterms with mixing matrices and take them to be always renormalized. In addition, we argue that it is more consistent to not have counterterms for mixing matrices and instead have off-diagonal mass counterterms. Finally, the renormalization scheme is truly universal as it is based on mass structures and also includes absorptive parts where possible.