Neutrino mass operator renormalization revisited

We re-derive the renormalization group equation for the effective coupling of the dimension five operator which corresponds to a Majorana mass matrix for the Standard Model neutrinos. We find a result which differs somewhat from earlier calculations, leading to modifications in the evolution of leptonic mixing angles and CP phases. We also present a general method for calculating β-functions from counterterms in MS-like renormalization schemes, which works for tensorial quantities.