Quark Lagrangian diagonalization versus non-diagonal kinetic terms
  Loop corrections induce a dependence on the momentum squared of the coefficients of the Standard Model Lagrangian, making highly non-trivial (or even impossible) the diagonalization of its quadratic part. Fortunately, the introduction of appropriate counterterms solves this puzzle. 
Quentin Duret (LPTHE), Bruno Machet (LPTHE), M. I. Vysotsky (ITEP)