2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/181626We apply finite-size recursion techniques based on the Schrodinger functional formalism to determine the renormalization group running of four-fermion operators which appear in the Delta S=2 effective weak Hamiltonian of the Standard Model. Our calculations are done using O(a) improved Wilson fermions with N_f=2 dynamical flavours. Preliminary results are presented for the four-fermion operator which determines the B_K parameter in tmQCD.7 pages, 2 figures, talk presented at Lattice2006 (Renormalization)High Energy Physics - Latticetext