ΔS=2 and ΔC=2 bag parameters in the standard model and beyond from Nf=2+1+1 twisted-mass lattice QCD

We present unquenched lattice QCD results for the matrix elements of four-fermion operators relevant to the description of the neutral K and D mixing in the standard model and its extensions. We have employed simulations with Nf=2+1+1 dynamical sea quarks at three values of the lattice spacings in the interval 0.06-0.09 fm and pseudoscalar meson masses in the range 210-450 MeV. Our results are extrapolated to the continuum limit and to the physical pion mass. Renormalization constants have been determined nonperturbatively in the RI-MOM scheme. In particular, for the kaon bag parameter, which is relevant for the K¯0-K0 mixing in the standard model, we obtain BKRGI=0.717(24).