One-loop matching of Delta S=2 four-quark operators with improved   staggered fermions
  We compute O(alpha_s) lattice-to-continuum perturbative matching coefficients for the Delta S=2 flavor changing four-quark operators for the Asqtad improved staggered action. In conjunction with lattice simulations with three flavors of light, dynamical quarks, our results yield an unquenched determination of B_K, the parameter that determines the amount of indirect CP violation in the neutral kaon system. Its value is an important input for the unitarity triangle analysis of weak decays. 
Thomas Becher (Fermilab), Elvira Gamiz (Glasgow U.), Kirill Melnikov   (Hawaii U.)