Dynamical determination of B_K from improved staggered quarks
  The scaling corrections that affected previous staggered calculations of B_K have been proved to be reduced by using improved actions (HYP, Asqtad) in the quenched approximation. This improved behaviour allows us to perform a reliable dynamical calculation of B_K including quark vacuum polarization effects using the MILC (2+1) flavour dynamical configurations. We report here on the results from such dynamical calculation. We also discuss the renormalization effects with the Asqtad action. 
E. Gamiz, S. Collins, C. T. H. Davies, J. Shigemitsu, M. Wingate   (HPQCD and UKQCD collaborations)