We extend our recent unquenched (Nf=2+1 flavor) calculation of BK using improved staggered fermions by including in the fits the finite volume shift predicted by one-loop staggered chiral perturbation theory. The net result is to lower the result in the continuum limit by 0.6%. This shift is slightly smaller than our previous estimate of finite volume effects based on a direct comparison between different volumes. To include the finite volume effects in a reasonable time, we found it necessary to calculate them using Graphics Processing Units.
@article{arxiv.1101.2685,
title = {Finite volume effects in $B_K$ with improved staggered fermions},
author = {Jangho Kim and Chulwoo Jung and Hyung-Jin Kim and Weonjong Lee and Stephen R. Sharpe},
journal= {arXiv preprint arXiv:1101.2685},
year = {2011}
}