Finite volume effects in $B_K$ with improved staggered fermions

Understand

We extend our recent unquenched ($N_f=2+1$ flavor) calculation of $B_K$ 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.