K → ππ matrix elements from mixed action lattice QCD

We present a new method for determining K → ππ matrix elements from lattice simulations that is less costly than direct simulations of K → ππ at physical kinematics. It improves, however, upon the traditional “indirect” approach of constructing the K → ππ matrix elements using NLO SU(3) χPT, which can lead to large higher-order chiral corrections. Using the explicit example of the ∆I = 3/2 (27,1) operator to illustrate the method, we obtain a value for Re(A₂) that agrees with experiment and has a total uncertainty of _∼ ^< 20%. Although our simulations use domain-wall valence quarks on the MILC asqtad-improved gauge configurations, this method is more general and can be applied to calculations with any fermion formulation.