K \to \pi\pi decay amplitudes from the lattice
  In order to directly compute physical two-pion K-decay amplitudes using lattice methods we must prepare a two-pion state with non-zero relative momentum. Building upon a proposal of Lellouch and L\"uscher, we describe a finite-volume method to realize such a state as the lowest energy state of two pions. 
Changhoan Kim, Norman H. Christ