Perturbative renormalization factors of four-quark operators for   improved Wilson fermion action and Iwasaki gauge action
  The renormalization factor and O(a) improvement coefficient of four-quark operators are calculated perturbatively for the improved Wilson fermion action with clover term and the Iwasaki gauge action. With an application to the $K\to\pi\pi$ decay amplitude in mind, the calculation is restricted to the parity odd operator, for which the operators are multiplicatively renormalized without any mixing to operators that have different chiral structures. 
Yusuke Taniguchi
hep-lat