Perturbative Renormalization of Weak-Hamiltonian Four-Fermion Operators   with Overlap Fermions
  The renormalization of the most general dimension-six four-fermion operators without power subtractions is studied at one loop in lattice perturbation theory using overlap fermions. As expected, operators with different chirality do not mix among themselves and parity-conserving and parity-violating multiplets renormalize in the same way. The renormalization constants of unimproved and improved operators are also the same. These mixing factors are necessary to determine physical matrix elements relevant to many phenomenological applications of weak interactions. The most important are the K0-K0bar and B0-B0bar mixings in the Standard Model and beyond, the Delta I =1/2 rule and epsilon'/epsilon. 
S. Capitani (MIT), L. Giusti (Boston University)