Twisted mass QCD and lattice approaches to the ΔI=1/2 rule -: art. no. 069

Twisted mass lattice QCD (tmQCD), generalised to four Wilson quark flavours, can be used for the computation of some weak matrix elements related to DeltaI = 1/2 transitions. Besides eliminating unphysical zero modes, tmQCD may alleviate the four-quark operator renormalisation problems encountered in the calculation of CP-conserving K --> pi matrix elements with traditional Wilson fermion regularisation. With an active charm quark, the renormalisation of the K --> pi matrix elements requires at most the subtraction of a linearly divergent counterterm. Furthermore, in the (partially) quenched approximation the twist angles can be chosen so that only a finite counterterm needs to be subtracted.