Lattice QCD without tuning, mixing and current renormalization

Abstract

The classically perfect action of QCD requires no tuning to get the pion massless in the broken phase: the critical bare mass $m_q^c$ is zero. Neither the vector nor the flavour non-singlet axial vector currents need renormalization. Further, there is no mixing between four-fermion operators in different chiral representations. The order parameter of chiral symmetry requires, however, a subtraction which is given here explicitly. These results are based on the fact that the fixed point action satisfies the Ginsparg-Wilson remnant chiral symmetry condition. On chiral symmetry related questions any other local solution of this condition will produce similar results.