EVIDENCE FOR HARD CHIRAL LOGARITHMS IN QUENCHED LATTICE QCD

We present the first direct evidence that quenched QCD differs from full QCD in the chiral(m(q)-->0) limit, as predicted by chiral perturbation theory, from our quenched lattice QCD simulations at beta = 6/g(2) = 6.0. We measure the spectrum of light hadrons on 16(3) x 64, 24(3) x 64, and 32(3) X 64 lattices, using staggered quarks of masses m(q) = 0.01, m(q) = 0.005, and m(q) = 0.0025. The pion masses show evidence for logarithmic violations of the PCAC relation m(pi)(2) alpha m(q), as predicted by quenched chiral perturbation theory. The dependence on spatial lattice volume precludes this being a finite size effect. No evidence is seen for such chiral logarithms in the behavior of the chiral condensate [($) over bar psi psi].