EVIDENCE FOR HARD CHIRAL LOGARITHMS IN QUENCHED LATTICE QCD

We present the first direct evidence that quenched QCD differs from fu ll QCD in the chiral(m(q)-->0) limit, as predicted by chiral perturbat ion 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), a s predicted by quenched chiral perturbation theory. The dependence on spatial lattice volume precludes this being a finite size effect. No e vidence is seen for such chiral logarithms in the behavior of the chir al condensate [($) over bar psi psi].