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Lattice QCD with 8 and 12 degenerate quark flavors

We compare extensive simulations of QCD with 8 and 12 flavors of degenerate quarks, using the DBW2 gauge action, naive staggered fermions, and the rational hybrid Monte Carlo algorithm. A variety of values of the coupling constant, quark mass, and lattice size have been used. Our data suggests that, as the bare coupling is decreased, a rapid cross-over, which dramatically changes the lattice scale, exists with both 8 and 12 flavors. The scale change across this cross-over is much larger with 12 flavors than it is with 8 flavors. All of the observables we have measured, in both the zero and finite temperature systems, are consistent with a chiral symmetry breaking phase for the zero temperature theory on the weak coupling side of the rapid cross-over.