Effects of nonperturbatively improved dynamical fermions in QCD at fixed lattice spacing

We present results for the static interquark potential, lightest glueballs, light hadron spectrum, and topological susceptibility using a nonperturbatively improved action on a 16³×32 lattice at a set of values of the bare gauge coupling and bare dynamical quark mass chosen to keep the lattice size fixed in physical units (∼1.7 fm). By comparing these measurements with a matched quenched ensemble, we study the effects due to two degenerate flavors of dynamical quarks. With the greater control over residual lattice spacing effects which these methods afford, we find some evidence of charge screening and some minor effects on the light hadron spectrum over the range of quark masses studied (M_PS/M_V>~0.58, where PS denotes pseudoscalar and V denotes vector). More substantial differences between quenched and unquenched simulations are observed in measurements of topological quantities.