Quark Loop Effects with an Improved Staggered Action
  We have been studying effects of dynamical quarks on various hadronic observables, using our recently formulated improvement for staggered fermions. To illustrate improvement, we show that the light hadron spectrum in the quenched approximation gives remarkably good scaling. We highlight three new results: (1) We find no apparent quark loop effects in the Edinburgh plot with 2+1 flavors of dynamical quarks at a = 0.14 fm. (2) We show that dynamical quarks modify the shape of the heavy quark potential. (3) We present results hinting at meson decay effects in light hadron spectroscopy. 
MILC Collaboration: C. Bernard (1), T. Burch (2), T.A. DeGrand (3),   C.E. DeTar (4), Steven Gottlieb (5), U.M. Heller (6), ...