Quark loop effects with an improved staggered fermion action

We have been studying effects of dynamical quarks on various hadronic obser vables, using our recently formulated improvement for staggered fermions. T o illustrate improvement, we show that the light hadron spectrum in the que nched approximation gives remarkably good scaling. We highlight three new r esults: (1) We find no apparent quark loop effects in the Edinburgh plot wi th 2+1 flavors of dynamical quarks at a = 0.14 fm. (2) We show that dynamic al quarks modify the shape of the heavy quark potential. (3) we present res ults hinting at meson decay effects in light hadron spectroscopy.