  String breaking by dynamical quarks in three-dimensional lattice QCD is
analyzed through measurements of the potential and the local color-electric
field strength generated by a static quark-antiquark pair. Simulations were
done for unquenched SU(2) color with two flavors of staggered light quarks. An
improved gluon action was used, which allows simulations to be done on coarse
lattices, providing an extremely efficient means to access the large quark
separations and long propagation times at which string breaking occurs. The
static sources were generated using Wilson loop operators, hence no light
valence quarks are present in the resulting trial states. Results give
unambiguous evidence of string breaking. First the static potential is shown to
saturate at twice the heavy-light meson mass at large separations. Then it is
demonstrated that the local color-electric field strength in the region between
the heavy quarks tends towards vacuum values at large separations, the first
time that this most graphic effect of quark vacuum polarization on the
confining flux-tube has been realized in lattice QCD. Implications of these
results for unquenched simulations of four-dimensional QCD are drawn.
