  Critical conjectures on confinement in the Landau gauge is numerically tested
in focus to Gribov copy effects. One of the subjects is of the Kugo-Ojima
confinement criterion and the other is of various viewpoints in the
Gribov-Zwanziger theory. We use the smearing gauge as a reference gauge free of
Gribov copy, and performed three types of simulations, log U, U-linear and log
U in the smearing gauge. It is found that Gribov copy effect on the Kugo-Ojima
parameter is small. log U and U-linear simulations yield only global scale
factor difference in gluon propagator and in ghost propagator, and about 10%
difference in Kugo-Ojima parameter. The horizon function defined by Zwanziger
is evaluated in three types of gauge field and compared. All data show the
negative horizon function as expected.
