  The effect of the Gribov horizon in Euclidean $SU(2)$ gauge theory is
studied. Gauge fields on the Gribov horizon yield zero modes of ghosts and
anti-ghosts. We show these zero modes can produce additional ghost
interactions, and the Landau gauge changes to a nonlinear gauge effectively. In
the infrared limit, however, the Landau gauge is recovered, and ghost zero
modes may appear again. We show ghost condensation happens in the nonlinear
gauge, and the zero mode repetition is avoided.
