  The nontrivial boundary conditions (BC's) for the Topcolor breaking are
investigated in the context of the TeV-scale extra dimension scenario. In the
gauge symmetry breaking mechanism via the BC's we do not need to incorporate a
dynamical mechanism for the Topcolor breaking into the model. Moreover, the
Topcolor breaking can be realized without introducing explicitly a (composite)
scalar field. We present a six dimensional model where the top and bottom
quarks in the bulk have the Topcolor charge while the other quarks in the bulk
do not. We also put the electroweak gauge interaction in the six dimensional
bulk. The bottom quark condensation is naturally suppressed owing to the
power-like running of the bulk U(1)_Y interaction, so that only the top
condensation is expected to take place. We explore such a possibility based on
the ladder Schwinger-Dyson equation and show the cutoff to make the model
viable.
