Phenomenology of the top mass in realistic extended technicolor models

Extended technicolor (ETC) theories typically require ETC gauge bosons lighter than of order 1 TeV, to perturbatively generate the t quark mass. We point out that explicit models of t − b mass splitting also typically contain additional TeV scale ETC gauge bosons transforming in the adjoint of technicolor, leading to large weak-isospin-breaking effects observable in the ϱ parameter. Viable ETC models may thus require a lowest ETC scale of order 10 TeV, with relatively strong and finely tuned couplings to generate mt. Such models do not generate observable corrections to the Zbb vertex.