ISOSPIN BREAKING AND FINE-TUNING IN TOP-COLOR ASSISTED TECHNICOLOR

Recently, Hill has proposed a model in which new, potentially low-ener gy, top-color interactions produce a top-condensate (a la Nambu-Jona-L asinio) and accommodate a heavy top quark, while technicolor is respon sible for producing the W and Z masses. Here we argue that isospin bre aking gauge interactions, which are necessary in order to split the to p and bottom quark masses, are likely to couple to technifermions. In this case they produce a significant shift in the W and Z masses (i.e. contribute to Delta rho = alpha T) if the scale of the new interacti ons is near 1 TeV. In order to satisfy experimental constraints on Del ta rho, we find that either the effective top quark coupling or the t op-color coupling must be adjusted to 1%. Independent of the couplings of the technifermions, we show that the isospin-splitting of the top and bottom quarks implies that the top-color gauge bosons must have ma sses larger than about 1.4 TeV. Our analysis can also be applied to st rong extended technicolor (ETC) models that produce the top-bottom spl itting via isospin breaking ETC interactions.