Non-commuting ETC corrections to zt\bar{t} vertex
  In this paper we calculate the corrections to zt\bar {t} couplings induced by non-commuting ETC interactions. The extra parameters \delgbl, s^2 and {1\over x} of non-commuting ETC models and the usual SM parameters will be be assumed to be determined from a global fit to the LEP 1 EW data. We find that in the heavy (light) case F^t_L is modified by at most 4% (2.8%) relative to its SM value provided \delrb < .0088. This implies that it will be very difficult to disentangle the ETC corrections from SM corrections to zt\bar {t} vertex or to probe the effects of non-commuting ETC on zt\bar {t} couplings with the projected NLC precision of measuring them. 
Uma Mahanta