Probing top-quark couplings at polarized NLC

The energy spectrum of the lepton(s) in e(+)e(-)-t (t) over bar -->l(+/-).../l(+)l(-)... at next linear colliders (NLC's) is studied for arbitrary longitudinal beam polarizations as a test of possible new physics in top-quark couplings. The most general nonstandard form factors are assumed for gamma t (t) over bar, Zt (t) over bar, and Wtb vertices to analyze new-physics effects in a model-independent way. The expected precision in determining these form factors is estimated applying the optimal-observable procedure to the spectrum.