Top-quark spin correlation at linear colliders with anomalous couplings

We investigate the feasibility of probing anomalous top-quark couplings of Wtb, Zt (t) over bar, and gammat (t) over bar in terms of an effective Lagrangian with dimension-six operators at future e(+)e(-) linear colliders with a c.m. energy roots similar to500-800 GeV. We first examine the constraints on these anomalous couplings from the Z-->b (b) over bar data at CERN LEP I and from unitarity considerations. We then consider in detail the effects of anomalous couplings on t (t) over bar spin correlations in the top-pair production and decay with three spin bases: the helicity, beamline, and off-diagonal bases. Our results show that the polarized beams are more suitable for exploring the effects of different new operators. For polarized beams, the helicity basis yields the best sensitivity.