Covariant method for calculating helicity amplitudes

We present an alternative approach for calculating helicity amplitudes for processes involving both massless and massive fermions. With this method one can easily obtain covariant expressions for the helicity amplitudes. The final expressions involve only four-vector products and are independent of the basis for γ matrices or specific form of the spinors. We use the method to obtain the helicity amplitudes for several processes involving top quark production. copyright 1996 The American Physical Society