Canonical quantization of nonlinear waves

By means of a canonical transformation we investigate nonlinear field theories that possess exact classical solutions. This transformation is equivalent to the method of collective coordinates recently applied to the same problem by Gervais and Sakita using functional techniques. It is pointed out that, because of the operator orderings, extra terms occur in the quantized theory which seem to be absent in the straightforward functional approach. Ordinary perturbation treatment of the resulting Hamiltonian reproduces results previously obtained by Goldstone and Jackiw using a different technique.