Rotational invariance in light-cone quantization

In the study of the decay of a heavy scalar particle at rest in the Yukawa model at the one- and two-loop levels, it is shown explicitly that naive light-cone quantization leads to a violation of rotational invariance. Noncovariant counterterms are constructed in detail to restore Lorentz covariance. An analysis of surface and zero-mode contributions clarifies the origin of the problem.