SEMICLASSICAL SCATTERING IN YANG-MILLS THEORY

A classical solution to the Yang-Mills theory is given a semiclassical interpretation. The boundary value problem on a complex time contour which arises from the semiclassical approximation to multiparticle sca ttering amplitudes is reviewed and applied to the case of Yang-Mills t heory. The solution describes a classically forbidden transition betwe en states with a large average number of particles in the limit g --> 0. It dominates a transition probability with a semiclassical suppress ion factor equal to twice the action of the well-known BPST instanton. Hence, it is relevant to the problem of high-energy tunnelling. It de scribes transitions of unit topological charge for an appropriate time contour. Therefore, it may have a direct interpretation in terms of f ermion-number violating processes in electroweak theory. The solution describes a transition between an initial state with parametrically fe wer particles than the final state. Thus, it may be relevant to the st udy of semiclassical initial-state corrections in the limit of a small number of initial particles. The implications of these results for mu ltiparticle production in electroweak theory are also discussed.