FORMULATION OF BARYON NUMBER VIOLATING COLLISIONS - THE CASE OF O(3) NONLINEAR SIGMA-MODEL

A new formalism based on path-integral expression of time-evolution operator during tunneling is presented. Instead of instanton calculus in the LSZ formalism, a classical bounce solution leading to sphaleron (instanton action) at high (low) energies is adopted adopted as the tunneling configuration. The formalism is applied to O(3) nonlinear sigma model in two dimensions. For the coupling constant g2 congruent-to 0.1, which may be physical in the sense that the number of produced particles congruent-to 100, comparable with that of electroweak theory, the baryon number violating cross section is smaller by orders of magnitude than the so-called unitarity bound.