SEMICLASSICAL TRANSITION IN PHI(4) THEORY

We show an example of semiclassical transition in phi4 theory with a p ositive coupling constant. This process can be described by the classi cal O(4)-invariant solution, considered on a contour in the complex ti me plane. The transition is technically analogous to the one-instanton transition in the electroweak model. It is suppressed by the factor e xp(-2S0), where S0 is the Lipatov instanton action. This process descr ibes a semiclassical transition between two coherent states with much a smaller number of particles in the initial state than in the final s tate. Therefore, it could be relevant to the problem of the calculatio n of amplitudes for multiparticle production in phi4-type models.