CHAOS IN EFFECTIVE CLASSICAL AND QUANTUM DYNAMICS OF NONLINEAR OSCILLATORS

We investigate the dynamics of classical and quantum N-component phi(4 ) oscillators in presence of an external field. In the large N limit t he effective dynamics is described by two-degree-of-freedom classical Hamiltonian systems. In the classical model we observe chaotic orbits for any value of the external field, while in the quantum case chaos i s strongly suppressed. A simple explanation of this behaviour is found in the change in the structure of the orbits induced by quantum corre ctions. Consistently with Heisenberg's principle, quantum fluctuations are forced away from zero, removing in the effective quantum dynamics a hyperbolic fixed point that is a major source of chaos in the class ical model.