NONPERTURBATIVE QUANTUM DYNAMICS OF A NEW INFLATION MODEL

We consider an O(N) model coupled self-consistently to gravity in the semiclassical approximation, where the field is subject to ''new infla tion'' type initial conditions. We study the dynamics self-consistentl y and non-perturbatively with non-equilibrium field theory methods in the large N limit. We find that spinodal instabilities drive the growt h of non-perturbatively large quantum fluctuations which shut off the inflationary growth of the scale factor. We find that a very specific combination of these large fluctuations plus the inflaton zero mode as semble into a new effective field. This new field behaves classically and it is the object which actually rolls down. We show how this reint erpretation saves the standard picture of how metric perturbations are generated during inflation and that the spinodal growth of fluctuatio ns dominates the time dependence of the Bardeen variable for superhori zon modes during inflation. We compute the amplitude and index for the spectrum of scalar density and tensor perturbations and argue that in all models of this type the spinodal instabilities are responsible fo r a ''red'' spectrum of primordial scalar density perturbations. A cri terion for the validity of these models is provided and contact with t he reconstruction program is established validating some of the result s within a non-perturbative framework. The decoherence aspects and the quantum to classical transition through inflation are studied in deta il by following the full evolution of the density matrix and relating the classicality of cosmological perturbations to that of long-wavelen gth matter fluctuations. [S0556-2821(98)03804-1].