ISOCURVATURE PERTURBATIONS IN MULTIPLE INFLATIONARY MODELS

The dynamics of long-wave isocurvature perturbations during an inflati onary stage in multiple (multicomponent) inflationary models is calcul ated analytically for the case where scalar fields producing this stag e interact among themselves through gravity only. This enables us to d etermine the correct amplitudes of such perturbations produced by vacu um quantum fluctuations of the scalar fields during the multiple infla tionary stage. An exact matching to a post-inflationary evolution that gives the amplitude of isocurvature perturbations in the cold dark ma tter model with radiation is performed in the case where a massive inf laton held remains uncoupled from usual matter up to the present time. For this model, isocurvature perturbations are smaller than adiabatic ones in the region of the break in the perturbation spectrum which ar ises due to a transition between the two phases of inflation, but they may be much bigger and have a maximum at much shorter scales. The cas e of an inflation with a quartic coupling that remains uncoupled after inflation is considered, too.