INFLUENCE OF COSMOLOGICAL TRANSITIONS ON THE EVOLUTION OF DENSITY PERTURBATIONS

We study the influence of the reheating and equality transitions on su perhorizon density perturbations and gravitational waves. Recent criti cisms of the ''standard result'' for large-scale perturbations in infl ationary cosmology are rectified. The claim that the ''conservation la w'' for the amplitude of superhorizon modes was empty is shown to be w rong. For sharp transitions, i.e. the pressure jumps, we rederive the Deruelle-Mukhanov junction conditions. For a smooth transition we come t a result obtained by Grishchuk recently. We show that the junction c onditions are not crucial, because the pressure is continuous during t he reheating transition. The problem occurred because the perturbed me tric was not evolved correctly through the smooth reheating transition . Finally, we derive the ''standard result'' within Grishchuk's smooth (reheating) transition.