Generating cosmological perturbations with mass variations

Abstract

We study the possibility that large scale cosmological perturbations have been generated during the domination and decay of a massive particle species whose mass depends on the expectation value of a light scalar field. We discuss the constraints that must be imposed on the field in order to remain light and on the annihilation cross section and decay rate of the massive particles in order for the mechanism to be efficient. We compute the resulting curvature perturbations after the mass domination, recovering the results of Dvali, Gruzinov, and Zaldarriaga in the limit of total domination. By comparing the amplitude of perturbations generated by the mass domination to those originally present from inflation, we conclude that this mechanism can be the primary source of perturbations only if inflation does not rely on slow-roll conditions.