Isocurvature, non-Gaussianity, and the curvaton model

Abstract

Recent analyses of the statistical distribution of the temperature anisotropies in the cosmic microwave background do not rule out the possibility that there is a large non-Gaussian contribution to the primordial power spectrum. This fact motivates the reanalysis of the curvaton scenario, paying special attention to the compatibility of large non-Gaussianity of the local type with the current detection limits on the isocurvature amplitude in the cosmic microwave background. We find that if the curvaton mechanism generates a primordial power spectrum with an important non-Gaussian component, any residual isocurvature imprint originated by the curvaton, would have an amplitude too big to be compatible with the current bounds. This implies that the isocurvature mode should be equal to zero in this scenario and we explore the consequences of this inference. In order to prevent the generation of a such a signal, the cold dark matter (CDM) must be created at a late stage, after the curvaton decays completely. This is used to constrain the nature of the CDM, arriving at a general relation between the temperature of the universe at CDM creation and the scale of inflation. It is possible to find an absolute maximum for the temperature at CDM creation, which is dependent on the particular inflationary potential. For a quadratic potential, we find ${T}_{\mathrm{cdm}}l1.7\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\mathrm{GeV}$.