Isocurvature, non-gaussianity and the curvaton model

TL;DR

This paper re-analyzes the curvaton model, showing that large local non-gaussianity implies negligible isocurvature perturbations, which constrains the timing of CDM creation and the inflation scale.

Contribution

It demonstrates that significant non-gaussianity in the curvaton scenario requires the absence of isocurvature modes, leading to new constraints on CDM formation timing and inflation scale.

Findings

Large non-gaussianity implies zero isocurvature in the curvaton model.

CDM must be created after curvaton decay to avoid isocurvature.

Constraints relate the universe's temperature at CDM creation to inflation scale.

Abstract

Recent analyses of the statistical distribution of the temperature anisotropies in the CMB do not rule out the possibility that there is a large non-gaussian contribution to the primordial power spectrum. This fact motivates the re-analysis 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 CMB. 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 CDM must be created at a late stage, after the curvaton decays completely. This requirement is used to constrain the nature of the CDM in this scenario, arriving at a general relation between the temperature of the universe at CDM creation and the scale of inflation.