The primordial density perturbation in the curvaton scenario

TL;DR

This work analyzes a curvaton-based origin for the primordial density perturbation, outlining how curvaton perturbations are transferred into the total curvature and how this framework accommodates both adiabatic and isocurvature modes, as well as potentially large non-Gaussianity. It derives the transfer mechanism between curvaton perturbations and the curvature perturbation via a transfer parameter r, yielding the key relation ${\cal P}^{1/2}_\zeta=(2/3) r {\cal P}^{1/2}_{\delta\sigma/\sigma}$ and the non-Gaussianity parameter ${\cal N}_{\rm NL}=f_{\rm NL}=5/(4r)$; observational bounds on non-Gaussianity thus translate into lower limits on r. The paper then analyzes residual isocurvature perturbations in CDM, baryons, and neutrinos, showing that pre-decay CDM creation is strongly disfavored while baryon and neutrino sectors can yield testable signatures depending on lepton asymmetry and curvaton decay timing. It concludes that MAP/Planck data will be crucial for confirming or falsifying curvaton-induced non-Gaussianity and correlated isocurvature components, with distinct predictions across matter and neutrino sectors.

Abstract

We analyse the primordial density perturbation when it is generated by a `curvaton' field different from the inflaton. In some cases this perturbation may have large isocurvature components, fully correlated or anti-correlated with the adiabatic component. It may also have a significant non-Gaussian component. All of these effects are calculated in a form which will enable direct comparison with current and forthcoming observational data.