The Curvaton Web

TL;DR

The paper uncovers a web-like spatial structure for curvaton-induced perturbations, showing that the observable universe can inhabit regions with vastly different Gaussianity depending on the relative scales l0 and lH. It highlights a crucial reheating effect: production of curvaton particles can suppress the curvaton’s contribution to density perturbations and even enhance non-Gaussianity, introducing a tunable parameter via reheating. By examining curvaton-inflaton transmutation and connections to eternal inflation and the string landscape, the authors demonstrate both the potential explanatory power and the model-dependence of the curvaton mechanism. Overall, the work provides a conceptual and quantitative framework for how multi-field dynamics and early-universe processes could shape the large-scale structure and its statistical properties across a multivalent cosmos.

Abstract

We discuss nontrivial features of the large scale structure of the universe in the simplest curvaton model proposed in our paper astro-ph/9610219. The amplitude of metric perturbations in this model takes different values in different parts of the universe. The spatial distribution of the amplitude looks like a web consisting of exponentially large cells. Depending on the relation between the cell size l_0 and the scale of the horizon l_H, one may either live in a part of the universe dominated by gaussian perturbations (inside a cell with l_0 >> l_H), or in the universe dominated by nongaussian perturbations (for l_0 << l_H). We show that the curvaton contribution to the total amplitude of adiabatic density perturbations can be strongly suppressed if the energy density of the universe prior to the curvaton decay was dominated not by the classical curvaton field but by the curvaton particles produced during reheating. We describe the curvaton-inflaton transmutation effect: The same field in different parts of the universe may play either the role of the curvaton or the role of the inflaton. Finally, we discuss an interplay between the curvaton web and anthropic considerations in the string theory landscape.

Figures (3)

• Figure 1: Results of a computer simulation of the Bunch-Davies distribution of the curvaton field $\sigma$ for $H/m = 3$. For greater values of $H/m$ the typical height of the hills grow as $H^{2}/m$, and a typical size of the 'islands' grows as $H^{-1} \exp\Bigl(O\Bigl({\frac{H^2}{m^2}}\Bigr)\Bigr)$. In order to make the level $\sigma=0$ clearly visible, we show only the part of the 'curvaton landscape' with $\sigma > 0$, i.e. above the 'sea level' $\sigma = 0$. As we will show below, the amplitude of the curvaton density perturbations behaves in a rather peculiar way near the 'shoreline' $\sigma = 0$, see Figs. \ref{['fig:Figa']} and \ref{['fig:Figb']}.
• Figure 2: The spatial distribution of the square of the amplitude of density perturbations near the walls $\sigma = 0$, for $C<H^{2}/m$. The amplitude of density perturbations vanishes at the walls $\sigma = 0$. These walls are surrounded from both sides by the walls where the amplitude of density perturbations reaches its maximal value.
• Figure 3: Contour plot for the square of the amplitude of the density perturbations shown at the previous figure. White regions correspond to vanishing amplitude of density perturbations, black regions correspond to maximal absolute values of density perturbations. This figure confirms that the two walls with large amplitude of density perturbations (see Fig. \ref{['fig:Figa']}) surround the domain boundaries with $\sigma = 0$ where the amplitude of density perturbations vanishes. (At the previous figure, the regions with $\sigma = 0$ were hidden by the walls.)