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The simplest curvaton model

N Bartolo, Andrew R Liddle

TL;DR

The paper presents a concrete, minimal curvaton model in which isocurvature perturbations of a subdominant scalar field are converted into adiabatic, nearly scale-invariant curvature perturbations after inflation. By analyzing a two-field quadratic potential and deriving the curvature perturbation amplitude in regimes where the curvaton decays before or after dominating the energy density, the authors map the viable parameter space under both prompt and prolonged reheating scenarios. They demonstrate that Gaussian, adiabatic perturbations consistent with observations can be obtained within restricted regions of the four-parameter space {m, M, σ*, Γσ}, and highlight that the model generically predicts a low amplitude for primordial gravitational waves. The work provides a complete constraint set for the simplest curvaton realization and discusses its observational implications and degeneracy with inflationary predictions.

Abstract

We analyze the simplest possible realization of the curvaton scenario, where a nearly scale-invariant spectrum of adiabatic perturbations is generated by conversion of an isocurvature perturbation generated during inflation, rather than the usual inflationary mechanism. We explicitly evaluate all the constraints on the model, under both the assumptions of prompt and delayed reheating, and outline the viable parameter space.

The simplest curvaton model

TL;DR

The paper presents a concrete, minimal curvaton model in which isocurvature perturbations of a subdominant scalar field are converted into adiabatic, nearly scale-invariant curvature perturbations after inflation. By analyzing a two-field quadratic potential and deriving the curvature perturbation amplitude in regimes where the curvaton decays before or after dominating the energy density, the authors map the viable parameter space under both prompt and prolonged reheating scenarios. They demonstrate that Gaussian, adiabatic perturbations consistent with observations can be obtained within restricted regions of the four-parameter space {m, M, σ*, Γσ}, and highlight that the model generically predicts a low amplitude for primordial gravitational waves. The work provides a complete constraint set for the simplest curvaton realization and discusses its observational implications and degeneracy with inflationary predictions.

Abstract

We analyze the simplest possible realization of the curvaton scenario, where a nearly scale-invariant spectrum of adiabatic perturbations is generated by conversion of an isocurvature perturbation generated during inflation, rather than the usual inflationary mechanism. We explicitly evaluate all the constraints on the model, under both the assumptions of prompt and delayed reheating, and outline the viable parameter space.

Paper Structure

This paper contains 6 sections, 17 equations, 2 figures.

Table of Contents

  1. Introduction
  2. The simplest curvaton model
  3. Model constraints
  4. The case of prompt reheating
  5. The case of prolonged reheating
  6. Conclusions

Figures (2)

  • Figure 1: Allowed regions of parameter space for $\sigma_*=10^{-8} m_{{\rm Pl}}$ (left panel) and $\sigma_*=10^{-4}m_{{\rm Pl}}$ (right panel). In all cases, the constraint lines are identified with a label on the outside of the allowed region.
  • Figure 2: The parameter space in the case of the curvaton dominating before decay. Models within the triangular region are viable; they have $\sigma_*^2=1.2 \times 10^8\, M^2$, and $\Gamma_\sigma$ may take on any value in the range given by Eq. (\ref{['c2']}).