The inflating curvaton

TL;DR

This paper explores a novel inflationary scenario where the curvaton field drives a brief inflation phase before oscillating, offering solutions to the eta problem and making testable predictions for spectral index and non-Gaussianity.

Contribution

It introduces a new curvaton-driven inflation model that addresses the eta problem using string axions and predicts observable signatures for upcoming experiments.

Findings

Spectral index n can be explained with V∝φ^p, p=1 or 2.

Predicted running of the spectral index n' ≈ 0.0026 or 0.0013.

Non-Gaussianity parameter f_NL ≈ -1 may be detectable.

Abstract

The primordial curvature perturbation \zeta may be generated by some curvaton field \sigma, which is negligible during inflation and has more or less negligible interactions until it decays. In the current scenario, the curvaton starts to oscillate while its energy density \rho_\sigma is negligible. We explore the opposite scenario, in which \rho_\sigma drives a few e-folds of inflation before the oscillation begins. In this scenario for generating \zeta it is exceptionally easy to solve the \eta problem; one just has to make the curvaton a string axion, with anomaly-mediated susy breaking which may soon be tested at the LHC. The observed spectral index n can be obtained with a potential V\propto \phi^p for the first inflation; p=1 or 2 is allowed by the current uncertainty in n but the improvement in accuracy promised by Planck may rule out p=1. The predictions include (i) running n'\simeq 0.0026 (0.0013) for p=1 (2) that will probably be observed, (ii) non-gaussianity parameter f_NL \sim -1 that may be observed, (iii) tensor fraction r is probably too small to ever observed.