Savior Curvatons and Large non-Gaussianity

TL;DR

This paper investigates how savior curvatons with quadratic potentials can produce large local non-Gaussianity in the CMB, especially when inflation models are marginal or already constrained.

Contribution

It systematically explores the observable effects of quadratic curvatons, highlighting conditions under which large non-Gaussianity arises in various inflation scenarios.

Findings

Large $f_{NL}^{(loc)}$ is inevitable when inflation models are made viable by savior curvatons.

Significant curvaton contribution can produce large non-Gaussianity even if inflation models already satisfy observational constraints.

Exceptional cases with dominant isocurvature fluctuations can lead to large $f_{NL}^{(loc)})$ in otherwise constrained models.

Abstract

Curvatons are light (compared to the Hubble scale during inflation) spectator fields during inflation that potentially contribute to adiabatic curvature perturbations post-inflation. They can alter CMB observables such as the spectral index $n_s$, the tensor-to-scalar ratio $r$, and the local non-Gaussianity $\;f_{\rm NL}^{\rm (loc)}$. We systematically explore the observable space of a curvaton with a quadratic potential. We find that when the underlying inflation model does not satisfy the $n_s$ and $r$ observational constraints but can be made viable with a significant contribution from what we call a savior curvaton, a large $\;f_{\rm NL}^{\rm (loc)}$ is inevitable. On the other hand, when the underlying inflation model already satisfies the $n_s$ and $r$ observational constraints, so significant curvaton contribution is forbidden, a large $\;f_{\rm NL}^{\rm (loc)}$ is possible in the exceptional case when the isocurvature fluctuation in the curvaton fluid is much greater than the global curvature fluctuation.