Savior curvatons and large non-Gaussianity

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(NL)((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(NL)((loc))| > 0.05, such that the model is distinguishable from single-field inflation, 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(NL)((loc))| > 0.05 is possible in the exceptional case when the isocurvature fluctuation in the curvaton fluid is much greater than the global curvature fluctuation.