Savior curvatons and large non-Gaussianity

Abstract

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 ns, the tensor-to-scalar ratio r, and the local non-Gaussianity $$ {f}_{\textrm{NL}}^{\left(\textrm{loc}\right)} $$ 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 ns and r observational constraints but can be made viable with a significant contribution from what we call a savior curvaton, a large $$ \left|{f}_{\textrm{NL}}^{\left(\textrm{loc}\right)}\right| $$ 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 ns and r observational constraints, so significant curvaton contribution is forbidden, a large $$ \left|{f}_{\textrm{NL}}^{\left(\textrm{loc}\right)}\right| $$ 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.