Non-minimally coupled curvaton

Abstract

We investigate two-field inflationary models in which scalar cosmological pertubations are generated viaa spectator field nonminimallycoupled to gravity, with the particular emphasis oncurvaton scenarios.The principal advantage of these models is in the possibility to tunethe spectator spectral index via the nonminimal coupling.Our models naturally yield red spectrum of the adiabatic perturbation demanded by observations.We study how the nonminimal coupling affects the spectrum of the curvature perturbationgenerated in the curvaton scenarios. In particular we find that for small, negative nonminimal couplingsthe spectral index gets a contribution that is negative and linear in the nonminimal coupling.Since in this way the curvature spectrum becomes redder, some of curvaton scenarios canbe saved, which would otherwise be ruled out.In the power law inflation we find that a large nonminimal coupling is excluded sinceit gives the principal slow-roll parameter that is of the order of unity.Finally, we point out that nonminimal coupling can affectthe postinflationary growth of the spectator perturbation,and in this way the effectiveness of the curvaton mechanism.