Full quantum trispectrum in multifield DBI inflation

Abstract

We compute the leading order connected four-point function of the primordial curvature perturbation coming from the four-point function of the fields in multifield DBI-inflation models. We confirm that the consistency relations in the squeezed limit and in the counter-collinear limit hold as in single-field models thanks to special properties of the DBI action. We also study the momentum dependence of the trispectra coming from the adiabatic, mixed and purely entropic contributions separately and we find that they have different momentum dependence. This means that if the amount of the transfer from the entropy perturbations to the curvature perturbation is significantly large, the trispectrum can distinguish multifield DBI-inflation models from single-field DBI-inflation models. A large amount of transfer ${T}_{\mathcal{R}\mathcal{S}}\ensuremath{\gg}1$ suppresses the tensor-to-scalar ratio $r\ensuremath{\propto}{T}_{\mathcal{R}\mathcal{S}}^{\ensuremath{-}2}$ and the amplitude of the bispectrum ${f}_{\mathrm{NL}}^{\mathrm{equi}}\ensuremath{\propto}{T}_{\mathcal{R}\mathcal{S}}^{\ensuremath{-}2}$ and so it can ease the severe observational constraints on the DBI-inflation model based on string theory. On the other hand, it enhances the amplitude of the trispectrum ${\ensuremath{\tau}}_{\mathrm{NL}}^{\mathrm{equi}}\ensuremath{\propto}{T}_{\mathcal{R}\mathcal{S}}^{2}{f}_{\mathrm{NL}}^{\mathrm{equi}\text{ }2}$ for a given amplitude of the bispectrum.