Abstract
In this paper, we show how the structure of the landscape potential of the primordial Universe may be probed through the properties of the primordial density perturbations responsible for the origin of the cosmic microwave background anisotropies and the large-scale structure of our Universe. Isocurvature fields -fields orthogonal to the inflationary trajectory- may have fluctuated across the barriers separating local minima of the landscape potential during inflation. We analyze how this process could have impacted the evolution of the primordial curvature perturbations. If the typical distance separating consecutive minima of the landscape potential and the height of the potential barriers are smaller than the Hubble expansion rate parametrizing inflation, the probability distribution function of isocurvature fields becomes non-Gaussian due to the appearance of bumps and dips associated to the structure of the potential. We show that this non-Gaussianity can be transferred to the statistics of primordial curvature perturbations if the isocurvature fields are coupled to the curvature perturbations. The type of non-Gaussian structure that emerges in the distribution of curvature perturbations cannot be fully probed with the standard methods of polyspectra; instead, the probability distribution function is needed. The latter is obtained by summing all the $n$-point correlation functions. To substantiate our claims, we offer a concrete model consisting of an axionlike isocurvature perturbation with a sinusoidal potential and a linear derivative coupling between the isocurvature and curvature fields. In this model, the probability distribution function of the curvature perturbations consists of a Gaussian function with small superimposed oscillations reflecting the isocurvature axion potential.
Highlights
The search for primordial non-Gaussianity (NG) has been guided by our ability to make predictions within the inflationary paradigm [1,2,3,4,5]
We show that this non-Gaussianity can be transferred to the statistics of primordial curvature perturbations if the isocurvature fields are coupled to the curvature perturbations
We extend this mechanism [involving the derivative coupling of Eq (1)] and show that the probability distribution function (PDF) of primordial curvature perturbations may inherit a novel class of non-Gaussianity
Summary
The search for primordial non-Gaussianity (NG) has been guided by our ability to make predictions within the inflationary paradigm [1,2,3,4,5]. We extend this mechanism [involving the derivative coupling of Eq (1)] and show that the probability distribution function (PDF) of primordial curvature perturbations may inherit a novel class of non-Gaussianity. It relies on the existence of an isocurvature field ψ that acquires non-Gaussian statistics through its own selfinteractions [78], which are transferred to curvature perturbations on superhorizon scales.
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