Observational signatures of anisotropic inflationary models

TL;DR

This paper investigates how anisotropic inflationary models with vector or two-form couplings affect observable signatures like gravitational waves and non-Gaussianities, providing constraints based on recent Planck data.

Contribution

It compares observational signatures of vector and two-form anisotropic inflation models and derives constraints from Planck data, highlighting differences in scalar-tensor correlations and non-Gaussianities.

Findings

Anisotropic models suppress tensor-to-scalar ratio r.

Scalar spectral index n_s is reduced in both models.

Two-form model shows no scalar-tensor cross correlation.

Abstract

We study observational signatures of two classes of anisotropic inflationary models in which an inflaton field couples to (i) a vector kinetic term F_{mu nu}F^{mu nu} and (ii) a two-form kinetic term H_{mu nu lambda}H^{mu nu lambda}. We compute the corrections from the anisotropic sources to the power spectrum of gravitational waves as well as the two-point cross correlation between scalar and tensor perturbations. The signs of the anisotropic parameter g_* are different depending on the vector and the two-form models, but the statistical anisotropies generally lead to a suppressed tensor-to-scalar ratio r and a smaller scalar spectral index n_s in both models. In the light of the recent Planck bounds of n_s and r, we place observational constraints on several different inflaton potentials such as those in chaotic and natural inflation in the presence of anisotropic interactions. In the two-form model we also find that there is no cross correlation between scalar and tensor perturbations, while in the vector model the cross correlation does not vanish. The non-linear estimator f_{NL} of scalar non-Gaussianities in the two-form model is generally smaller than that in the vector model for the same orders of |g_*|, so that the former is easier to be compatible with observational bounds of non-Gaussianities than the latter.