Primordial statistical anisotropy generated at the end of inflation

TL;DR

This paper proposes a new inflationary mechanism involving a vector field with a non-minimal kinetic term that induces statistical anisotropy in primordial curvature perturbations, potentially observable in the bispectrum.

Contribution

It introduces a novel hybrid inflation model where a vector field causes anisotropic features in primordial fluctuations, especially affecting the bispectrum without necessarily impacting the power spectrum.

Findings

Explicit formula for statistical anisotropy in the power spectrum and bispectrum.

Statistical anisotropy can manifest in the bispectrum even if absent in the power spectrum.

The anisotropy introduces shape dependence in the bispectrum.

Abstract

We present a new mechanism for generating primordial statistical anisotropy of curvature perturbations. We introduce a vector field which has a non-minimal kinetic term and couples with a waterfall field in hybrid inflation model. In such a system, the vector field gives fluctuations of the end of inflation and hence induces a subcomponent of curvature perturbations. Since the vector has a preferred direction, the statistical anisotropy could appear in the fluctuations. We present the explicit formula for the statistical anisotropy in the primordial power spectrum and the bispectrum of curvature perturbations. Interestingly, there is the possibility that the statistical anisotropy does not appear in the power spectrum but does appear in the bispectrum. We also find that the statistical anisotropy provides the shape dependence to the bispectrum.