Squeezed bispectrum from multi-field inflation with curved field space metric

TL;DR

This paper analyzes how a curved field-space metric in multi-field inflation models affects the squeezed bispectrum, revealing significant modifications that could impact observable signatures in galaxy surveys.

Contribution

It provides analytic expressions for the reduced bispectrum considering curved field-space metrics, highlighting their impact on inflationary non-Gaussianities.

Findings

Curved field-space metric can significantly alter the amplitude and shape of the bispectrum.

The spectral index of halo bias can be 2-4 times larger due to curvature effects.

Observable imprints in galaxy surveys could reveal the influence of field-space curvature.

Abstract

We investigate influences of the curved field-space metric of multi-field inflationary models on the squeezed bispectrum. The reduced bispectrum in squeezed limit is computed using the {\delta}N formalism. The calculation is performed under the slow-roll approximation and assumption that field derivative of the field-space metric is sufficiently small such that the contributions from Riemann tensor of the field-space can be approximately ignored. Based on these approximations, We compute the analytic expressions for the reduced bispectrum in squeezed limit, and find that, for such a nearly flat field-space metric, the field dependence of the metric can significantly alter both amplitude and shape of the reduced bispectrum. The reduced bispectrum from this nearly flat field-space metric can lead to spectral index of the halo bias which amplitude is 2 -- 4 times larger than that from the flat field-space model. This modification of the spectral index of the halo bias due to the curved field-space metric could leave observable imprints in future galaxy surveys.