Bispectrum from five-dimensional inflation

TL;DR

This paper explores five-dimensional inflation, demonstrating how it affects primordial scalar perturbations' bispectrum, revealing deviations from four-dimensional models and potential observational signatures.

Contribution

It provides the first computation of the bispectrum in 5D inflation, highlighting differences from 4D cases and the impact of broken conformal invariance.

Findings

Bispectrum differs from 4D case at all angles

Enhanced signal in the squeezed limit

Potential observational signatures of 5D inflation

Abstract

It was proposed that five-dimensional (5D) inflation can blow up the size of a compact dimension from the 5D Planck length to the micron size, as required by the dark dimension proposal, relating the weakness of the actual gravitational force to the size of the observable universe. Moreover, it was shown that 5D inflation can generate the (approximate) flat power spectrum of primordial density fluctuations consistent with present observations. Here we compute the bispectrum of primordial scalar perturbations and show that unlike the power spectrum, it differs from the four-dimensional case at all angular distances, due to the fact that in contrast to global dilatations, invariance under special conformal transformations is not restored at late times. Moreover there is an additional enhancement in the squeezed limit.