Constraining the bispectrum from bouncing cosmologies with Planck

TL;DR

This paper demonstrates that bouncing cosmological models, which could explain large-scale CMB anomalies through non-Gaussianities, are strongly constrained and largely ruled out by Planck data.

Contribution

It provides the first comprehensive analysis showing that bouncing models with significant non-Gaussianities are incompatible with Planck observations.

Findings

Bouncing models with parameters addressing CMB anomalies are excluded at high significance.

Non-Gaussianities in these models are detectable and inconsistent with Planck data.

Planck data constrains bouncing models more strongly than previously thought.

Abstract

Bouncing models of cosmology, as they arise e.g. in loop quantum cosmology, can be followed by an inflationary phase and generate close-to-scale-invariant fluctuation spectra as observed in the Cosmic Microwave Background (CMB). However, they are typically not Gaussian and also generate a bispectrum. These models can help to mitigate the large-scale anomalies of the CMB by considering substantial non-Gaussianities on very large scales, which decay exponentially on sub-horizon scales. It was therefore thought that this non-Gaussianity would not be visible in observations, which can only probe sub-horizon scales. In this letter we show that bouncing models with parameters such that they can significantly mitigate the large-scale anomalies of the CMB are excluded by the Planck data with high significance of, depending on the specific model, $5.4$, $6.4$ or $14$ standard deviations.