Constraining the Bispectrum from Bouncing Cosmologies with Planck

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 subhorizon scales. It was therefore thought that this non-Gaussianity would not be visible in observations, which can only probe subhorizon scales. 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.