The Impact of Non-Gaussian Primordial Tails on Cosmological Observables

Abstract

Whilst current observational evidence favors a close-to-Gaussian spectrum of primordial perturbations, there exist many models of the early Universe that predict this distribution to have exponentially enhanced or suppressed tails. In this work, we generate realizations of the primordial potential with non-Gaussian tails via a phenomenological model; these are then evolved numerically to obtain maps of the cosmic microwave background (CMB) and large-scale structure (LSS). In the CMB maps, our added non-Gaussianity manifests as a localized enhancement of hot and cold spots, which would be expected to contribute to $N$-point functions up to large $N$. Such models are indirectly constrained by \textit{Planck} trispectrum bounds, which restrict the changes in the temperature fluctuations to $O(10\mu\mathrm{K})$. In the late-time Universe, we find that tailed cosmologies lead to a halo mass function enhanced at high masses, as expected. Furthermore, significant scale-dependent bias in the halo-halo and halo-matter power spectrum is also sourced, which arises from the squeezed limit of large $N$-point functions that are implicitly generated through the enhancement of the tails. These results underscore that a detection of scale-dependent bias alone cannot be used to rule out single field inflation, but can be used together with other statistics to probe a wide range of primordial processes.