Cosmological Collider Searches beyond the Hubble Scale with Planck Data

TL;DR

This paper explores the potential of cosmological collider physics to detect heavy particles during inflation using Planck data, introducing new methods to search for non-Gaussian signals beyond the Hubble scale.

Contribution

It develops a theoretical framework for identifying non-Gaussian signatures from heavy particles and performs the first Planck data search for particles heavier than the Hubble scale with a chemical potential mechanism.

Findings

No evidence for NG from particles with mass ~H.

First search for particles heavier than H using Planck data.

A 1.7σ hint of non-zero NG with chemical potential mechanism.

Abstract

Searches for primordial non-Gaussianity (NG) has the potential to not only reveal the physics of cosmic inflation, but also the structure of fundamental interactions at the highest energies. The cosmological collider (CC) physics program exemplifies this possibility and demonstrates how searches for oscillatory NG can lead to mass-spin spectroscopy of extremely heavy states. Adopting an effective field theory approach, we find the class of Feynman diagrams that can give the largest NG mediated by a heavy scalar particle with mass $M\sim H$, the inflationary Hubble scale. We compute the full shape of the NG and perform the first search for this shape using Planck data, finding no evidence for NG. This search loses its sensitivity as $M\gg H$ since quantum vacuum fluctuations cannot efficiently produce such heavier particles. We then focus on a mechanism where a chemical potential excites on-shell scalar particles with mass $M\gg H$. Computing the full shapes, we perform the first CC search for particles parametrically heavier than $H$ using Planck data. For a range of chemical potential $\omega$ and $M$ satisfying $\omega-M \simeq 3H$, we find a global $1.7\sigma$ evidence for non-zero NG, after taking into account the look-elsewhere effect.