Too Hot to Handle: Searching for Inflationary Particle Production in Planck Data

TL;DR

This paper searches for inflationary particle production signatures in Planck CMB data, using a novel hotspot detection method, to place bounds on particle-inflaton couplings at energies surpassing previous observational limits.

Contribution

It introduces a matched-filter analysis for detecting inflationary hotspots in CMB data, providing the first constraints on massive particle production during inflation from Planck observations.

Findings

No evidence for inflationary hotspots was found in the data.

The analysis constrains inflaton coupling to massive particles up to energies 100 times the inflationary Hubble scale.

The method is validated on synthetic data and covers about 60% of the sky.

Abstract

Non-adiabatic production of massive particles is a generic feature of many inflationary mechanisms. If sufficiently massive, these particles can leave features in the cosmic microwave background (CMB) that are not well-captured by traditional correlation function analyses. We consider a scenario in which particle production occurs only in a narrow time-interval during inflation, eventually leading to CMB hot- or coldspots with characteristic shapes and sizes. Searching for such features in CMB data is analogous to searching for late-Universe hot- or coldspots, such as those due to the thermal Sunyaev-Zel'dovich (tSZ) effect. Exploiting this data-analysis parallel, we perform a search for particle-production hotspots in the Planck PR4 temperature dataset, which we implement via a matched-filter analysis. Our pipeline is validated on synthetic observations and found to yield unbiased constraints on sufficiently large hotspots across $\approx 60\%$ of the sky. After removing point sources and tSZ clusters, we find no evidence for new physics and place novel bounds on the coupling between the inflaton and massive particles. These bounds are strongest for larger hotspots, produced early in inflation, whilst sensitivity to smaller hotspots is limited by noise and beam effects. Through such methods we can constrain particles with masses $\mathcal{O}(100)$ times larger than the inflationary Hubble scale, which represents possibly the highest energies ever directly probed with observational data.