BOSS Constraints on Massive Particles during Inflation: The Cosmological Collider in Action

TL;DR

This paper uses galaxy clustering and CMB data to search for signatures of massive spin-zero particles during inflation, enhancing techniques to connect early universe physics with observable large-scale structures.

Contribution

It introduces improved Cosmological Bootstrap methods and combines perturbation theory with halo models to constrain non-degenerate inflationary particle signatures.

Findings

Constraints on spin-zero particle couplings during inflation

Identification of non-degenerate non-Gaussianity signatures

Enhanced techniques for inflationary spectroscopy

Abstract

Massive particles leave imprints on primordial non-Gaussianity via couplings to the inflaton, even despite their exponential dilution during inflation: practically, the Universe acts as a Cosmological Collider. We present the first dedicated search for spin-zero particles using BOSS redshift-space galaxy power spectrum and bispectrum multipoles, as well as Planck CMB non-Gaussianity data. We demonstrate that some Cosmological Collider models are well approximated by the standard equilateral and orthogonal parametrization; assuming negligible inflaton self-interactions, this facilitates us translating Planck non-Gaussianity constraints into bounds on Collider models. Many models have signatures that are not degenerate with equilateral and orthogonal non-Gaussianity and thus require dedicated searches. Here, we constrain such models using BOSS three-dimensional redshift-space galaxy clustering data, focusing on spin-zero particles in the principal series (i.e. with mass $m\geq 3H/2$) and constraining their couplings to the inflaton at varying speed and mass, marginalizing over the unknown inflaton self-interactions. This is made possible through an improvement in Cosmological Bootstrap techniques and the combination of perturbation theory and halo occupation distribution models for galaxy clustering. Our work sets the standard for inflationary spectroscopy with cosmological observations, providing the ultimate link between physics on the largest and smallest scales.