Shapes of the Cosmological Low-Speed Collider

TL;DR

The paper introduces the cosmological low-speed collider signal, a new method to detect heavy particles during inflation through distinctive resonances in cosmological correlators, especially when the Goldstone boson has a reduced speed of sound.

Contribution

It develops a non-local effective field theory to describe the low-speed collider signal, enabling systematic analysis of massive field effects on cosmological correlators beyond traditional particle production signatures.

Findings

Identifies a new resonance in cosmological correlators indicating heavy particles.

Shows large non-Gaussianities with unique shapes can be generated.

Provides a template for future observational searches.

Abstract

Massive particles produced during inflation leave specific signatures in soft limits of correlation functions of primordial fluctuations. When the Goldstone boson of broken time translations acquires a reduced speed of sound, implying that de Sitter boosts are strongly broken, we introduce a novel discovery channel to detect new physics during inflation, called the cosmological low-speed collider signal. This signal is characterised by a distinctive resonance lying in mildly-soft kinematic configurations of cosmological correlators, indicating the presence of a heavy particle, whose position enables to reconstruct its mass. We show that this resonance can be understood in terms of a non-local single field effective field theory, in which the heavy field becomes effectively non-dynamical. This theory accurately describes the full dynamics of the Goldstone boson and captures all multi-field physical effects distinct from the non-perturbative particle production leading to the conventional cosmological collider signal. As such, this theory provides a systematic and tractable way to study the imprint of massive fields on cosmological correlators. We conduct a thorough study of the low-speed collider phenomenology in the scalar bispectrum, showing that large non-Gaussianities with new shapes can be generated, in particular beyond weak mixing. We also provide a low-speed collider template for future cosmological surveys.