Shapes of the cosmological low-speed collider

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.

On the importance of heavy fields in pseudo-scalar inflation

“…The distinctive sharpness of the non-Gaussianity can, in principle, be distinguished from that observed in single axion inflation. Upon identifying specific models, the effects of heavy fields can potentially be detected in cosmological colliders in the future [52,. One particularly intriguing model is rapid-turn inflation, characterized by an exceptionally rapid turning rate of the classical trajectory, resulting in a reduction of the speed of sound (3.7) (c 2 s < 0).…”

“…The small sound speed can be also achieved without any heavy fields[51,52] 2. The actual integrated out d.o.f are the high-frequency modes in ζ and F[44].…”

Decoherence out of fire: purity loss in expanding and contracting universes

“…Lastly, our work highlights that the near-decoupling limit in cosmology can have considerably richer behaviour than its flat space counterparts. It may therefore be interesting to more deeply explore the relationship between Open and Wilsonian EFTs in cosmological systems, and whether there exist useful non-unitary (and perhaps non-local [168][169][170]) effective descriptions for more simply (and agnostically from a model-building point of view) studying such a limit. We leave this for future work.…”

CosmoFlow: Python package for cosmological correlators

“…The corresponding shape is neither faithfully represented by the standard local shape [54][55][56][57] nor the equilateral one [53,58]. Indeed, the parameters we used, c s = 0.05, m/H = 2 and ρ/H = 0.1, fall within the low-speed collider regime, in which the signal is characterised by a resonance in mildly squeezed configurations, see [59,60] for more details. Our numerical method is perfectly capable of capturing this effect.…”