Missing Scalars at the Cosmological Collider

TL;DR

This paper investigates how missing scalar fields during inflation can influence primordial perturbations, especially by distorting oscillatory features in the bispectrum, providing a way to distinguish different mass origins.

Contribution

It introduces the concept of missing scalars at the cosmological collider and analyzes their observable effects on the bispectrum, particularly the distortion of oscillatory signals.

Findings

Missing scalars can distort the oscillatory features in the squeezed bispectrum.

Distortions help differentiate between thermal and intrinsic mass origins.

Potential observational signals for missing scalars in primordial perturbations.

Abstract

Light scalar fields typically develop spatially varying backgrounds during inflation. Very often they do not directly affect the density perturbations, but interact with other fields that do leave nontrivial signals in primordial perturbations. In this sense they become "missing scalars" at the cosmological collider. We study potentially observable signals of these missing scalars, focusing on a special example where a missing scalar distorts the usual oscillatory features in the squeezed bispectrum. The distortion is also a useful signal distinguishing the de Sitter background induced thermal mass from a constant intrinsic mass.