Continuous Spectrum on Cosmological Collider

TL;DR

This paper investigates how a massive field with a continuous spectrum influences the inflationary bispectrum, revealing a damping feature in the squeezed limit that could serve as evidence for extra-dimensional physics.

Contribution

It extends the quasi-single field inflation model to include a continuum isocurvaton, analyzing its unique impact on the bispectrum in the squeezed limit.

Findings

Bispectrum amplitude exhibits damping in the deep squeezed limit due to the continuum spectrum.

The model provides a potential observational signature of extra dimensions in inflation.

Continuous spectrum effects differ significantly from discrete cases in inflationary bispectra.

Abstract

We study the effects of a massive field with a continuous spectrum (continuum isocurvaton) on the inflationary bispectrum in the squeezed limit. As a concrete example, we extend the quasi-single field inflation model to include a continuum isocurvaton with a well-motivated spectral density from extra dimensions and focus on a contribution to the bispectrum with a single continuum isocurvaton exchange. In contrast to the usual case without the continuous spectrum, the amplitude of the bispectrum has a damping feature in the deep squeezed limit, which can be strong evidence for the continuous spectrum.