Bispectrum from inflation/bouncing Universe in VCDM

TL;DR

This paper investigates the bispectrum in the VCDM modified gravity model during inflation and bouncing phases, showing potential deviations from standard inflationary predictions and compatibility with current observations.

Contribution

It introduces the analysis of non-linear interactions in VCDM, highlighting deviations in non-Gaussianities during different cosmological phases.

Findings

Standard bispectrum results are recovered during slow-roll inflation.

Strong deviations and violation of Maldacena's relation occur when VCDM potential dominates.

Bispectrum in bouncing models remains within observational constraints.

Abstract

We discuss the non-linear interactions within the VCDM model, a type II minimally modified gravity model with the same number of degrees of freedom as in General Relativity but not connected to the latter by field redefinitions. During an inflationary phase in the early universe, if the VCDM potential does not modify the slow-roll behavior of the inflaton field, we recover, up to the leading order, the standard results for the bispectrum in slow-roll inflation. On the other hand, if the VCDM potential becomes dominant, the interactions can strongly deviate and even violate the Maldacena's consistency relation for the local non-Gaussianities. Furthermore, we apply the formalism to the recently introduced bouncing model in VCDM, and show that the bispectrum still respects current observational constraints. Future measurements on non-Gaussianities of the local type should provide the test ground for the model's validity.