Domestic Corpuscular Inflaton

TL;DR

This paper refines the corpuscular inflation model by analyzing the spectrum of gravitational degrees of freedom in an expanded Starobinsky framework, revealing the nature of scalar and tensor modes during slow-roll inflation.

Contribution

It provides a detailed analysis of the propagating degrees of freedom in corpuscular inflation, clarifying the role of the Einstein-Hilbert term as a perturbation.

Findings

Scalar mode is tachyonic during slow-roll

Tensor mode is transverse and trace-free

Einstein-Hilbert term drives inflation exit

Abstract

The aim of this paper is to provide a more precise description of the paradigm of corpuscular slow-roll inflation, which was previously introduced by Casadio et al. in [1]. Specifically, we start by expanding the Starobinsky theory on a curved background and then infer the number and nature of the propagating degrees of freedom, both in the true inflationary phase and in a quasi-de Sitter approximation. We correctly find that the particle spectrum contains a transverse trace-free mode and a scalar one. The scalar mode displays a tachyonic nature during the slow-roll phase, due to the instability of the system, whereas it acquires the appropriate oscillatory behavior as the background approaches a critical value of the curvature. These results confirm the fact that the Einstein-Hilbert term acts as a perturbation to the quadratic one, and is responsible for driving the early universe out of the inflationary phase, thus realising the inflaton field in terms of pure (corpuscular) gravity.