Inflation in a scale invariant universe

TL;DR

This paper investigates inflation within a scale-invariant gravity framework involving two scalar fields, demonstrating that scale symmetry cancels isocurvature modes and yields predictions consistent with current observations.

Contribution

It introduces a frame-invariant approach to analyze inflation in a scale-invariant two-scalar-field theory, showing the theory simplifies to a single scalar field model after symmetry breaking.

Findings

Isocurvature modes are exactly canceled by scale symmetry.

The theory's predictions align well with current observational data.

In the broken phase, the model reduces to a single scalar field description.

Abstract

A scale-invariant universe can have a period of accelerated expansion at early times: inflation. We use a frame-invariant approach to calculate inflationary observables in a scale invariant theory of gravity involving two scalar fields - the spectral indices, the tensor to scalar ratio, the level of isocurvature modes and non-Gaussianity. We show that scale symmetry leads to an exact cancellation of isocurvature modes and that, in the scale-symmetry broken phase, this theory is well described by a single scalar field theory. We find the predictions of this theory strongly compatible with current observations.