Inflation without an Inflaton

TL;DR

This paper introduces a new inflationary model where scalar perturbations are generated without an inflaton field, relying on quantum vacuum effects in a de Sitter space to produce the observed large-scale structure.

Contribution

It presents a novel inflationary scenario driven by de Sitter space with scalar fluctuations arising from tensor effects, eliminating the need for an inflaton field.

Findings

Scalar power spectrum is consistent with near scale-invariance.

Conditions for significant scalar perturbations are derived.

A natural transition mechanism to radiation domination is identified.

Abstract

We propose a novel scenario in which scalar perturbations, that seed the large scale structure of the Universe, are generated without relying on a scalar field (the inflaton). In this framework, inflation is driven by a de Sitter space-time (dS), where tensor metric fluctuations (i.e., gravitational waves) naturally arise from quantum vacuum oscillations, and scalar fluctuations are generated via second-order tensor effects. We compute the power spectrum of such scalar fluctuations and show it to be consistent with near scale-invariance. We derive the necessary conditions under which scalar perturbations become significant and much larger than the tensor modes, and we identify a natural mechanism to end inflation via a transition to a radiation-dominated phase. Our proposed mechanism could remove the need for a model-dependent scenario: the choice of a scalar field, as the inflaton, to drive inflation.