A new mechanism of realizing inflationary universe with recourse to backreaction of quantized free fields -- Inflation without inflaton --

TL;DR

This paper proposes a mechanism for inflation driven by the backreaction of quantized matter fields, eliminating the need for an inflaton field, and demonstrates a self-consistent solution leading to a de Sitter expansion followed by contraction.

Contribution

It introduces a novel inflationary model based on quantum backreaction effects of free scalar fields, providing a self-consistent framework without inflaton fields.

Findings

Universe undergoes de Sitter-like expansion with over 60 e-folds

Hubble parameter decreases rapidly to zero after inflation

Backreaction of quantized fields can drive inflation without an inflaton

Abstract

It is shown that the inflationary era in early universe is realized due to the effect of backreaction of quantized matter fields. In fact we start by quantizing a free scalar field in the Friedmann-Robertson-Walker space-time, and the field is fluctuating quantum mechanically around the bottom of the mass potential. We then obtain the vacuum expectation value of the energy density of the scalar field as a functional of the scale factor $a(t)$ of the universe. By plugging it into the Einstein equation, a self-consistent equation is established in which the matter fields determine the time evolution of the universe. We solve this equation by setting few conditions and find the following solution: the universe expands \`{a} la de Sitter with e-folding number $\gtrsim 60$ and then it turns to shrink with a decreasing Hubble parameter $H(t)$ which rapidly goes to zero.