Dark Energy as a Post-Inflation Effect in Quadratic Gravity

TL;DR

This paper proposes that Dark Energy may be explained by a Quadratic Gravity model that accounts for cosmic acceleration without dark energy or a cosmological constant, differing from Einstein's gravity especially in later eras.

Contribution

It demonstrates analytically and numerically that Quadratic Gravity can explain cosmic acceleration as a post-inflation effect, providing a novel alternative to dark energy models.

Findings

Quadratic Gravity triggers sufficient inflation without negative pressure matter.

The model predicts a non-shrinking Hubble horizon during radiation and matter eras.

All Einstein metrics are solutions, making classic tests of Einstein's gravity inconclusive for falsification.

Abstract

We analytically and numerically show that the acceleration of the cosmic expansion could be explained by a Quadratic Gravity model which is known to be able to trigger sufficient inflation, with neither negative pressure matter nor cosmological constant. Furthermore, we exactly show that this model differs greatly from Einstein's gravity in radiation and matter dominant era, giving a non-shrinking Hubble horizon and a smooth expansion history of the universe. Accordingly, it suggests that the Dark Energy could possibly be a post-inflation effect in Quadratic Gravity. We also show that this model admits all Einstein metrics as its solutions. Consequently, classic tests of Einstein's Gravity cannot falsify this model.