From Inflation to Quintessence: a History of the Universe in String Theory

TL;DR

This paper develops a string theory model that describes the universe's evolution from inflation to dark energy, featuring stabilized moduli and ultra-light axions capable of explaining quintessence and dark matter.

Contribution

It introduces a type IIB string model with stabilized moduli that accounts for the entire cosmic history, including inflation and dark energy, using ultra-light axions and non-perturbative effects.

Findings

The model achieves the observed dark energy scale via poly-instanton effects.

Ultra-light axions can drive quintessence if their decay constants are sufficiently large.

Dark matter can originate from primordial black holes or the QCD axion.

Abstract

We present a type IIB 4D string model with stabilised moduli which is able to describe the history of the universe from inflation to quintessence. The underlying Calabi-Yau volume is controlled by two moduli which are stabilised by perturbative effects. The lighter of them drives Fibre Inflation at a large energy scale. The two associated axions are ultra-light since they are lifted only at the non-perturbative level. The lighter of them can drive quintessence if its decay constant is large enough to prevent quantum diffusion during inflation from ruining the initial conditions. The right dark energy scale can be obtained via a large suppression from poly-instanton effects. The heavier axion gives a negligible contribution to dark matter since it starts oscillating after matter-radiation equality. If instead none of the two axions has a large decay constant, a mild alignment allows the lighter axion to drive quintessence, while the heavier can be at most a few percent of dark matter due to isocurvature and UV bounds. In both cases dark matter can also come from either primordial black holes or the QCD axion.