Quintessence and the Swampland: The numerically controlled regime of moduli space

TL;DR

This paper discusses the theoretical and phenomenological challenges of constructing quintessence models within string theory's moduli space, highlighting the need for specific vacua and the implications for the swampland conjectures.

Contribution

It identifies the conditions for viable quintessence models in string theory and challenges the swampland dS conjecture based on these requirements.

Findings

Viable quintessence requires a non-supersymmetric Minkowski vacuum with an axionic flat direction.

Models consistent with swampland conjectures cannot produce phenomenologically viable quintessence.

Alignment mechanisms in axion models are more promising for dynamical dark energy than hilltop scenarios.

Abstract

We provide a detailed discussion of the main theoretical and phenomenological challenges of quintessence model building in any numerically controlled regime of the moduli space of string theory. We argue that a working quintessence model requires a leading order non-supersymmetric (near) Minkowski vacuum with an axionic flat direction. This axion, when lifted by subdominant non-perturbative effects, could drive hilltop quintessence only for highly tuned initial conditions and a very low inflationary scale. Our analysis has two important implications. Firstly, scenarios which are in agreement with the swampland conjectures, such as those that include runaways, or supersymmetric AdS and Minkowski vacua, cannot give rise to phenomenologically viable quintessence with full computational control. This raises doubts on the validity of the swampland dS conjecture since it would imply a strong tension between quantum gravity and observations. Secondly, if data should prefer dynamical dark energy, axion models based on alignment mechanisms look more promising than highly contrived hilltop scenarios.