Early Dark Energy in Type IIB String Theory

TL;DR

This paper constructs models of Early Dark Energy within type IIB string theory, identifying the EDE field as axions and demonstrating how to naturally achieve the required energy scales and decay constants without fine-tuning, addressing the Hubble Tension.

Contribution

It develops explicit realizations of EDE in type IIB string theory with stabilized moduli, analyzing the conditions under which the EDE parameters can be naturally obtained.

Findings

EDE can be realized with axions in type IIB string theory.

Natural hierarchy of energy scales achieved without tuning for certain models.

C2 axions in LVS with non-perturbative effects are promising EDE candidates.

Abstract

Early Dark Energy (EDE) is a promising model to resolve the Hubble Tension, that, informed by Cosmic Microwave Background data, features a generalization of the potential energy usually associated with axion-like particles. We develop realizations of EDE in type IIB string theory with the EDE field identified as either a $C_4$ or $C_2$ axion and with full closed string moduli stabilization within the framework of either KKLT or the Large Volume Scenario. We explain how to achieve a natural hierarchy between the EDE energy scale and that of the other fields within a controlled effective field theory. We argue that the data-driven EDE energy scale and decay constant can be achieved without any tuning of the microscopic parameters for EDE fields that violate the weak gravity conjecture, while for states that respect the conjecture it is necessary to introduce a fine-tuning. This singles out as the most promising EDE candidates, amongst several working models, the $C_2$ axions in LVS with 3 non-perturbative corrections to the superpotential generated by gaugino condensation on D7-branes with non-zero world-volume fluxes.