Stringy multifield quintessence and the Swampland

TL;DR

This paper examines string-inspired multifield quintessence models for dark energy, finding that viable cosmological trajectories are hard to realize unless specific initial conditions are assumed, and discusses related Q-ball formation constraints.

Contribution

It investigates the embedding of multifield quintessence in string theory and analyzes the initial conditions necessary for viable late-time cosmic acceleration.

Findings

No compatible trajectories from matter-dominated initial conditions.

Universal trajectories exist with kinetic domination initial conditions.

Q-ball formation constraints impose additional restrictions.

Abstract

We consider quintessence models within 4D effective descriptions of gravity coupled to two scalar fields. These theories are known to give rise to viable models of late-time cosmic acceleration without any need for flat potentials, and so they are potentially in agreement with the dS Swampland conjecture. In this paper we investigate the possibility of consistently embedding such constructions in string theory. We identify situations where the quintessence fields are either closed string universal moduli or non-universal moduli such as blow-up modes. We generically show that no trajectories compatible with today's cosmological parameters exist, if one starts from matter-dominated initial conditions. It is worth remarking that universal trajectories compatible with observations do appear, provided that the starting point at early times is a phase of kinetic domination. However, justifying this choice of initial conditions on solid grounds is far from easy. We conclude by studying Q-ball formation in this class of models and discuss constraints coming from Q-ball safety in all cases analyzed here.