Stringy multifield quintessence and the Swampland

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.

Automated summary

This study investigates the consistency of embedding quintessence models within gravity coupled to two scalar fields in string theory. The results show difficulties in finding trajectories compatible with cosmological parameters, but universal trajectories may be compatible if the starting point is a phase of kinetic domination. However, justifying the choice of initial conditions remains challenging.