Quantum gravity

Axion

Physics

Dark matter

De Sitter universe

Mathematical physics

String theory

Particle physics

String (physics)

Dark energy

String cosmology

Relationship between string theory and quantum field theory

Cosmology

Theoretical physics

Quantum mechanics

Quintessence

Quantum

Universe

Fortschritte der Physik

De Sitter solutions have been recently conjectured to be incompatible with quantum gravity. In this paper we critically assess the progress and challenges of different mechanisms to obtain de Sitter vacua in string compactifications and compare them to quintessence models. We argue that, despite recent criticisms, de Sitter models reached a level of concreteness and calculational control which has been improving over time. On the other hand, building string models of quintessence appears to be more challenging and requires additional fine-tuning. We discuss the tension between the swampland conjecture and the Higgs potential and find examples which can evade fifth-force bounds even if they seem very hard to realise in string theory. We also comment on the tension with low-redshift data and explore ultra-light axions from string theory as dark energy candidates.

De Sitter vs Quintessence in String Theory