The landscape, the swampland and the era of precision cosmology

TL;DR

This paper reviews advanced string theory models related to de Sitter space and argues against certain conjectures, showing that alternative dark energy models are inconsistent with cosmological data at high confidence.

Contribution

It critically examines conjectures about the non-existence of de Sitter space in string theory and evaluates alternative dark energy models against observational constraints.

Findings

Conjectures about de Sitter space are problematic and not well motivated.

Alternative models ignoring vacuum stabilization are ruled out by cosmological data at 3σ level.

The review supports the viability of certain string theory constructions in cosmology.

Abstract

We review the advanced version of the KKLT construction and pure $d=4$ de Sitter supergravity, involving a nilpotent multiplet, with regard to various conjectures that de Sitter state cannot exist in string theory. We explain why we consider these conjectures problematic and not well motivated, and why the recently proposed alternative string theory models of dark energy, ignoring vacuum stabilization, are ruled out by cosmological observations at least at the $3\sigma$ level, i.e. with more than $99.7\%$ confidence.