The Landscape, the Swampland and the Era of Precision 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 3σ level, i.e. with more than 99.7% confidence.

Cosmological perturbations and dynamical analysis for interacting quintessence

“…In this situation, we would have U m = − 1 4 1 ± 25 − 72 λ 2 , which is real for λ > 6 √ 2 5 . This value for the parameter λ was excluded by cosmological observations more than one decade ago [97,101], being λ > 1 ruled out by at least the 3σ level [102]. Without cosmological perturbations the fixed points (c) might represent a DE-dominated Universe, although the match between the coupling constant in this case and the points (a) is difficult.…”

H0 tension and the string swampland

“…IV. Before proceeding, we note that other ideas relating cosmological observations to the swampland conjectures have been presented in [71][72][73][74][75][76][77][78][79].…”

Higher Structures in M‐Theory

“…This lack of a proper formulation of non‐perturbative string theory is problematic as is witnessed, for instance, in recent debates about the existence or non‐existence of de Sitter vacua in string theory …”

“…recent debates about the existence or non-existence of de Sitter vacua in string theory. [5][6][7] A key issue in formulating M-theory is that its underlying principles have remained unclear. If available hints are anything to go by, M-theory is not simply going to be defined by a Lagrangian, nor a scattering matrix, nor any other traditional structure of quantum physics.…”