Abstract
We discuss the cosmological implications of the string swampland conjectures for late-time cosmology, and test them against a wide range of state of the art cosmological observations. The refined de Sitter conjecture constrains either the minimal slope or the curvature of the scalar potential, and depends on two dimensionless constants. For constants of size one or larger, tension exists between observations, especially the Hubble constant, and the slope and curvature conjectures at a level of 4.5 sigma and 2.3 sigma, respectively. Smaller values of the constants are permitted by observations, and we determine upper bounds at varying confidence levels. We also derive and constrain the relationship between cosmological observables and the scalar field excursion during the acceleration epoch, thereby testing the distance conjecture.
Highlights
There is currently a vibrant debate in string theory about whether space-times with positive cosmological constant are compatible with quantum gravity
To highlight the power of distance-redshift measurements in testing these conjectures we consider the Pantheon Supernovae sample [53], that we denote as the SN dataset, and distance-ladder measurement of the Hubble constant from [54], that we indicate as the H0 dataset
In this paper we studied the cosmological implications of the refined de Sitter (C1) and distance (C2) swampland conjectures that have been proposed in literature
Summary
There is currently a vibrant debate in string theory about whether space-times with positive cosmological constant are compatible with quantum gravity. What we know today is that four-dimensional or higher de Sitter space-times are ruled out as solutions of the D 1⁄4 10 or D 1⁄4 11 fundamental supergravity theories [2,3], and as solutions of type I/heterotic supergravity together with the leading higher derivative couplings [4,5], and as solutions of heterotic world sheet conformal field theory [6]. This is compelling evidence that de Sitter space-time cannot be found in regions of parametric control in string theory. This same conclusion can be argued from entropy considerations in regimes of weak coupling in string theory [7]
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