de Sitter Swampland, H0 tension & observation

Abstract

Realising de Sitter vacua in string theory is challenging. For this reason it has been conjectured that de Sitter vacua inhabit the Swampland of inconsistent low-energy effective theories coupled to gravity. Since de Sitter is an attractor for ΛCDM, the conjecture calls ΛCDM into question. Reality appears sympathetic to this idea as local measurements of the Hubble constant H0 are also at odds with ΛCDM analysis of Planck data. This tension suggests that the de Sitter state is unstable, thereby implying a turning point in the Hubble parameter. We present a model relieving this tension, which predicts a turning at small positive redshift z⁎ that is dictated by present-day matter density ωm. This feature is easily identified by homogeneous surveys covering redshifts z≤0.1. We comment on the implications for the Swampland program.