de Sitter Swampland, $H_0$ tension & observation

TL;DR

This paper explores the connection between de Sitter vacua in string theory, the Swampland conjecture, and the Hubble tension, proposing a model that predicts a turning point in the Hubble parameter at low redshift, potentially resolving the tension.

Contribution

It introduces a model that links the Swampland conjecture to observable cosmological features, specifically addressing the Hubble tension with a testable prediction.

Findings

Predicts a turning point in the Hubble parameter at low redshift z*

Relates the turning point to present-day matter density ω_m

Suggests observational tests via homogeneous surveys at z ≤ 0.1

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 $\Lambda$CDM, the conjecture calls $\Lambda$CDM into question. Reality appears sympathetic to this idea as local measurements of the Hubble constant $H_0$ are also at odds with $\Lambda$CDM 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 $\omega_m$. This feature is easily identified by homogeneous surveys covering redshifts $z \leq 0.1$. We comment on the implications for the Swampland program.