# Swampland Conjectures and Late-Time Cosmology

## TL;DR

This paper tests string swampland conjectures against cosmological data, finding tensions with observations for certain parameter values and providing bounds that inform the viability of these conjectures in late-time cosmology.

## Contribution

It provides the first comprehensive observational constraints on the refined de Sitter and distance swampland conjectures in the context of late-time cosmology.

## Key findings

- Tensions at 4.5 sigma with the Hubble constant for large conjecture constants.
- Allowed smaller constants are consistent with current observations.
- Constraints on scalar field excursions during cosmic acceleration.

## 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.