Hubble Sinks In The Low-Redshift Swampland

TL;DR

This paper investigates low-redshift cosmological data and finds a preference for Quintessence models that lower the Hubble constant $H_0$, challenging the standard $ ext{Lambda}$CDM model and suggesting new physics may be needed.

Contribution

It provides a model-independent analysis showing low-redshift data favors Quintessence over $ ext{Lambda}$CDM in reducing $H_0$, and examines the impact of dark matter coupling.

Findings

Low-redshift data prefers Quintessence models that lower $H_0$.

Exponential dark matter coupling does not change this preference.

Possibility remains that early-universe coupling could reconcile $H_0$ with string theory constraints.

Abstract

Local determinations of the Hubble constant $H_0$ favour a higher value than Planck based on CMB and $\Lambda$CDM. Through a model-independent expansion, we show that low redshift ($z \lesssim 0.7$) data comprising baryon acoustic oscillations (BAO), cosmic chronometers and Type Ia supernovae has a preference for Quintessence models that lower $H_0$ relative to $\Lambda$CDM. In addition, we confirm that an exponential coupling to dark matter cannot alter this conclusion in the same redshift range. Our results leave open the possibility that a coupling in the matter-dominated epoch, potentially even in the dark ages, may yet save $H_0$ from sinking in the string theory Swampland.