Hubble Sinks In The Low-Redshift Swampland

Abstract

Local determinations of the Hubble constant $H_0$ favour a higher value than Planck based on CMB and $\hat{I}›$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 $\hat{I}›$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.

4 pages; v2 comments, references added; v3 appendix added on CPL, matches published version