Hubble sinks in the low-redshift swampland

Local determinations of the Hubble constant H0 favor a higher value than Planck based on cosmic microwave background and Λ cold dark matter (ΛCDM). Through a model-independent expansion, we show that low redshift (z≲0.7) data comprising baryon acoustic oscillations, cosmic chronometers, and Type Ia supernovae have a preference for quintessence models that lower H0 relative to ΛCDM. 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 H0 from sinking in the string theory swampland.