Hubble sinks in the low-redshift swampland

Local determinations of the Hubble constant H-0 favor a higher value than Planck based on cosmic microwave background and Lambda cold dark matter (Lambda CDM). Through a model-independent expansion, we show that low redshift (z less than or similar to 0.7) data comprising baryon acoustic oscillations, cosmic chronometers, and Type Ia supernovae have 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.

Automated summary

Local determinations of the Hubble constant H-0 based on low redshift data favor quintessence models that lower H-0 relative to Lambda CDM. Additionally, results show that an exponential coupling to dark matter cannot alter this conclusion in the same redshift range. This leaves 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.