Is there an early Universe solution to Hubble tension?

We consider a low redshift ($z<0.7$) cosmological data set comprising megamasers, cosmic chronometers, type Ia supernovae and baryon acoustic oscillations, which we bin according to their redshift. For each bin, we read the value of $H_0$ by fitting directly to the flat $\mathrm{\Lambda }\mathrm{CDM}$ model. Doing so, we find that $H_0$ descends with redshift, allowing one to fit a line with a nonzero slope of statistical significance $2.1\sigma$. Our analysis rests on the use of cosmic chronometers to break a degeneracy in baryon acoustic oscillations data and it will be imperative to revisit this feature as data improves. Nevertheless, our results provide the first independent indication of the descending trend reported by the H0LiCOW Collaboration. If substantiated going forward, early Universe solutions to the Hubble tension will struggle explaining this trend.

Figure 1

Overlapping probability distribution functions for each bin plotted alongside the overall constraint.

Figure 2

The best-fit line against the binned data. The line is $2.1\sigma$ removed from the flat line null hypothesis.