Can small-scale baryon inhomogeneities resolve the Hubble tension? An investigation with ACT DR4

TL;DR

This study tests whether small-scale baryon inhomogeneities can resolve the Hubble tension using ACT DR4 data, finding no evidence for such clumping and confirming the persistent discrepancy in Hubble constant measurements.

Contribution

The paper provides observational constraints on baryon clumping models using ACT DR4 data, showing they cannot resolve the Hubble tension.

Findings

No evidence for baryon clumping in ACT data

Hubble constant remains in tension with SH0ES measurement

Baryon inhomogeneity models are inconsistent with observations

Abstract

Small-scale inhomogeneities in the baryon density around recombination have been proposed as a solution to the tension between local and global determinations of the Hubble constant. These baryon clumping models make distinct predictions for the cosmic microwave background anisotropy power spectra on small angular scales. We use recent data from the Atacama Cosmology Telescope to test these predictions. No evidence for baryon clumping is found, assuming a range of parameterizations for time-independent baryon density probability distribution functions. The inferred Hubble constant remains in significant tension with the SH0ES measurement.