New physics at low redshift cannot be the sole explanation for the H0 tension

Ryan Keeley
UC Merced
Friday, June 3, 2022
2:00 pm
ISEB 1310 [Interdisciplinary Science and Engineering Building]
What has everyone so excited about the H0 tension is the potential for discovering new physics. In particular, the question of new physics explanations for this tension are often divided into whether the new physics plays a role at high redshift or low redshift. In this talk, I will make the case that there can be no low-redshift solution to the H0 tension. To robustly answer this question, I used a very flexible parametrization for the dark energy equation of state, w(z), such that every cosmological distance still allowed by the data exists within this prior volume. To then answer whether there exists a satisfactory solution to the H0 tension within this comprehensive parameterization, I constrained the model using different partitions of the Planck, eBOSS/SDSS DR16 BAO, Pantheon SN and SH0ES H0 datasets. When constrained by just the CMB+H0 datasets, there exists a set of w(z) which yields high H0 values, but these w(z) functions are ruled out by the SN and BAO datasets. In other words, the constraint from CMB+SN+BAO datasets does not allow for high H0 values and converges around w(z)=-1. Thus, the search for a solution to the H0 tension should focus on High-z solutions e.g. early dark energy or features in the primordial power spectrum or interacting neutrinos. Hopefully ACT/SPTPol/CMB-S4 will be able to detect such instances of new physics on their own in order to make a convincing case for a solution to the H0 tension.
Kevork Abazajian