A step in the right direction? Analyzing the Wess Zumino Dark Radiation solution to the Hubble tension

TL;DR

The paper evaluates the Wess Zumino Dark Radiation model's effectiveness in addressing the Hubble tension, analyzing assumptions, data compatibility, and potential for reducing discrepancies in cosmological measurements.

Contribution

It critically assesses the WZDR model's assumptions, confronts it with new data, and explores dark matter interactions to address multiple cosmological tensions.

Findings

WZDR model reduces Planck data tension for low and high multipoles.

Preference for negative curvature remains similar to ΛCDM.

Additional dark matter interactions do not significantly ease the S8 tension.

Abstract

The Wess Zumino Dark Radiation (WZDR) model first proposed in arXiv:2111.00014 shows great promise as a well-motivated simple explanation of the Hubble tension between local and CMB-based measurements. In this work we investigate the assumptions made in the original proposal and confront the model with additional independent data sets. We show that the original assumptions can have an impact on the overall results but are usually well motivated. We further demonstrate that the preference for negative $\Omega_k$ remains at a similar level as for the $\Lambda$CDM model, while the $A_L$ tension is slightly increased. Furthermore, the tension between Planck data for $\ell < 800$ and $\ell \geq 800$ is significantly reduced for the WZDR model. The independent data sets show slightly more permissive bounds on the Hubble parameter, allowing the tension to be further reduced to $2.1 \sigma$ (CMB-independent) or $1.9\sigma$ (ACT+WMAP). However, no combination shows a large preference for the presence of WZDR. We also investigate whether additional dark radiation -- dark matter interactions can help in easing the $S_8$ tension as well. Assuming all of the dark matter to be interacting and a temperature-independent scattering rate, we find that the CMB data are too restrictive on this additional component as to allow a significant decrease in the clustering.