Testing the coupling of dark radiations in light of the Hubble tension

TL;DR

This paper investigates how self-interacting dark radiation could influence the Hubble tension, showing that it can raise the Hubble constant but faces constraints when combined with free-streaming dark radiation, with future experiments promising precise measurements.

Contribution

It introduces a detailed analysis of self-interacting dark radiation's role in resolving the Hubble tension, including scenarios with mixed dark radiation types and forecasts for future observational constraints.

Findings

SIdr alone can increase H0 to about 70.1 km/s/Mpc.

Including FSdr disfavors significant SIdr presence, with N_{si} \u2248 0.37.

Future experiments could measure N_{si} with 7.64cccc sigma significance.

Abstract

We are studying the effects of Self-Interacting dark radiation (SIdr) on the evolution of the universe. Our main focus is on the cosmic microwave background (CMB) and how SIdr could potentially help resolve the Hubble tension. We are looking into different scenarios by mixing SIdr with Free-Streaming dark radiation (FSdr) or not to determine whether SIdr can indeed contribute to solving the Hubble tension. We find that SIdr alone can increase the Hubble constant ($H_0$) to $70.1_{-1.6}^{+1.3}, \text{km/s/Mpc}$ with a value of $N_{\rm eff}=3.27_{-0.31}^{+0.23}$. However, including \lzy{FSdr} disfavors the existence of SIdr $\tilde N_{\rm si}\approx0.37$. Even though the Hubble constant is increased compared to the predicted value, it entails $N_{\rm eff}=3.52\pm0.25$. Finally, we implement the Fisher method for future experiments and a $7.64\sigma$ measurement of $\tilde N_{\rm si}$ will be obtained when combing data from Planck, AliCPT, and CMB-S4.