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

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.