Hubble tension in lepton asymmetric cosmology with an extra radiation

Abstract

We study the fit of cosmological models with two additional free parameters $N_{\mathrm{eff}}$ and $\hat{I}{¾}_e$ in addition to the parameters of $\hat{I}›$CDM. We introduce extra radiation components such as hot axions or sterile neutrinos in addition to the energy density of neutrinos with large neutrino degeneracy. Then, a larger $N_{\mathrm{eff}}$ is allowed without spoiling Big Bang Nucleosynthesis (BBN), as positive neutrino degeneracy $\hat{I}{¾}_e$ could improve BBN fit. By analysing the data from Planck, baryon acoustic oscillation (BAO), BBN and type-Ia supernovae (SNeIa), it can be seen that the Hubble tension can be ameliorated for $\hat{I}{¾}_e\simeq 0.04$ and $0.3\lesssim \hat{I}”N_{\mathrm{eff}}\lesssim 0.6$.

12 pages 3 figures