Hubble tension in lepton asymmetric cosmology with an extra radiation
Osamu Seto, Yo Toda
Abstract
We study the fit of cosmological models with two additional free parameters ${N}_{\mathrm{eff}}$ and ${\ensuremath{\xi}}_{e}$ in addition to the parameters of $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$. 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 ${\ensuremath{\xi}}_{e}$ 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 ${\ensuremath{\xi}}_{e}\ensuremath{\simeq}0.04$ and $0.3\ensuremath{\lesssim}\mathrm{\ensuremath{\Delta}}{N}_{\mathrm{eff}}\ensuremath{\lesssim}0.6$.