Hubble tension in lepton asymmetric cosmology with an extra radiation

TL;DR

This paper explores how lepton asymmetric cosmology with extra radiation components can alleviate the Hubble tension by fitting cosmological data with additional parameters like neutrino degeneracy and effective neutrino number.

Contribution

It introduces a model with extra radiation and neutrino degeneracy parameters, showing these can reconcile Hubble tension with observational data.

Findings

Hubble tension can be reduced with specific neutrino degeneracy and extra radiation.

Larger $N_{eff}$ is compatible with BBN when neutrino degeneracy is positive.

Best fit parameters suggest $\xi_e \,\simeq 0.04$ and $\,0.3 \lesssim \Delta N_{eff} \lesssim 0.6$.

Abstract

We study the fit of cosmological models with two additional free parameters $N_\mathrm{eff}$ and $\xi_e$ in addition to the parameters of $\Lambda$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 $\xi_e$ 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 $\xi_{e}\simeq 0.04$ and $0.3 \lesssim \Delta N_\mathrm{eff} \lesssim 0.6$.