Neutrinophilic $\mathbf{\Lambda}$CDM Extension for EMPRESS, DESI and Hubble Tension

TL;DR

This paper proposes an extension to the $ ext{Lambda}$CDM cosmological model involving neutrino asymmetry and additional neutrino contributions, which can simultaneously address recent observational tensions including the Hubble constant discrepancy.

Contribution

It introduces a neutrinophilic $ ext{Lambda}$CDM model with specific neutrino parameters, providing state-of-the-art constraints and demonstrating its effectiveness in alleviating the Hubble tension.

Findings

Neutrino asymmetry $\xi_{ u} = 0.056 \\pm 0.017$ is favored.

Additional neutrino contribution $\\delta N_{\rm eff} = 0.41 \\pm 0.16$ improves model fit.

Hubble tension is reduced to $2.2\sigma$ in this model.

Abstract

A number of recent cosmological observations have indicated the presence of new physics beyond the $\mathbf{\Lambda}$CDM model. Combining observations from EMPRESS on helium abundance and DESI on baryon acoustic oscillations with Hubble tension, we show that all of them can be explained concurrently with a extension of the $\mathbf{\Lambda}$CDM model with primordial neutrino asymmetry $\xi_{\nu}$ and additional contribution to the effective number of neutrinos $\delta N_{\rm eff}$. Based on the accurate treatments of neutrino decoupling and BBN processes, we present state-of-the-art constraints on neutrino asymmetry for the fixed or varying $N_{\rm eff}$. Comparing different extensions of the $\mathbf{\Lambda}$CDM model, we show that the neutrinophilic $\mathbf{\Lambda}$CDM extension with $\xi_{\nu} = 0.056 \pm 0.017 $ and $\delta N_{\rm eff} = 0.41 \pm 0.16$ is preferred by current observations, while the Hubble tension in this model is also alleviated to be $2.2 \sigma$.