The Hubble Tension as a Hint of Leptogenesis and Neutrino Mass Generation

TL;DR

This paper explores how a majoron, linked to neutrino mass models, can help resolve the Hubble tension by naturally producing dark radiation through low-scale leptogenesis, connecting neutrino physics with cosmological observations.

Contribution

It demonstrates that models of low-scale leptogenesis can generate primordial majorons that contribute to dark radiation, alleviating the Hubble tension without additional assumptions.

Findings

Majorons can damp neutrino free-streaming and increase energy density.

Leptogenesis models can produce primordial majorons from sterile neutrino decays.

Expected H0 value aligns with SH0ES measurements at about 10% probability.

Abstract

The majoron, a neutrinophilic pseudo-Goldstone boson conventionally arising in the context of neutrino mass models, can damp neutrino free-streaming and inject additional energy density into neutrinos prior to recombination. The combination of these effects for an eV-scale mass majoron has been shown to ameliorate the outstanding $H_0$ tension, however only if one introduces additional dark radiation at the level of $\Delta N_{\rm eff} \sim 0.5$. We show here that models of low-scale leptogenesis can naturally source this dark radiation by generating a primordial population of majorons from the decays of GeV-scale sterile neutrinos in the early Universe. Using a posterior predictive distribution conditioned on Planck2018+BAO data, we show that the value of $H_0$ observed by the SH$_0$ES collaboration is expected to occur at the level of $\sim 10\%$ in the primordial majoron cosmology (to be compared with $\sim 0.1\%$ in the case of $\Lambda$CDM). This insight provides an intriguing connection between the neutrino mass mechanism, the baryon asymmetry of the Universe, and the discrepant measurements of $H_0$.