Sphaleron freeze-in baryogenesis with gravitational waves from the QCD transition

TL;DR

This paper investigates how a primordial lepton asymmetry can induce a first-order QCD phase transition, producing gravitational waves that could be detected to explain the baryon asymmetry of the universe.

Contribution

It provides a more precise calculation of the lepton asymmetry needed for sphaleron freeze-in and improves the QCD phase transition modeling with better agreement to lattice results.

Findings

Lepton asymmetry required is an order of magnitude smaller than previous estimates.

Identifies parameter range for a first-order QCD transition.

Predicts gravitational wave signals detectable by future experiments.

Abstract

A large primordial lepton asymmetry is capable of explaining the baryon asymmetry of the Universe (BAU) through suppression of the electroweak sphaleron rates (``sphaleron freeze-in") which can lead to a first-order cosmic QCD transition with an observable gravitational wave (GW) signal. With next-to-leading order dimensional reduction and the exact 1-loop fluctuation determinant, we accurately compute the lepton asymmetry needed to realize this paradigm, finding it to be an order of magnitude smaller than previous estimates. Further, we apply an improved QCD equation of state capable of describing the phase transition line together with the critical endpoint leading to better agreement with lattice and functional QCD results. Based on this, we identify the range of lepton flavor asymmetries inducing a first-order cosmic QCD transition. We then extract the parameters relevant to the prediction of GW signal from a first-order cosmic QCD transition. Our result showcases the possibility of probing the sphaleron freeze-in paradigm as an explanation of BAU by future gravitational wave experiments like $\mu$Ares.