Lepton asymmetry and the cosmic QCD transition

TL;DR

This paper investigates how large lepton asymmetries in the early universe can significantly alter the QCD phase transition, potentially making it first order, which impacts cosmological evolution.

Contribution

It demonstrates that significant lepton asymmetries can change the nature of the QCD transition and affect the cosmic trajectory in the phase diagram.

Findings

Large lepton asymmetries influence the QCD phase transition dynamics.

Lepton asymmetry can turn the transition into a first-order phase change.

The cosmic trajectory in the phase diagram depends on lepton asymmetry.

Abstract

We study the influence of lepton asymmetry on the evolution of the early Universe. The lepton asymmetry $l$ is poorly constrained by observations and might be orders of magnitude larger than the baryon asymmetry $b$, $|l|/b \leq 2\times 10^8$. We find that lepton asymmetries that are large compared to the tiny baryon asymmetry, can influence the dynamics of the QCD phase transition significantly. The cosmic trajectory in the $\mu_B-T$ phase diagram of strongly interacting matter becomes a function of lepton (flavour) asymmetry. Large lepton asymmetry could lead to a cosmic QCD phase transition of first order.