Speaker
Description
The lattice QCD simulations predict a slow cross-over from parton to hadron matter, especially at small baryon densities. When attempting to apply this to the early universe, we find that the latest non-leptonic phase transition would not account for the large-scale structure of the universe. In the early epochs of the evolution of the universe, it is conjectured that the baryonic density, especially after the era of quark-gluon plasma, is negligibly small. On the other hand, the leptonic degrees of freedom likely survive the strong parton–hadron phase transition. Accordingly, the lepton chemical potential apparently remains finite, while the baryon chemical potential is nearly vanishing. In a thermal model with the entire PDG compilation, we analysed how the temperature varies with the lepton density. The dependence of the critical temperature on the lepton density maps out a richly structured phase diagram that might contribute to understanding the large-scale structure of the universe.
