PUB - Publikationen an der Universität Bielefeld

The lepton asymmetry of the universe is just weakly constraint and might be orders of magnitude larger than the baryon asymmetry. In this thesis, we investigate how a lepton asymmetry influences the cosmic trajectory through the phase diagram of Quantum Chromodynamics (QCD). Therefore, we develop a technique to determine the temperature evolution of chemical potentials during the QCD epoch of the early universe at arbitrary lepton flavor asymmetries. We will rely on an ideal quark gas approximation at high temperatures, T > 150 MeV, and a hadron resonance gas model at low temperatures, T < 250 MeV. Higher-order perturbative corrections are (partially) included in the ideal quark gas approximation. To interpolate between these approximations, we will for the first time use lattice QCD susceptibilities to properly account for strong interaction effects close to the QCD transition temperature TQCD. We therefore use a Taylor series ansatz of the QCD pressure up to second order in the chemical potentials. With this technique we investigate the impact of equally and unequally distributed lepton flavor asymmetries on the cosmic trajectory. We conclude with an estimate on the reliability of our technique via using a Taylor series of the QCD pressure.