Cosmic QCD Epoch at Nonvanishing Lepton Asymmetry.

Area of Science:

• Early Universe cosmology
• Quantum Chromodynamics (QCD) phase diagram
• Particle physics

Background:

• The early Universe's evolution is governed by the behavior of matter under extreme conditions.
• Understanding the Quantum Chromodynamics (QCD) phase diagram is crucial for modeling the early Universe.
• Lepton and baryon asymmetries are fundamental properties of the Universe.

Purpose of the Study:

• To investigate the impact of lepton asymmetry on the cosmic trajectory in the QCD phase diagram.
• To analyze the evolution of chemical potentials during the QCD epoch.
• To compare trajectories with standard assumptions versus larger lepton asymmetries.

Main Methods:

• Utilizing lattice QCD calculations to determine susceptibilities.
• Interpolating between ideal quark gas and ideal hadron resonance gas models.
• Studying the evolution of chemical potentials (lepton, baryon, charge).

Main Results:

• Lepton asymmetry affects the evolution of all chemical potentials.
• A larger lepton asymmetry causes the charge chemical potential to exceed the baryon chemical potential.
• This crossover occurs before the pion annihilation phase.

Conclusions:

• Lepton asymmetry plays a critical role in shaping the early Universe's thermodynamic trajectory.
• The standard cosmic trajectory assumes negligible lepton asymmetry, which may not hold true.
• Deviations from the standard trajectory due to lepton asymmetry have significant implications for early Universe models.