The first second of leptons

Stuke, Maik

We study the influence of lepton asymmetries on the evolution of the early Universe. The lepton asymmetry l is poorly constrained by observations and might be orders of magnitudes larger than the observed baryon asymmetry b~O(10^{-10}), |l|/b~O(10^9).
We find that lepton asymmetries 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. For tiny or vanishing baryon and lepton asymmetries lattice QCD simulations show that the cosmic QCD transition is a rapid crossover. However, for large lepton asymmetry, the order of the cosmic transition remains unknown.
We find that a large asymmetry in one or more lepton flavour changes the number of helicity degrees of freedom of all particles in equilibrium g_{ast} significantly. For the relic abundance of WIMPs, depending on g_{ast} of all particles at the freeze out temperature 40 GeV > T_fo > 0.4 GeV we find a decreasing of few percent depending on l_f . For an asymmetry of l_f = 0.1 in all three flavour we find a decrease of the relic WIMP abundance for a given freeze out temperature of almost 20 percent.

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