First second of leptons
A poorly constrained parameter in the Standard Model of Cosmology is thelepton asymmetry l = \sum_f l_f=\sum_f(n_f+n_{\nu_f})/s. Each flavour asymmetryl_f with f=e, \mu, {\tau} is the sum of the net particle density of the chargedleptons n_f and their corresponding neutrinos, normalized with the entropydensity s. Constraints on l_f \leq O(0.1) from BBN and CMB allow for leptonflavour asymmetries orders of magnitudes larger then the baryon asymmetry b ~10^{-10}. In this article we show how such large lepton (flavour) asymmetriesinfluence the early universe, in particular the freeze out of WIMPs and thecosmic QCD transition.
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