First second of leptons
Abstract
A poorly constrained parameter in the Standard Model of Cosmology is the lepton asymmetry l = Σf lf=Σf(nf+n_f)/s. Each flavour asymmetry lf with f=e, μ, τ is the sum of the net particle density of the charged leptons nf and their corresponding neutrinos, normalized with the entropy density s. Constraints on lf ≤ O(0.1) from BBN and CMB allow for lepton flavour asymmetries orders of magnitudes larger then the baryon asymmetry b ~ 10-10. In this article we show how such large lepton (flavour) asymmetries influence the early universe, in particular the freeze out of WIMPs and the cosmic QCD transition.
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