First second of leptons

TL;DR

This paper investigates how large lepton flavor asymmetries, which are weakly constrained, could significantly impact early universe processes like WIMP freeze-out and the QCD transition.

Contribution

It demonstrates the potential effects of large lepton asymmetries on key cosmological events, expanding understanding beyond standard assumptions.

Findings

Large lepton asymmetries can alter WIMP freeze-out conditions.

Lepton asymmetries influence the timing and nature of the QCD transition.

Constraints from BBN and CMB still allow for significant lepton asymmetries.

Abstract

A poorly constrained parameter in the Standard Model of Cosmology is the lepton asymmetry l = \sum_f l_f=\sum_f(n_f+n_{\nu_f})/s. Each flavour asymmetry l_f with f=e, \mu, {\tau} is the sum of the net particle density of the charged leptons n_f and their corresponding neutrinos, normalized with the entropy density s. Constraints on l_f \leq 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.