Abstract
The relic cosmic background neutrinos accompanying the cosmic microwave background(CMB) photons may hide a universal lepton asymmetry orders of magnitudelarger than the universal baryon asymmetry. At present, the only direct way toprobe such an asymmetry is through its effect on the abundances of the lightelements produced during primordial nucleosynthesis. The relic light elementabundances also depend on the baryon asymmetry, parameterized by the baryondensity parameter () and on the early-universe expansion rate, parameterized by the expansion rate factor () or, equivalently, by the effective number of neutrinos (). We use data from the CMB (and large scale structure: LSS) along withthe observationally inferred relic abundances of deuterium and helium-4to provide new bounds on the universal lepton asymmetry, finding forηL, the analogof ηB,0.072 ± 0.053 if it isassumed that Nν = 3 and, 0.115 ± 0.095 along with Nν = 3.3−0.6+0.7, if Nν is free to vary.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
