2000/05/23 by M. Orito, T. Kajino, Orito, M. +6
Physics and Astronomy · #Astrophysics (astro-ph) #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #Nuclear Theory (nucl-th) #Particle physics theoretical and experimental studies #astro-ph #hep-ph #nucl-th
paper · pdf · doi:10.48550/arxiv.astro-ph/0005446
Revised version submitted to ApJ
openalex publication_date 2000/05/23 · arxiv created 2001/02/22 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We reanalyze the cosmological constraints on the existence of a net universal lepton asymmetry and neutrino degeneracy. We show that neutrinos can begin to decouple at higher temperatures than previous estimates due to several corrections which diminish the neutrino reaction rate. These decoupled neutrinos are therefore not heated as the particle degrees of freedom change. The resultant ratio of the relic neutrino-to-photon temperatures after e^± annihilation can then be significantly reduced by more than a factor of two from that of the standard nondegenerate ratio. This changes the expansion rate and subsequent primordial nucleosynthesis, photon decoupling, and structure formation. In particular we analyze physically plausible lepton-asymmetric models with large νμ and ντ degeneracies together with a moderate νe degeneracy. We show that the nucleosynthesis by itself permits very large neutrino degeneracies 0 ≤ \xinum, \xinut ≤ 40, 0 ≤ \xinue ≤ 1.4 together with large baryon densities 0.1 ≤ Ωb \h502 ≤ 1 as long as some destruction of primordial lithium has occurred. We also show that structure formation and the power spectrum of the cosmic microwave background allows for the possibility of an Ω= 1, ΩΛ= 0.4, cosmological model for which there is both significant lepton asymmetry (| \xinum | = | \xinut | ≈ 11) and a relatively large baryon density (Ωb \h502 ≈ 0.2). Our best-fit neutrino-degenerate, high-baryon-content models are mainly distinguished by a suppression of the second peak in the microwave background power spectrum. This is consistent with the recent high resolution data from BOOMERANG and MAXIMA-1.