Comment on ``Neutrino oscillations in the early universe: how can large lepton asymmetry be generated?"

Abstract

We comment on the recent paper by A. D. Dolgov, S. H. Hansen, S. Pastor and D. V. Semikoz (DHPS) [Astropart. Phys. {\bf 14}, 79 (2000)] on the generation of neutrino asymmetries from active-sterile neutrino oscillations. We demonstrate that the approximate asymmetry evolution equation obtained therein is an expansion, up to a minor discrepancy, of the well-established static approximation equation, valid only when the supposedly new higher order correction term is small. In the regime where this so-called ``back-reaction'' term is large and artificially terminates the asymmetry growth, their evolution equation ceases to be a faithful approximation to the Quantum Kinetic Equations (QKEs) simply because pure Mikheyev-Smirnov-Wolfenstein (MSW) transitions have been neglected. At low temperatures the MSW effect is the dominant asymmetry amplifier. Neither the static nor the DHPS approach contains this important physics. Therefore we conclude that the DHPS results have sufficient veracity at the onset of explosive asymmetry generation, but are invalid in the ensuing low temperature epoch where MSW conversions are able to enhance the asymmetry to values of order $0.2-0.37$. DHPS do claim to find a significant final asymmetry for very large $\delta m^2$ values. However, for this regime the effective potential they employed is not valid.

RevTeX, 32 pages, including 4 embedded figures; this version to appear in Astropart.Phys

References in corpus (8)

• Neutrino oscillations in the early universe: How large lepton asymmetry can be generated?
• Further studies on relic neutrino asymmetry generation I: the adiabatic Boltzmann limit, non-adiabatic evolution, and the classical harmonic oscillator analogue of the quantum kinetic equations
• Further studies on relic neutrino asymmetry generation II: a rigorous treatment of repopulation in the adiabatic limit
• The ${\nu }_{\mu }\leftrightarrow {\nu }_s$ interpretation of the atmospheric neutrino data and cosmological constraints
• On chaoticity of the amplification of the neutrino asymmetry in the early universe
• On the sign of the neutrino asymmetry induced by active-sterile neutrino oscillations in the early Universe
• Amplification of Isocurvature Perturbations induced by Active-Sterile Neutrino Oscillations
• Physical origin of "chaoticity" of neutrino asymmetry

Cited by in corpus (11)

• Probing oscillations into sterile neutrinos with cosmology, astrophysics and experiments
• Do many-particle neutrino interactions cause a novel coherent effect?
• Sterile neutrinos, lepton asymmetries, primordial elements: how much of each?
• Light sterile neutrino production in the early universe with dynamical neutrino asymmetries
• Update on neutrino mixing in the early Universe
• Neutrino Propagation in Dense Astrophysical Systems
• Can active-sterile neutrino oscillations lead to chaotic behavior of the cosmological lepton asymmetry?
• Oscillation Induced Neutrino Asymmetry Growth in the Early Universe
• Active-sterile neutrino oscillations in the early Universe: asymmetry generation at low |delta m^2| and the Landau-Zener approximation
• Entanglement and quantal coherence: a study of two limiting cases of rapid system--bath interactions
• Neutrino oscillations and Big Bang Nucleosynthesis