Fugacity and reheating of primordial neutrinos

Jeremiah Birrell, Cheng Tao Yang, Pisin Chen, Johann Rafelski

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


We clarify in a quantitative way the impact that distinct chemical T c and kinetic Tk freeze-out temperatures have on the reduction of the neutrino fugacity Υν below equilibrium, i.e. Υν<1, and the increase of the neutrino temperature T ν via partial reheating. We establish the connection between Υν and Tk via the modified reheating relation Tνν)/Tγ, where T γ is the temperature of the background radiation. Our results demonstrate that one must introduce the chemical nonequilibrium parameter, i.e. the fugacity, Υν, as an additional standard cosmological model parameter in the evaluation of CMB fluctuations as its value allows measurement of Tk.

Original languageEnglish (US)
Article number1350188
JournalModern Physics Letters A
Issue number40
StatePublished - Dec 28 2013


  • Big bang nucleosynthesis
  • Elementary particle processes
  • Kinetic and transport theory of gases
  • Neutrino mass and mixing

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Astronomy and Astrophysics
  • Physics and Astronomy(all)


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