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Open Access Publications from the University of California

Effect of neutrino rest mass on ionization equilibrium freeze-out

  • Author(s): Grohs, E
  • Fuller, GM
  • Kishimoto, CT
  • Paris, MW
  • et al.

© 2015 American Physical Society. We show how small neutrino rest masses can increase the expansion rate near the photon decoupling epoch in the early Universe, causing an earlier, higher temperature freeze-out for ionization equilibrium compared to the massless neutrino case. This yields a larger free-electron fraction, thereby affecting the photon diffusion length differently than the sound horizon at photon decoupling. This neutrino-mass and recombination effect depends strongly on the neutrino rest masses. Though below current sensitivity, this effect could be probed by next-generation cosmic microwave background experiments, giving another observational handle on neutrino rest mass.

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