担当者:Masatoshi Shoji
時間 :10:30-12:00
場所 :理学部1号館908号室

Title:
Massive Neutrinos in Cosmology: Analytic Solutions and Fluid Approximation

Abstract:
We study the evolution of linear density fluctuations of
free-streaming massive neutrinos at redshift of z<1000, with an
explicit justification on the use of a fluid approximation. We solve
the collisionless Boltzmann equation in an Einstein de-Sitter (EdS)
universe, truncating the Boltzmann hierarchy at lmax=1 and 2, and
compare the resulting density contrast of neutrinos, with that of the
exact solutions of the Boltzmann equation that we derive. Roughly
speaking, the fluid approximation is accurate if neutrinos were
already non-relativistic when the neutrino density fluctuation of a
given wavenumber entered the horizon. We find that the fluid
approximation is accurate at sub-percent levels for massive neutrinos
with m > 0.05eV at the scale of k<1.0h/Mpc and redshift of z<100. This
result validates the use of the fluid approximation, at least for the
most massive species of neutrinos suggested by the neutrino
oscillation experiments.



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Last-modified: 2013-11-20 (水) 11:11:54 (1399d)