Issue |
A&A
Volume 456, Number 1, September II 2006
|
|
---|---|---|
Page(s) | 45 - 54 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20054496 | |
Published online | 23 August 2006 |
Cosmological neutrino entanglement and quantum pressure
Geneva Observatory, University of Geneva, 1290 Sauverny, Switzerland
Received:
8
November
2005
Accepted:
3
June
2006
Context. The widespread view that cosmological neutrinos, even if massive,
are well described since the decoupling redshift down to the present epoch by an almost perfectly
collisionless fluid of classical point particles is
re-examined.
Aims. In view of the likely sub-eV rest mass of neutrinos, the main effects due to their fermionic nature are studied.
Methods. By numerical means we calculate the accurate entropy, fugacity and pressure of cosmological neutrinos in the Universe expansion. By solving the Schrödinger equation we derive how and how fast semi-degenerate identical free fermions become entangled.
Results. We find that for sub-eV neutrinos the exchange degeneracy has
significantly increased during the relativistic to
non-relativistic transition epoch at . At all
times neutrinos become entangled in less than
s, much
faster than any plausible decoherence time. The total pressure is
increased by quantum effect from 5% at high redshifts to 68% at
low redshifts with respect to a collisionless classical fluid.
Conclusions. The quantum overpressure has no dynamical consequences in the homogeneous regime at high redshifts, but must be significant for neutrino clustering during the non-linear structure formation epoch at low redshifts.
Key words: cosmology: theory / neutrions / cosmology: large-scale structure of Universe / cosmology: dark matter / elementary particles
© ESO, 2006
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