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OATS-DAUT SEMINAR
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Speaker: Theo M. Nieuwenhuizen (Institute for Theoretical Physics, Amsterdam, NL)
Title: On the neutrino mass and neutrinos as the hot dark matter
Date: Wednesday, September 9th, 2009
Time: 16:00
Venue: Villa Bazzoni
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Abstract: The dark matter of the Abell 1689 galaxy cluster is
modeled by a thermal distribution of non-relativistic gravitating fermions
and the galaxies and gas by isothermal distributions. A fit yields a fermion
mass of about 1.5 eV, depending on the Hubble constant and the number of
fermionic degrees of freedom. A dark matter fraction of 0.19 is achieved
for 3 families of left plus right handed neutrinos with nearly equal masses.
Given a temperature of 0.046 K and a de Broglie length of 0.20 mm, they
establish a quantum structure of several million light years across, this
being the largest known particle-based quantum structure in the Universe.
The predicted alpha-particle temperature of 10 keV coincides with the one
of X-rays. The righthanded neutrino states can be filled in the early
Universe provided that there are meV Majorana mass terms, which can be
tested in neutrinoless double beta-decay. Nucleosynthesis is modified by
the extra neutrinos, but it can be repaired by assuming slightly more
neutrinos than antineutrinos. This dark matter is hot, i. e., nearly
relativistic at decoupling. In the expanding Universe, the neutrino free
streaming stops when they condense on the galaxy cluster; this causes
reionization of the cluster gas without help of heavy stars.
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contact: Andrea Biviano (OATS)