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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)