Journal Article

Model-independent analysis of dark matter points to a particle mass at the keV scale

H. J. de Vega and N. G. Sanchez

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 404, issue 2, pages 885-894
Published in print May 2010 | ISSN: 0035-8711
Published online May 2010 | e-ISSN: 1365-2966 | DOI:
Model-independent analysis of dark matter points to a particle mass at the keV scale

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We present a model-independent analysis of dark matter (DM) decoupling both ultrarelativistically (UR) and non-relativistically (NR) based on the DM phase-space density . We derive explicit formulae for the DM particle mass m and for the number of ultrarelativistic degrees of freedom gd at decoupling. We find that for DM particles decoupling UR both at local thermal equilibrium (LTE) and out of LTE, m turns out to be in the keV scale. For example, for DM Majorana fermions decoupling at LTE the resulting mass is m≃ 0.85 keV. For DM particles decoupling NR, results in the keV scale (Td is the decoupling temperature) and the value of m is consistent with the keV scale. In all cases, DM turns out to be cold DM (CDM). In addition, lower and upper bounds on the DM annihilation cross-section for NR decoupling are derived. We evaluate the free-streaming (Jeans) wavelength and Jeans mass: they are independent of the type of DM except for the DM self-gravity dynamics. The free-streaming wavelength today turns to be in the kpc range. These results are based on our theoretical analysis, on astronomical observations of dwarf spheroidal satellite galaxies in the Milky Way and on N-body numerical simulations. We analyse and discuss the results for from analytic approximate formulae for both linear fluctuations and the (non-linear) spherical model and from N-body simulations results. In this way we obtain upper bounds for the DM particle mass, which are all below the 100-keV range.

Keywords: galaxies: fundamental parameters; cosmology: theory; dark matter

Journal Article.  6427 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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