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arXiv · 0904.3046

The Thermal Abundance of Semi-Relativistic Relics

Manuel Drees·Mitsuru Kakizaki·Suchita Kulkarni
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Abstract

Approximate analytical solutions of the Boltzmann equation for particles that are either extremely relativistic or non-relativistic when they decouple from the thermal bath are well established. However, no analytical formula for the relic density of particles that are semi-relativistic at decoupling is yet known. We propose a new ansatz for the thermal average of the annihilation cross sections for such particles, and find a semi-analytical treatment for calculating their relic densities. As examples, we consider Majorana- and Dirac-type neutrinos. We show that such semi-relativistic relics cannot be good cold Dark Matter candidates. However, late decays of meta-stable semi-relativistic relics might have released a large amount of entropy, thereby diluting the density of other, unwanted relics.

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Manuel Drees, Mitsuru Kakizaki, Suchita Kulkarni. 2009-08-11. The Thermal Abundance of Semi-Relativistic Relics. https://doi.org/10.1103/physrevd.80.043505

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