Dr. Oleg Ruchayskiy

Free streaming of particles

by Oleg Ruchayskiy

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To quantify the clustering properties of DM one defines a comoving free streaming horizon via
where is a scale factor, is the time today (see the age of the Universe) and is the velocity of DM particles. The velocity is given by the following expression
where is the speed of light and time of non-relativistic transition is defined as the time when
where is the mass of the DM particle.
Alternative definitions:
Ontology information:
Free streaming of particles
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