•Unknown particles
decouple early but not before
they become non-relativistic.
•The cold dark
matter perturbations grow from these
early times and are unaffected by some damping processes that HDM experiences.
•Perturbations
survive on all scales leading to structure
on all scales, as observed.
•Small structures
form first, “hierarchical” galaxy
formation.
•Can be studied in
detail via computer simulations.
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