  Effects of velocity dispersion of dark matter particles on the CMB TT power
spectrum and on the matter linear power spectrum are investigated using a
modified CAMB code. Cold dark matter originated from thermal equilibrium
processes does not produce appreciable effects but this is not the case if
particles have a non-thermal origin. A cut-off in the matter power spectrum at
small scales, similar to that produced by warm dark matter or that produced in
the late forming dark matter scenario, appears as a consequence of velocity
dispersion effects, which act as a pressure perturbation.
