  We study the effect of initial correlations on the short-time decoherence of
a particle linearly coupled to a bath of harmonic oscillators. We analytically
evaluate the attenuation coefficient of a Schroedinger cat state both for a
free and a harmonically bound particle, with and without initial thermal
correlations between the particle and the bath. While short-time decoherence
appears to be independent of the system in the absence of initial correlations,
we find on the contrary that, for initial thermal correlations, decoherence
becomes system dependent even for times much shorter than the characteristic
time of the system. The temperature behavior of this system dependence is
discussed.
