Garrido Pedro, Gallavotti Giovanni
Billiards correlation functions
(714K, TeX)

ABSTRACT.  We discuss various experiments on the time decay of velocity
autocorrelation functions in billiards.  We perform new experiments and
find results which are compatible with an exponential mixing hypothesis,
first put forward by [FM]: they do not seem compatible with the
stretched exponentials believed, in spite of [FM], to describe the
mixing. The analysis led us to several byproducts: we obtain information
about the normal diffusive nature of the motion and we consider the
probability distribution of the number of collisions in time $t_m$ (as
$t_m\to\io$) finding a strong dependence on some geometric
characteristics of the locus of the billiards obstacles.