  Recent observations of the luminosity-red shift relation of distant type Ia
supernovae established the fact that the expansion of the universe is
accelerated. This is interpreted by saying that there exists some kind of agent
(called dark energy), which exerts an overall repulsive effect on ordinary
matter. Dark energy contributes today in the amount of about 73 % to the total
energy content of the universe, and its spatial distribution is compatible with
perfect uniformity. The simplest possible explanation for dark energy is to
assume that it is just a universal constant, the so called cosmological
constant. This would mean that the background arena for all natural phenomena,
once all physical matter-energy has been ideally removed, is the de Sitter
space time. Thus, the Poincar\'e group should be replaced by the de Sitter
group, and one is naturally led to a reformulation of the theory of special
relativity on these grounds. The absence of a privileged class of equivalent
frames (inertial frames) suggests that, in de Sitter relativity it would be
desirable, to characterize significant physical quantities in an intrinsic way,
namely in a manner independent of the choice of any particular coordinate
patch. In this talk we would like to show how this can be accomplished for any
set of independent conserved quantities along the geodesic motion of a free de
Sitter particle. These quantities allow for a natural discussion of classical
pointlike scattering and decay processes.
