  Superluminal preons (superbradyons) with a critical speed in vacuum much
larger than the speed of light would, if they exist, play a fundamental role as
constituents of the physical vacuum and of the conventional particles
considered in standard theories. Then, standard Lorentz symmetry and quantum
mechanics would not be ultimate fundamental properties of space-time and
matter. If superbradyons are present as free particles in our Universe, they
are expected to couple very weakly to "ordinary" matter, but they can
spontaneously decay by emitting standard particles until they reach a speed
equal or close to that of light. They would then form a cosmological sea where
the relation between inertial and gravitational masses would differ from
conventional Physics. Superbradyons may be at the origin of cosmological and
astrophysical phenomena usually associated to dark matter, dark energy and
inflation. They can also be a source of conventional cosmic rays of all
energies. In such a scenario, superbradyon spontaneous decays and similar
interactions would be candidates to explain data on electron and positron
abundances (PAMELA, ATIC, Fermi LAT, HESS, PPB-BETS) considered as possible
dark matter signatures. Superbradyons emitting this radiation may even have
comparatively small inertial masses, and kinetic energies not far away from
those of the decay events. But in most cases, such "light" superbradyons could
not be found at accelerator experiments. We comment on several basic physics
and phenomenological issues in connection with the superbradyon hypothesis.
