  We analyze a few illustrative examples of scenarios in which relativistic
symmetries are deformed by Planck-scale effects in particle-type-dependent
manner. The novel mathematical structures required by such scenarios are the
mixing coproducts, which govern the (deformed) law of conservation of energy
and momentum when particles with different relativistic properties interact. We
also comment on the relevance of these findings for recent proposals concerning
the possibility that neutrinos might have relativistic properties which are
different from those of photons and/or the possibility that composite particles
might have relativistic properties which are different from those of
fundamental ones.

General Relativity and Quantum Cosmology;High Energy Physics - Theory