  We show that hydrodynamic collision processes of graphene at the neutrality
point can be described in terms of a Fokker-Planck equation with fractional
derivative, corresponding to a L\'evy flight in momentum space. Thus,
electron-electron collisions give rise to frequent small-angle scattering
processes that are interrupted by rare large-angle events. The latter give rise
to superdiffusive dynamics of collective excitations. We argue that such
superdiffusive dynamics is of more general importance to the out-of-equilibrium
dynamics of quantum-critical systems.
