Groupe de Physique Statistique

Local scale invariance for ageing systems without detailed balance is tested through studying the dynamical symmetries of the critical bosonic contact process and the critical bosonic pair-contact process. Their field-theoretical actions can be split into a Schroedinger-invariant term and a pure noise term. It is shown that the two-time response and correlation functions are reducible to certain multipoint response functions which depend only on the Schroedinger-invariant part of the action. For the bosonic contact process, the representation of the Schroedinger group can be derived from the free diffusion equation, whereas for the bosonic pair-contact process, a new representation of the Schroedinger group related to a nonlinear Schroedinger equation with dimensionful couplings is constructed. The resulting predictions of local scale invariance for the two-time responses and correlators are completely consistent with the exactly-known results in both models.