The dynamical scaling of ageing ferromagnetic systems can be generalized to a local scale invariance. This yields a prediction for the causal two-time response function, which has been numerically confirmed in the Glauber-Ising model quenched into the ordered phase. For a dynamical exponent z=2, a new embedding of the Schr\"odinger group into the conformal group and the resulting conditions for the validity of local scale invariance are discussed.
Categories: cond-mat.stat-mech hep-th math-ph math.MP