Sub-aging in a Domain Growth Model

We study analytically the aging dynamics of the O(n) model in the large-n limit, with conserved and with non-conserved order parameter. While in the non-conserved dynamics, the autocorrelation function scales in the usual way C(t,tw) = C(t/tw), in the case of a conserved order parameter, `multiscaling' manifests itself in the form C(t,tw) = C (h(t)/h(tw)), with a relaxation time growing more slowly than the age of the system (sub-aging), and h(t) a function growing faster than any length scale of the problem. In both cases, the effective temperature associated to the violation of the fluctuation theorem tends to infinity in the asymptotic limit of large waiting times.