Aging in models of nonlinear diffusion

We show that for a class of problems described by the nonlinear diffusion equation ∂/∂t${\mathrm{\phi }}^{\mathrm{\mu }}$=D${\mathrm{\partial }}^2$/∂${\mathrm{x}}^2$ ${\mathrm{\phi }}^{\nu }$ an exact calculation of the two time autocorrelation function gives C(t,${\mathrm{t}}^{|\mathrm{I}\mathrm{H}}$)=f(t-${\mathrm{t}}^{|\mathrm{I}\mathrm{H}}$)g(${\mathrm{t}}^{|\mathrm{I}\mathrm{H}}$) (t>${\mathrm{t}}^{|\mathrm{I}\mathrm{H}}$) exhibiting normal and anomalous diffusions, as well as aging effects, depending on the values of μ and ν. We also discuss the form in which the fluctuation-dissipation theorem is violated in this type of systems. Finally, we argue that in this kind of model, aging may be a consequence of the nonconservation of the ``total mass.''