  We consider a simple model of a structural glass, represented by a lattice
gas with kinetic constraints in contact with a particle reservoir. Quench below
the glass transition is represented by the jump of the chemical potential above
a threshold. After a quench, the density approaches the critical density-where
the diffusion coefficient of the particles vanishes-following a power law in
time. In this regime, the two-time self-correlation functions exhibit aging.
The behavior of the model can be understood in terms of simple mean-field
arguments.
