Thermodynamics of the Glassy State: Effective Temperature as an Additional System Parameter

A system is glassy when the observation time is much smaller than the equilibration time. A unifying thermodynamic picture of the glassy state is presented. Slow configurational modes are in quasiequilibrium at an effective temperature. It enters thermodynamic relations with the configurational entropy as a conjugate variable. Slow fluctuations contribute to susceptibilities via quasiequilibrium relations, while there is also a configurational term. Fluctuation-dissipation relations also involve the effective temperature. Fluctuations in the energy are nonuniversal, however. The picture is supported by analytically solving the dynamics of a toy model.