Abstract
We propose a scenario for the glass transition based on the cooperative nature of nucleation processes and entropic effeets. The main point is the relation between the off-equilibrium energy dissipation and nucleation processes in off-equilibrium supercooled liquids which leads to a natural definition of the complexity. From the absence of coarsening growth we can derive an entropy-based fluctuation formula which relates the free-energy dissipation rate in the glass to the nucleation rate of the largest cooperative regions. As a by-product we obtain a new phenomenological relation between the longest relaxation time in the supercooled liquid phase and an effective temperature. This differs from the Adam-Gibbs relation in that it predicts no divergence of the primary relaxation time at the Kauzmann temperature and the existence of a crossover from fragile to strong behaviour.