Fast and slow relaxation processes in glasses

We present dielectric relaxation (DS) and light scattering (LS) data of sev eral glass formers. Relaxational features are compiled which are not yet pr operly taken into account by current models. (i) We distinguish two types o f glass formers. Type A systems do not show a slow beta-process whereas typ e B systems do. A full line-shape analysis of epsilon(omega) is presented ( 10(-2) Hz < v < 10(9) Hz). In type A systems the evolution of the high-freq uency wing of the cu-process is the most prominent spectral change while co oling and leads to an essentially constant loss at T < T-g The analysis of epsilon(omega) of type B systems is carried out within the Williams-Watts a pproach and we focus on the temperature dependence of the B-relaxation stre ngth. (ii) Concerning fast relaxations below Tg as revealed by LS (10(9) Hz < v < 10(13) Hz) we identify relaxation with a low-frequency power-law beh aviour. No indication of a crossover to a white noise spectrum as previousl y reported and discussed within MCT is found. Analysing this relaxation we recourse to the model of thermally activated transitions in asymmetric doub le well potentials. We show that the model works well in some cases and the distribution of barrier heights may be extracted, but in other systems pro nounced deviations occur.