$\alpha$ and $\beta$ relaxation
2016 Intrinsic correlation between β-relaxation and spatial heterogeneity in a metallic glass
1995 Metallic glasses - general picture
see Internal friction plot - 1986 Low temperature properties of glasses-unsolved problems - A K RAYCHAUDHURI
The key problem in the physics of glass is relaxation and the key question is what is relaxing
While $\alpha$-relaxation involves structural changes (unlocking of liquid-like defects as T increases through Tg) involving higher
energy, $\beta$-relaxation involves localized structural changes. But both of them are classical thermally activated crossing of barriers although not of the pure Arrhenius type. "TLS relaxation" also involves localized structural changes, probably of the same type as in
$\beta$ relaxation but the mechanism of relaxation is quantum mechanical in origin
- $\beta$-relaxation (Boson peak) is related to $TLS$-relaxation