Persistently Non-Gaussian Metastable Liquids

Particles undergoing Fickian diffusion within smooth energy landscapes exhibit Gaussian statistics. However, this Gaussian behavior is often elusive in complex liquids, where particle dynamics within spontaneously fluctuating or spatio-temporally heterogeneous environments lead to a breakdown of ergodicity and time-reversal symmetry. This is usually caused by extreme particle movements or sudden dynamical arrest. Such situations are prevalent in dense metastable liquids exhibiting slow flow or cooperative movements, facilitated by cage-breaking. We investigate the dynamics of glassy systems driven by either thermal, external, or environmental fluctuations. Despite their differences, our findings reveal that particle motion is universally affected by large deviations, resulting in non-Gaussian tails persisting over multiple decades in time. We further discuss the underlying dynamical aspects.