Small Deviations of Stable Processes and Entropy of the Associated Random Operators

We investigate the relation between the small deviation problem for a symmetric α-stable random vector in a Banach space and the metric entropy properties of the operator generating it. This generalizes former results due to Li and Linde and to Aurzada. It is shown that this problem is related to the study of the entropy numbers of a certain random operator. In some cases an interesting gap appears between the entropy of the original operator and that of the random operator generated by it. This phenomenon is studied thoroughly for diagonal operators. Basic ingredient here are techniques related to random partitions of the integers. The main result about metric entropy and small deviation allows us to determine or provide new estimates for the small deviations rate for several symmetric α-stable random processes, among them unbounded Riemann-Liouville processes, weighted Riemann-Liouville processes, and the (d-dimensional) α-stable sheet.