Sobolev index: A classification of L\'evy processes

TL;DR

This paper introduces a classification of Lévy processes based on the Sobolev index derived from their symbols, linking process structure to solution spaces of associated PDEs and applications like option pricing.

Contribution

It defines the Sobolev index for Lévy processes and demonstrates its applicability to various processes, connecting it with path variation and distribution smoothness.

Findings

The Sobolev index determines the unique weak solution space for associated PDEs.

The classification applies to processes like Brownian motion, GH, CGMY, and stable Lévy processes.

Comparison with the Blumenthal-Getoor index reveals insights into process smoothness and path variation.

Abstract

We classify L\'evy processes according to the solution spaces of the associated parabolic PIDEs. This classification reveals structural characteristics of the processes and is relevant for applications such as for solving PIDEs numerically for pricing options in L\'evy models. The classification is done via the Fourier transform i.e. via the symbol of the process. We define the Sobolev index of a L\'evy process by a certain growth condition on the symbol. It follows that for L\'evy processes with Sobolev index $\alpha$ the corresponding evolution problem has a unique weak solution in the Sobolev-Slobodeckii space $H^{\alpha/2}$. We show that this classification applies to a wide range of processes. Examples are the Brownian motion with or without drift, generalised hyperbolic (GH), CGMY and (semi) stable L\'evy processes. A comparison of the Sobolev index with the Blumenthal-Getoor index sheds light on the structural implication of the classification. More precisely, we discuss the Sobolev index as an indicator of the smoothness of the distribution and of the variation of the paths of the process. This highlights the relation between the $p$-variation of the paths and the degree of smoothing effect that stems from the distribution.