Tsallis Relative Entropy and Anomalous Diffusion

In this paper we utilize the Tsallis relative entropy, a generalization of the Kullback-Leibler entropy in the frame work of non-extensive thermodynamics to analyze the properties of anomalous diffusion processes. Anomalous (super-) diffusive behavior can be described by fractional diffusion equations, where the second order space derivative is extended to fractional order alpha is an element of (1, 2). They represent a bridging regime, where for alpha = 2 one obtains the diffusion equation and for alpha = 1 the (half) wave equation is given. These fractional diffusion equations are solved by so-called stable distributions, which exhibit heavy tails and skewness. In contrast to the Shannon or Tsallis entropy of these distributions, the Kullback and Tsallis relative entropy, relative to the pure diffusion case, induce a natural ordering of the stable distributions consistent with the ordering implied by the pure diffusion and wave limits.