Tsallis entropy induced metrics and CAT(k) spaces
  Generalizing the group structure of the Euclidean space, we construct a Riemannian metric on the deformed set \ $\mathbb{R}^n_q$ \ induced by the Tsallis entropy composition property. We show that the Tsallis entropy is a "hyperbolic analogue" of the "Euclidean" Boltzmann/Gibbs/Shannon entropy and find a geometric interpretation for the nonextensive parameter $q$. We provide a geometric explanation of the uniqueness of the Tsallis entropy as reflected through its composition property, which is provided by the Abe and the Santos axioms. For two, or more, interacting systems described by the Tsallis entropy, having different values of $q$, we argue why a suitable extension of this construction is provided by the Cartan/Alexandrov/Toponogov metric spaces with a uniform negative curvature upper bound. 
Nikos Kalogeropoulos
math-ph cond-mat.stat-mech gr-qc math.MP