Dispersion and limit theorems for random walks associated with hypergeometric functions of type BC

Abstract

The spherical functions of the noncompact Grassmann manifolds Gp,q(F) = G/K over the (skew-)fields F = R,C,H with rank q ≥ 1 and dimension parameter p > q can be described as Heckman-Opdam hypergeometric functions of type BC, where the double coset space G//K is identified with the Weyl chamber CBq ⊂ ℝq of type B. The corresponding product formulas and Harish-Chandra integral representations were recently written down by M. Rösler and the author in an explicit way such that both formulas can be extended analytically to all real parameters p ∈ [2q − 1, ∞[, and that associated commutative convolution structures *p on CBq exist. In this paper we introduce moment functions and the dispersion of probability measures on depeCBqnding on *p and study these functions with the aid of this generalized integral representation. Moreover, we derive strong laws of large numbers and central limit theorems for associated timehomogeneous random walks on (CBq , *p) where the moment functions and the dispersion appear in order to determine drift vectors and covariance matrices of these limit laws explicitely. For integers p, all results have interpretations for G-invariant random walks on the Grassmannians G/K. Besides the BC-cases we also study the spaces GL(q, F)/U(q, F), which are related to Weyl chambers of type A, and for which corresponding results hold. For the rank-one-case q = 1, the results of this paper are well-known in the context of Jacobi-type hypergroups on [0,∞[.