Fixed sets and free subgroups of groups acting on metric spaces.
Aperiodische Wahrscheinlichkeitsmaße auf topologischen Gruppen.
The Martin Boundary for Harmonic Functions on Groups of Automorphisms of a Homogeneous Tree.
Amenable group actions on infinite graphs.
Erratum: Heat diffusion on homogeneous trees. Note on a paper by G. Medolla and A. G. Setti: Long time heat diffusion on homogeneous trees
Heat diffusion on homogeneous trees (Note on a paper by G. Medolla and A. G. Setti)
Medolla e Setti [6] studiano l'andamento della diffusione del calore generata dal Laplaciano discreto su un albero omogeneo e dimostrano che il calore è asintoticamente concentrato in «anelli» che viaggiano verso l'infinito a velocità lineare e la cui larghezza divisa per tende all'infinito, dove è il tempo. Qui si spiega come un risultato più preciso si ottiene come corollario della legge dei grandi numeri e del teorema del limite centrale per la passeggiata aleatoria sull'albero. Inoltre,...
Random Walks on Amalgams.
The Martin compactification of the Cartesian product of two hyperbolic spaces.
Stochastic dynamical systems with weak contractivity properties I. Strong and local contractivity
Consider a proper metric space and a sequence of i.i.d. random continuous mappings → . It induces the stochastic dynamical system (SDS) starting at x ∈ . In this and the subsequent paper, we study existence and uniqueness of invariant measures, as well as recurrence and ergodicity of this process. In the present first part, we elaborate, improve and complete the unpublished work of Martin Benda on local contractivity, which merits publicity and provides an important tool for studying stochastic...
Stochastic dynamical systems with weak contractivity properties II. Iteration of Lipschitz mappings
In this continuation of the preceding paper (Part I), we consider a sequence of i.i.d. random Lipschitz mappings → , where is a proper metric space. We investigate existence and uniqueness of invariant measures, as well as recurrence and ergodicity of the induced stochastic dynamical system (SDS) starting at x ∈ . The main results concern the case when the associated Lipschitz constants are log-centered. Principal tools are local contractivity, as considered in detail in Part I, the Chacon-Ornstein...
Green kernel estimates and the full Martin boundary for random walks on lamplighter groups and Diestel–Leader graphs
Erratum to : “Green kernel estimates and the full Martin boundary for random walks on lamplighter groups and Diestel–Leader graphs”
Amenability, unimodularity, and the spectral radius of random walks on finite graphs.
Transition operators on co-compact G-spaces.
We develop methods for studying transition operators on metric spaces that are invariant under a co-compact group which acts properly. A basic requirement is a decomposition of such operators with respect to the group orbits. We then introduce reduced transition operators on the compact factor space whose norms and spectral radii are upper bounds for the Lp-norms and spectral radii of the original operator. If the group is amenable then the spectral radii of the original and...
Horocyclic products of trees
Let be homogeneous trees with degrees , respectively. For each tree, let be the Busemann function with respect to a fixed boundary point (end). Its level sets are the horocycles. The horocyclic product of is the graph consisting of all -tuples with , equipped with a natural neighbourhood relation. In the present paper, we explore the geometric, algebraic, analytic and probabilistic properties of these graphs and their isometry groups. If and then we obtain a Cayley graph of the...
Random walks on the affine group of local fields and of homogeneous trees
The affine group of a local field acts on the tree (the Bruhat-Tits building of ) with a fixed point in the space of ends . More generally, we define the affine group of any homogeneous tree as the group of all automorphisms of with a common fixed point in , and establish main asymptotic properties of random products in : (1) law of large numbers and central limit theorem; (2) convergence to and solvability of the Dirichlet problem at infinity; (3) identification of the Poisson boundary...
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