English

Inverted orbits of exclusion processes, diffuse-extensive-amenability and (non-?)amenability of the interval exchanges

Group Theory 2020-01-07 v4 Functional Analysis Probability

Abstract

The recent breakthrough works [6,8,9] which established the amenability for new classes of groups, lead to the following question: is the action W(Zd)ZdW(\mathbb{Z}^d) \curvearrowright \mathbb{Z}^d extensively amenable? (Where W(Zd)W(\mathbb{Z}^d) is the {\em wobbling group} of permutations σ:ZdZd\sigma:\mathbb{Z}^d \to \mathbb{Z}^d with bounded range). This is equivalent to asking whether the action (Z/2 Z)(Zd)W(Zd)(Z/2Z)(Zd)(\mathbb{Z}/2\ \mathbb{Z})^{(\mathbb{Z}^d)} \rtimes W(\mathbb{Z}^d) \curvearrowright (\mathbb{Z}/2\mathbb{Z})^{(\mathbb{Z}^d)} is amenable. The d=1d=1 and d=2d=2 and have been settled respectively in [6,8]. By [9], a positive answer to this question would imply the amenability of the IET group. In this work, we give a partial answer to this question by introducing a natural strengthening of the notion of extensive-amenability which we call diffuse-extensive-amenability. Our main result is that for any bounded degree graph XX, the action W(X)XW(X)\curvearrowright X is diffuse-extensively amenable if and only if XX is recurrent. Our proof is based on the construction of suitable stochastic processes (τt)t0(\tau_t)_{t\geq 0} on W(X)<S(X)W(X)\, <\, \mathfrak{S}(X) whose {\em inverted orbits} Oˉt(x0)={xX,st,τs(x)=x0}=0stτs1({x0}) \bar O_t(x_0) = \{x\in X, \exists s\leq t,\, \tau_s(x)=x_0\} = \bigcup_{0\leq s \leq t} \tau_s^{-1}(\{x_0\}) are exponentially unlikely to be sub-linear when XX is transient. This result leads us to conjecture that the action W(Zd)ZdW(\mathbb{Z}^d) \curvearrowright \mathbb{Z}^d is not extensively amenable when d3d\geq 3 and that a different route towards the (non-?)amenability of the IET group may be needed.

Keywords

Cite

@article{arxiv.1804.01981,
  title  = {Inverted orbits of exclusion processes, diffuse-extensive-amenability and (non-?)amenability of the interval exchanges},
  author = {Christophe Garban},
  journal= {arXiv preprint arXiv:1804.01981},
  year   = {2020}
}

Comments

23 pages (minor changes)