Sequence of induced Hausdorff metrics on Lie groups

Abstract

Let $\varphi: G \times (M,d) \rightarrow (M,d)$ be a left action of a Lie group on a differentiable manifold endowed with a metric $d$ (distance function) compatible with the topology of $M$. Denote $gp:=\varphi(g,p)$. Let $X$ be a compact subset of $M$. Then the isotropy subgroup of $X$ is a closed subgroup of $G$ defined as $H_X:=\{g\in G; gX=X\}$. The induced Hausdorff metric is a metric on the left coset manifold $G/H_X$ defined as $d_X(gH_X,hH_X)=d_H(gX,hX)$, where $d_H$ is the Hausdorff distance in $M$. Suppose that $\varphi$ is transitive and that there exist $p\in M$ such that $H_X=H_p$. Then $gH_X \mapsto gp$ is a diffeomorphism that identifies $G/H_X$ and $M$. In this work we define a discrete dynamical system of metrics on $M$. Let $d^1=\hat d_X$, where $\hat d_X$ stands for the intrinsic metric associated to $d_X$. We can iterate $\varphi: G \times (M\equiv G/H_X,d^1)\rightarrow (M\equiv G/H_X,d^1)$, in order to get $d^2, d^3$ and so on. We study the particular case where $M=G$, the left action $\varphi: G\times (G,d) \rightarrow (G,d)$ is the product of $G$, $d$ is bounded above by a right invariant intrinsic metric on $G$ and $X\ni e$ is a finite subset of $G$. We prove that the sequence $d^i$ converges pointwise to a metric $d^\infty$. In addition, if $d$ is complete and the semigroup generated by $X$ is dense in $G$, then $d^\infty$ is the distance function of a right invariant $C^0$-Carnot-Carath\'eodory-Finsler metric. The case where $d^\infty$ is $C^0$-Finsler is studied in detail.