Cells and cacti

Abstract

Let $(W,S)$ be a Coxeter system, let $\varphi$ be a weight function on $S$ and let ${\mathrm{Cact}}\_W$ denote the associated {\it cactus group}. Following an idea of I. Losev, we construct an action of ${\mathrm{Cact}}\_W \times {\mathrm{Cact}}\_W$ on $W$ which has nice properties with respect to the partition of $W$ into left, right or two-sided cells (under some hypothesis, which hold for instance if $\varphi$ is constant or if $W$ is finite of rank \textless{} 5). It must be noticed that the action depends heavily on $\varphi$.Comment: 23 pages. This new version extends the scope of validity of the main result by removing an hypothesis. For this purpose, we have slightly extended some results of arXiv:1502.0166