English

Dynamics of Pop-Tsack Torsing

Combinatorics 2022-09-26 v1

Abstract

For a finite irreducible Coxeter group (W,S)(W,S) with a fixed Coxeter element cc and set of reflections TT, Defant and Williams define a pop-tsack torsing operation Popt ⁣:WW\mathrm{Popt}\colon W \to W given by Popt(w)=wπT(w)1\mathrm{Popt}(w) = w \cdot \pi_T(w)^{-1} where πT(w)=tTw, tTNC(w,c)t\pi_T(w) = \bigvee_{t \leq_{T}w, \ t \in T}^{NC(w,c)}t is the join of all reflections lying below ww in the absolute order in the non-crossing partition lattice NC(w,c)NC(w,c). This is a "dual" notion of the pop-stack sorting operator Pops\mathrm{Pops} introduced by Defant as a way to generalize the pop-stack sorting operator on Sn\mathfrak{S}_n to general Coxeter groups. Define the forward orbit of an element wWw \in W to be OPopt(w)={w,Popt(w),Popt2(w),}O_{\mathrm{Popt}}(w) = \{w, \mathrm{Popt}(w), \mathrm{Popt}^2(w), \ldots \}. Defant and Williams established the length of the longest possible forward orbits maxwWOPopt(w)\max_{w \in W}|O_{\mathrm{Popt}}(w)| for Coxeter groups of coincidental types and type DD in terms of the corresponding Coxeter number of the group. In their paper, they also proposed multiple conjectures about enumerating elements with near maximal orbit length. We resolve all the conjectures that they have put forth about enumeration, and in the process we give complete classifications of these elements of Coxeter groups of types A,BA,B and DD with near maximal orbit lengths.

Keywords

Cite

@article{arxiv.2209.11548,
  title  = {Dynamics of Pop-Tsack Torsing},
  author = {Anqi Li},
  journal= {arXiv preprint arXiv:2209.11548},
  year   = {2022}
}

Comments

26 pages, 19 figures. arXiv admin note: text overlap with arXiv:2106.05471 by other authors