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Permutation graphs and the abelian sandpile model, tiered trees and non-ambiguous binary trees. (English) Zbl 1418.05051

Summary: A permutation graph is a graph whose edges are given by inversions of a permutation. We study the Abelian sandpile model (ASM) on such graphs. We exhibit a bijection between recurrent configurations of the ASM on permutation graphs and the tiered trees introduced by W. Dugan et al. [J. Comb. Theory, Ser. A 164, 24–49 (2019; Zbl 1407.05048)]. This bijection allows certain parameters of the recurrent configurations to be read on the corresponding tree. In particular, we show that the level of a recurrent configuration can be interpreted as the external activity of the corresponding tree, so that the bijection exhibited provides a new proof of a famous result linking the level polynomial of the ASM to the ubiquitous Tutte polynomial. We show that the set of minimal recurrent configurations is in bijection with the set of complete non-ambiguous binary trees introduced by J.-C. Aval et al. [Adv. Appl. Math. 56, 78–108 (2014; Zbl 1300.05127)], and introduce a multi-rooted generalization of these that we show to correspond to all recurrent configurations. In the case of permutations with a single descent, we recover some results from the case of Ferrers graphs presented in [M. Dukes et al., Eur. J. Comb. 81, 221–241 (2019; Zbl 1419.05008)], while we also recover results of D. Perkinson et al. [Combinatorica 37, No. 2, 269–282 (2017; Zbl 1399.05006)] in the case of threshold graphs.

MSC:

05C05 Trees
82C20 Dynamic lattice systems (kinetic Ising, etc.) and systems on graphs in time-dependent statistical mechanics

Software:

OEIS

Online Encyclopedia of Integer Sequences:

Sum_{n>=0} a(n)*x^n/n!^2 = -log(BesselJ(0,2*sqrt(x))).

References:

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