Molecules of an affine FPF $W$-graph and a labelled row-Beissinger reconstruction

Abstract

Kazhdan--Lusztig $W$-graphs encode the cell structure of Hecke algebras, while their bidirected connected components are called molecules. In finite type~$A$, the Robinson--Schensted correspondence describes cells and molecules, and Beissinger's row insertion constructs the common tableau associated with an involution. In affine type~$A$, the affine matrix-ball construction (AMBC) assigns an affine permutation a pair of tabloids together with a dominant weight, and Marberg introduced affine fixed-point-free (FPF) $W$-graphs indexed by affine FPF involutions. We classify and enumerate the molecules of Marberg's $\m$-type affine FPF $W$-graph $Γ_n^{\m}$ and show that molecules with the same AMBC shape have isomorphic underlying simple bidirected graphs. We also prove that labelled complete-cycle row-Beissinger truncations recover the full AMBC datum of an affine FPF involution.