Affine Wa(A4), Quaternions, and Decagonal Quasicrystals

TL;DR

This paper introduces a projection technique onto the Coxeter plane for higher dimensional lattices, demonstrating models for decagonal quasicrystals and revising quaternionic descriptions of related lattices.

Contribution

It presents a novel projection method onto Coxeter planes for higher-dimensional lattices and applies it to model decagonal quasicrystals, extending quaternionic lattice descriptions.

Findings

Projections of root and weight lattices onto Coxeter planes model decagonal quasicrystals.

Decomposition of affine Wa(A4) crystal spaces into orthogonal spaces with dihedral symmetry.

Voronoi cell projections reveal nested decagram structures related to the golden ratio.

Abstract

We introduce a technique of projection onto the Coxeter plane of an arbitrary higher dimensional lattice described by the affine Coxeter group. The Coxeter plane is determined by the simple roots of the Coxeter graph I2 (h) where h is the Coxeter number of the Coxeter group W(G) which embeds the dihedral group Dh of order 2h as a maximal subgroup. As a simple application we demonstrate projections of the root and weight lattices of A4 onto the Coxeter plane using the strip (canonical) projection method. We show that the crystal spaces of the affine Wa(A4) can be decomposed into two orthogonal spaces whose point groups is the dihedral group D5 which acts in both spaces faithfully. The strip projections of the root and weight lattices can be taken as models for the decagonal quasicrystals. The paper also revises the quaternionic descriptions of the root and weight lattices, described by the affine Coxeter group Wa(A3), which correspond to the face centered cubic (fcc) lattice and body centered cubic (bcc) lattice respectively. Extensions of these lattices to higher dimensions lead to the root and weight lattices of the group Wa(An), n>=4 . We also note that the projection of the Voronoi cell of the root lattice of Wa(A4) describes a framework of nested decagram growing with the power of the golden ratio recently discovered in the Islamic arts.