CSLs of the root lattice $\mathbf{A_4}$

TL;DR

This paper classifies all coincidence site lattices (CSLs) of the 4-dimensional root lattice A4, revealing new relations between isometries and CSLs using algebraic structures and generating functions.

Contribution

It provides a comprehensive classification of CSLs of A4, including criteria for when different isometries produce the same CSL, and introduces a Dirichlet series generating function for counting CSLs.

Findings

Identified conditions for isometries to generate identical CSLs

Derived explicit criteria using the icosian ring

Established a generating function for CSL counts

Abstract

Recently, the group of coincidence isometries of the root lattice $A_4$ has been determined providing a classification of these isometries with respect to their coincidence indices. A more difficult task is the classification of all CSLs, since different coincidence isometries may generate the same CSL. In contrast to the typical examples in dimensions $d \leq 3$, where coincidence isometries generating the same CSL can only differ by a symmetry operation, the situation is more involved in 4 dimensions. Here, we find coincidence isometries that are not related by a symmetry operation but nevertheless give rise to the same CSL. We indicate how the classification of CSLs can be obtained by making use of the icosian ring and provide explicit criteria for two isometries to generate the same CSL. Moreover, we determine the number of CSLs of a given index and encapsulate the result in a Dirichlet series generating function.