Fusions of the tensor product of a strongly regular graph

Allen Herman¹ ; Neha Joshi²

¹University of Regina
²Arizona State University

The electronic journal of combinatorics, Tome 32 (2025) no. 2

Résumé

In this article we determine all fusions of the association scheme $\mathcal{A} \otimes \mathcal{A}$, where $\mathcal{A}$ is the symmetric rank $3$ association scheme corresponding to a strongly regular graph. This includes both guaranteed fusions, which are fusions for all symmetric rank $3$ association schemes $\mathcal{A}$, and specific case fusions, which exist only under restrictions on the parameters of the association scheme. Along the sections we will determine the fusions of wreath products of strongly regular graphs and the fusions of the tensor square of a symmetric rank $3$ table algebra. This is an extension to the recent work of the authors and Meagher, where we solved the same problem for the generalized Hamming scheme $H(2,\mathcal{A})$ of the association scheme obtained from a strongly regular graph. The main results of this article prove that the families of strongly regular graphs for which $\mathcal{A} \otimes \mathcal{A}$ has a special case fusion are the same families for which $H(2,\mathcal{A})$ has a special case fusion; and that the imprimitive strongly regular graphs are the only family of strongly regular graphs for which the wreath product $\mathcal{A} \wr \mathcal{A}$ has a special case fusion.

Détail

DOI : 10.37236/13380

Classification : 05E30, 05C25
Mots-clés : association scheme, fusions of wreath products of strongly regular graphs, generalized Hamming scheme