Difference sets satisfying the Deza Cayley graph parameter condition

Determine whether there exist difference sets in abelian groups, other than the known examples, with parameters $(v,k,\lambda)$ satisfying $k=\frac{2v-1-\sqrt{8v-7}}{2}$, so that the associated generalized dihedral Cayley graph is a strictly Deza graph.

Background

Proposition \ref{ds} characterizes when a nontrivial difference set RR in an abelian group AA yields a Deza Cayley graph Cay(G,RbA#)\operatorname{Cay}(G,Rb\cup A^\#) over the generalized dihedral group G=AbG=A\rtimes\langle b\rangle. The necessary and sufficient condition is k=2v18v72k=\frac{2v-1-\sqrt{8v-7}}{2}, and in that case the graph is strictly Deza.

The paper exhibits examples with parameters (7,3,1)(7,3,1), (11,6,3)(11,6,3), (16,10,6)(16,10,6), and (37,28,21)(37,28,21), producing several strictly Deza Cayley graphs. It then reports that database verification found no additional examples with v10000v\leq 10000, leaving open whether any other difference sets satisfy the required condition.

References

We do not know whether there exist other DSs satisfying the condition $k=\frac{2v-1-\sqrt{8v-7}}{2}$. Checking using the database of DSs implies that there is no other such a DS with $v\leq 10000$.

Deza Cayley graphs from difference sets  (2506.10440 - Ryabov, 12 Jun 2025) in Section 3.1, immediately following Corollary 3 (the corollary labeled \ref{dsgraphs})