This paper is devoted to the study of 2-designs with λ≥(r,λ)2 admitting a flag-transitive automorphism group G. The group G has been shown to be point-primitive of either almost simple or affine type. In this paper, we classify the 2-designs with λ≥(r,λ)2>1 admitting a flag-transitive almost simple automorphism group with socle PSLn(q) or PSUn(q) for n≥3.
@article{arxiv.2511.14145,
title = {Flag-transitive $2$-$(v,k,\lambda)$ designs with $\lambda\ge (r,\lambda)^2$},
author = {Junchi Zhang and Jianbing Lu and Meizi Ou},
journal= {arXiv preprint arXiv:2511.14145},
year = {2025}
}