Block-transitive t-(k^2,k,\lambda) designs associated to two dimensional projective special linear groups

Abstract

This paper investigates block-transitive automorphism groups of t-(k^2,k,\lambda) designs. Let D be a non-trivial t-(k^2,k,\lambda) design, G \leq \Aut(D) be block-transitive with X\unlhd G\leq \Aut(X), where X = PSL(2,q)(q\geq4). Then q = 8 and D is a 2-(36,6,\lambda) design with \lambda \in \{2,6,9,12,18,36\}.