Non-solvable groups whose character degree graph has a cut-vertex. III

Abstract

Let G be a finite group. Denoting by $$\textrm{cd}(G)$$ cd ( G ) the set of the degrees of the irreducible complex characters of G, we consider the character degree graph of G: this, is the (simple, undirected) graph whose vertices are the prime divisors of the numbers in $$\textrm{cd}(G)$$ cd ( G ) , and two distinct vertices p, q are adjacent if and only if pq divides some number in $$\textrm{cd}(G)$$ cd ( G ) . This paper completes the classification, started in Dolfi et al. (Non-solvable groups whose character degree graph has a cut-vertex. II, 2022. https://doi.org/10.1007/s10231-022-01299-3) and Dolfi et al. (Non-solvable groups whose character degree graph has a cut-vertex. I, 2022. https://doi.org/10.48550/arXiv.2207.10119), of the finite non-solvable groups whose character degree graph has a cut-vertex, i.e., a vertex whose removal increases the number of connected components of the graph. More specifically, it was proved in Dolfi et al. (Non-solvable groups whose character degree graph has a cut-vertex. I, 2022. https://doi.org/10.48550/arXiv.2207.10119 that these groups have a unique non-solvable composition factor S, and that S is isomorphic to a group belonging to a restricted list of non-abelian simple groups. In Dolfi et al. (Non-solvable groups whose character degree graph has a cut-vertex. II, 2022. https://doi.org/10.1007/s10231-022-01299-3) and Dolfi et al. (Non-solvable groups whose character degree graph has a cut-vertex. I, 2022. https://doi.org/10.48550/arXiv.2207.10119) all isomorphism types for S were treated, except the case $$S\cong \textrm{PSL}_{2}(2^a)$$ S ≅ PSL 2 ( 2 a ) for some integer $$a\ge 2$$ a ≥ 2 ; the remaining case is addressed in the present paper.