Characterization by forbidden induced subgraphs of some subclasses of chordal graphs

Abstract

Chordal graphs are the graphs in which every cycle of length at least four has a chord. A set S is a vertex separator for vertices a and b if the removal of S of the graph separates a and b into distinct connected components. A graph G is chordal if and only if every minimal vertex separator is a clique. We study subclasses of chordal graphs defined by restrictions imposed on the intersections of its minimal separator cliques. Our goal is to characterize them by forbidden induced subgraphs. Some of these classes have already been studied such as chordal graphs in which two minimal separators have no empty intersection if and only if they are equal. Those graphs are known as strictly chordal graphs and they were first introduced as block duplicate graphs by Golumbic and Peled [Golumbic, M. C. and Peled, U. N., Block duplicate graphs and a hierarchy of chordal graphs, Discrete Applied Mathematics, 124 (2002) 67–71], they were also considered in [Kennedy, W., “Strictly chordal graphs and phylogenetic roots”, Master Thesis, University of Alberta, 2005] and [De Caria, P. and Gutiérrez, M., On basic chordal graphs and some of its subclasses, Discrete Applied Mathematics, 210 (2016) 261–276], showing that strictly chordal graphs are exactly the (gem, dart)-free graphs.