Stability anaylsis for k-wise intersecting families

Abstract

We consider the following generalization of the seminal Erdős-Ko-Rado theorem, due to Frankl. For some k>=2, let F be a k-wise intersecting family of r-subsets of an n element set X, i.e. for any k sets F1,...,Fk in F, their intersection is nonempty. If r <= ((k-1)n)/k, then |F|<= {n-1 \choose r-1}. We prove a stability version of this theorem, analogous to similar results of Dinur-Friedgut, Keevash-Mubayi and others for the Erdős-Ko-Rado theorem. The technique we use is a generalization of Katona's circle method, initially employed by Keevash, which uses expansion properties of a particular Cayley graph of the symmetric group.