A quasi-stability result for dictatorships in $S_{n}$

TL;DR

This paper establishes a quasi-stability result for certain Boolean functions on the symmetric group, showing they are close to unions of cosets of point-stabilizers, with applications to intersecting families and isoperimetric inequalities.

Contribution

It introduces a new quasi-stability theorem for Boolean functions on $S_n$ based on Fourier concentration, providing natural proofs for existing stability results.

Findings

Boolean functions with Fourier concentration are close to unions of cosets

Proves a stability result for intersecting families of permutations

Establishes a quasi-stability result for edge-isoperimetric inequalities in $S_n$

Abstract

We prove that Boolean functions on $S_{n}$ whose Fourier transform is highly concentrated on the first two irreducible representations of $S_n$, are close to being unions of cosets of point-stabilizers. We use this to give a natural proof of a stability result on intersecting families of permutations, originally conjectured by Cameron and Ku, and first proved by the first author. We also use it to prove a `quasi-stability' result for an edge-isoperimetric inequality in the transposition graph on $S_n$, namely that subsets of $S_n$ with small edge-boundary in the transposition graph are close to being unions of cosets of point-stabilizers.