Imaginary geometry III: reversibility of SLE_κ for κ\in (4,8)

Abstract

Suppose that D is a planar Jordan domain and x and y are distinct boundary points of D. Fix κ\in (4,8) and let η be an SLE_κprocess from x to y in D. We prove that the law of the time-reversal of ηis, up to reparameterization, an SLE_κprocess from y to x in D. More generally, we prove that SLE_κ(ρ_1;ρ_2) processes are reversible if and only if both ρ_i are at least κ/2-4, which is the critical threshold at or below which such curves are boundary filling. Our result supplies the missing ingredient needed to show that for all κ\in (4,8) the so-called conformal loop ensembles CLE_κ are canonically defined, with almost surely continuous loops. It also provides an interesting way to couple two Gaussian free fields (with different boundary conditions) so that their difference is piecewise constant and the boundaries between the constant regions are SLE_κcurves.