# Connection probabilities for conformal loop ensembles

## TL;DR

This paper derives explicit connection probabilities for conformal loop ensembles (CLE) with various boundary conditions, linking these probabilities to parameters of related statistical physics models and building on advanced SLE and CLE theory.

## Contribution

It provides a formula for connection probabilities in CLE with boundary conditions, connecting CLE parameters to discrete model limits and utilizing advanced SLE and CLE properties.

## Key findings

- Connection probability for wired sides in a conformal square is 1/(1 - 2 cos(4π/κ)).
- Connection probabilities relate CLE parameters to N in O(N) models and q in FK percolation.
- Results build on SLE commutation relations and CLE properties related to Brownian loops and Gaussian free field.

## Abstract

The goal of the present paper is to explain, based on properties of the conformal loop ensembles CLE$_\kappa$ (both with simple and non-simple loops, i.e., for the whole range $\kappa \in (8/3, 8)$) how to derive the connection probabilities in conformal rectangles for a conditioned version of CLE$_\kappa$ which can be interpreted as a CLE$_{\kappa}$ with wired/free/wired/free boundary conditions on four boundary arcs (the wired parts being viewed as portions of to-be-completed loops). In particular, in the case of a conformal square, we prove that the probability that the two wired sides hook up so that they create one single loop is equal to $1/(1 - 2 \cos (4 \pi / \kappa ))$. Comparing this with the corresponding connection probabilities for discrete O(N) models for instance indicates that if a dilute O(N) model (respectively a critical FK(q)-percolation model on the square lattice) has a non-trivial conformally invariant scaling limit, then necessarily this scaling limit is CLE$_\kappa$ where $\kappa$ is the value in $(8/3, 4]$ such that $-2 \cos (4 \pi / \kappa )$ is equal to $N$ (resp. the value in $[4,8)$ such that $-2 \cos (4\pi / \kappa)$ is equal to $\sqrt {q}$). Our arguments and computations build on the one hand on Dub\'edat's SLE commutation relations (as developed and used by Dub\'edat, Zhan or Bauer-Bernard-Kyt\"ol\"a) and on the other hand, on the construction and properties of the conformal loop ensembles and their relation to Brownian loop-soups, restriction measures, and the Gaussian free field, as recently derived in works with Sheffield and with Qian.