We study four-point functions of critical percolation in two dimensions, and
more generally of the Potts model. We propose an exact ansatz for the spectrum:
an infinite, discrete and non-diagonal combination of representations of the
Virasoro algebra. Based on this ansatz, we compute four-point functions using a
numerical conformal bootstrap approach. The results agree with Monte-Carlo
computations of connectivities of random clusters.Comment: 16 pages, Python code available at
https://github.com/ribault/bootstrap-2d-Python, v2: some clarifications and
minor improvement
