# Slava Rychkov

“Walking, weakly first-order phase transitions, and complex CFTs”
Abstract:
Appetizer: Most people have heard that the 2d Potts model with Q=5 states has a first order phase transition, but not everyone knows that the correlation length at this phase transition is 2500 lattice spacings.
We will review “walking RG” behavior in gauge theories and connect it to Type II weak first-order phase transitions in statistical physics. Despite appearing in very different systems (QCD below the conformal window, the Potts model, deconfined criticality) these two phenomena both imply approximate scale invariance in a range of energies and have the same RG interpretation: a flow passing between pairs of fixed point at complex coupling, dubbed “complex CFTs”. Observables of the real walking theory are approximately computable by perturbing the complex CFTs. The general mechanism will be illustrated by a specific and computable example: the two-dimensional Q-state Potts model with Q > 4. Based on http://arxiv.org/abs/1807.11512 and http://arxiv.org/abs/1808.04380