Walking, Weak first-order transitions, and Complex CFTs

TL;DR

This paper explores the concept of walking behavior and weak first-order phase transitions across different physical systems, revealing their common origin in complex fixed points called complex CFTs and discussing their implications for observable phenomena.

Contribution

It introduces the idea of complex CFTs as fixed points governing walking behavior and weak first-order transitions, providing a unified RG interpretation across systems.

Findings

Walking phenomena are linked to RG flows near complex fixed points.

Observables in walking theories can be computed via conformal perturbation theory.

The paper discusses the implications for 4D gauge theories and phase transition scenarios.

Abstract

We discuss walking behavior in gauge theories and 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. We discuss what distinguishes a real theory from a complex theory and call these fixed points complex CFTs. By using conformal perturbation theory we show how observables of the walking theory are computable by perturbing the complex CFTs. This paper discusses the general mechanism while a companion paper [1] will treat a specific and computable example: the two-dimensional Q-state Potts model with Q > 4. Concerning walking in 4d gauge theories, we also comment on the (un)likelihood of the light pseudo-dilaton, and on non-minimal scenarios of the conformal window termination.