Does hot QCD have a conformal manifold in the chiral limit?

TL;DR

This paper investigates the nature of the chiral phase transition in hot QCD, proposing a conformal manifold of universality classes influenced by baryon density, constrained by anomaly considerations.

Contribution

It introduces a novel conformal manifold scenario for the critical line in hot QCD, extending beyond traditional Ginzburg-Landau descriptions, supported by anomaly constraints.

Findings

Lattice evidence suggests a second-order chiral transition for Nf ≥ 2.

An 't Hooft anomaly constrains the critical line at all baryon chemical potentials.

Proposes a conformal manifold with an exactly marginal operator related to baryon density.

Abstract

Recent lattice evidence suggests the chiral phase transition in QCD is second-order for $N_f \ge 2$ massless flavors. We constrain CFT descriptions of a critical line in temperature $T$ and imaginary baryon chemical potential $\theta_B = i\mu_B/T$. An 't Hooft anomaly at general $\theta_B$ constrains the transition even at $\theta_B = 0$, leaving only three minimal scenarios. The best-motivated scenario for $N_f\ge3$, and perhaps also $N_f = 2$, is beyond Ginzburg-Landau, featuring a conformal manifold of $\theta_B$-dependent universality classes with an exactly marginal operator related to baryon density.