Gliding down the QCD transition line, from $N_f=2$ till the onset of conformality

Understand

We review the hot QCD transition with varying number of flavors, from two till the onset of the conformal window.

• We discuss the universality class for $N_f=2$, along the critical line for two massless light flavors, and a third flavor whose mass serves as an interpolator between $N_f = 2$ and $N_f=3$.
• We identify a possible scaling window for the 3D $O(4)$ universality class transition, and its crossover to a mean field behaviour.
• We follow the transition from $N_f=3$ to larger $N_f$, when it remains of first order, with an increasing coupling strength; we summarize its known properties, including possible cosmological applications as a model for a strong electroweak transition.