Three regimes/phases of QCD at high T, their symmetries and N_c scaling

Abstract

We review recent developments on the QCD phase diagram at small chemical potentials and increasing temperature. There are three regimes/phases in QCD which differ by symmetries, degrees of freedom and N_c scaling: the hadron gas below the chiral restoration temperature T_ch, the stringy fluid between T_ch and the deconfinement temperature T_d and the quark-gluon plasma above T_d.

Comments: 5 double-column pages. Invited talk at (i) Exploring QCD matters at high temperatures and densities, BNL, February 2-4, 2026; (ii) 16th Workshop on critical point and onset of deconfinement, CERN, April 13-17, 2026; (iii) Buenas ideas on QCD phase diagram, Yukawa Institute, Kyoto, May 26-29, 2026