Which chiral symmetry is restored in hot QCD?

Abstract

We review the current status of the problem of chiral symmetry restoration, discussing an open question of whether at the $SU(N_f{)}_A$ restoration point $T=T_c$ the $U(1{)}_A$ chiral symmetry is or is not (approximately) restored. New lattice and instanton-based studies are considered, and some new calculations are suggested to clarify the issue. We also speculate on possible experimental manifestations of two possible scenarios.