Possibility of Spontaneous Parity Violation in Hot QCD

We argue that for QCD in the limit of a large number of colors, the axial $\mathrm{U}(1)$ symmetry of massless quarks is effectively restored at the deconfining phase transition. If this transition is of second order, metastable states in which parity is spontaneously broken can appear in the hadronic phase. These metastable states have dramatic signatures, including enhanced production of $\ensuremath{\eta}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}$ mesons, which can decay through parity violating decay processes such as $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$, and global parity odd asymmetries for charged pions.