Role of axial-vector mesons near the chiral phase transition

We present a systematic study of the vector–axial-vector mixing (V-A mixing) in the current correlation functions and its evolution with temperature within an effective field theory. The $a_1$-$\rho$-$\pi$ coupling vanishes at the critical temperature $T_c$ and thus the V-A mixing also vanishes. A remarkable observation is that even for finite $m_{\pi }$ the $\rho$ and $a_1$ meson masses are almost degenerate at $T_c$. The vanishing V-A mixing at $T_c$ stays approximately intact.