Comments on the U(1) axial symmetry and the chiral transition in QCD

Abstract

We analyze (using a chiral effective Lagrangian model) the scalar and pseudoscalar meson mass spectrum of QCD at finite temperature, above the chiral transition at $T_c$, looking, in particular, for signatures of a possible breaking of the $U(1)$ axial symmetry above $T_c$. A detailed comparison between the case with a number of light quark flavors $N_f\geq 3$ and the (remarkably different) case $N_f=2$ is performed.