We study chiral symmetry restoration by analyzing thermal properties of QCD's
(pseudo-)Goldstone bosons, especially the pion. The meson properties are
obtained from the spectral densities of mesonic imaginary-time correlation
functions. To obtain the correlation functions, we solve the Dyson-Schwinger
equations and the inhomogeneous Bethe-Salpeter equations in the leading
symmetry-preserving rainbow-ladder approximation. In the chiral limit, the pion
and its partner sigma degenerate at the critical temperature Tcβ. At Tβ³Tcβ, it is found that the pion rapidly dissociates, which signals
deconfinement phase transition. Beyond the chiral limit, the pion dissociation
temperature can be used to define the pseudo-critical temperature of chiral
phase crossover, which is consistent with that obtained by the maximum point of
the chiral susceptibility. The parallel analysis for kaon and pseudoscalar
ssΛ suggests that heavy mesons may survive above Tcβ