Hadron Structure and the QCD Phase Transition

Firstly, I give a brief summary of the current understanding of QCD below and near Tc (the critical temperature of the chiral transition). Some emphases are put on the qualitative difference between the Yukawa regime (T ∼ 0) and the Hagedorn regime (T ∼ Tc). Secondly, the dynamical phenomena associated with the chiral transition, in particular, the spectral changes of hadrons in hot and/or dense medium are reviewed from the point of view of the QCD spectral sum rules. Confusions on the QCD sum rules at finite temperature/density are also clarified and remarks on the effective lagrangian approaches are given. Thirdly, planned experiments to detect the spectral changes in medium are summarized. 1 Invited talk at the 9-th Nishinomiya Yukawa-Memorial Symposium on Theoretical Physics, (Oct. 27-28, 1994, Nishinomiya, Japan) e-mail address: [email protected]