Hadron Structure and the QCD Phase Transition

TL;DR

This paper reviews the current understanding of QCD near the critical temperature, focusing on hadron spectral changes during the chiral transition and discussing experimental detection methods.

Contribution

It provides a comprehensive review of QCD behavior near the phase transition, clarifies issues with sum rules at finite temperature/density, and summarizes experimental plans.

Findings

Spectral changes of hadrons in hot/dense media are significant.

Differences between Yukawa and Hagedorn regimes are emphasized.

Experimental strategies for detecting medium modifications are summarized.

Abstract

Firstly, I give a brief summary of the current understanding of QCD below and near $T_c$ (the critical temperature of the chiral transition). Some emphases are put on the qualitative difference between the Yukawa regime ($T \sim 0)$ and the Hagedorn regime ($T \sim T_c$). 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.