MATTER UNDER EXTREME CONDITIONS

We study scenarios for chiral symmetry restoration and deconfinement a t finite temperature and/or density, based on assuming universal scali ng relations for some hadron masses. We explore and discuss consequenc es of this scaling assumption in nuclear structure and show that most experiments support the scaling. The relevance of soft and hard scales as pertaining to chiral symmetry restoration and deconfinement is emp hasized, and scaling relations for nonstrange and strange Goldstone bo sons are presented. Theoretical support for the scaling relations is f ound from the analysis of effective Lagrangians in hot and dense matte r, as well as finite-temperature and finite-density QCD sum rules. Bot h approaches suggest the validity of approximate scaling relations and identify sources of violation of the latter. Finite-temperature hadro n masses can be compared to the results of QCD lattice gauge calculati ons. We show that large screening masses above T(c) merging into chira l multiplets are consistent with thermal, rather then dynamically gene rated, quark masses on the lattice. The results are consistent with va nishing dynamically generated masses above T(c), where T(c) is interpr eted as the chiral symmetry restoration temperature. We review the ''d ynamical confinement'' scenario of hot quarks and show that the hadron ic wavefunctions obtained above T(c) are consistent with those obtaine d from recent measurements of the latter in lattice QCD. This suggests that there are strong quark/antiquark correlations in the vector meso n channels. We conclude that for finite-temperature QCD, chiral symmet ry above T(c) is realized in terms of essentially massless multiplets of chiral partners, and that chiral symmetry restoration is the only p hase transition.