Hadrons in Hot and Dense Matter

The description of excitations in hot and dense (hadronic) matter is discussed with emphasis on the use of correlation functions as a common framework for comparing different model (and QCD lattice) calculations with each other. Typical regimes of applicability of hadronic approaches are assessed, together with possibilities to confront them with experiment. We also elaborate on recent developments to relate baryonic in-medium effects to chiral symmetry restoration.Comment: Convener Talk at the Int. Conf. on Quark Nuclear Physics, June 9-14, 2002 (Juelich, Germany); 3 pages LaTeX including 5 eps-figures and EPJ style file

Comprehensive Interpretation of Thermal Dileptons at the SPS

Employing thermal dilepton rates based on medium-modified electromagnetic correlation functions we show that recent dimuon spectra of the NA60 collaboration in central In-In collisions at the CERN-SPS can be understood in terms of radiation from a hot and dense hadronic medium. Earlier calculated \rho-meson spectral functions, as following from hadronic many-body theory, provide an accurate description of the data up to dimuon invariant masses of about M\simeq 0.9 GeV, with good sensitivity to details of the predicted \rho-meson line shape. This, in particular, identifies baryon-induced effects as the prevalent ones. We show that a reliable description of the \rho contribution opens the possibility to study further medium effects: at higher masses (M \simeq 0.9-1.5 GeV) 4-pion type annihilation is required to account for the experimentally observed excess indicating precursor effects of chiral symmetry restoration (``chiral mixing''), while remaining structures in the \omega and \phi region are suggestive for modifications in their line shapes as well.Comment: 4 pages, 4 figures, v2: slightly improved estimate of four-pion contributions; accepted for publication in Phys. Rev. Let

Identifying Word Translations in Non-Parallel Texts

Common algorithms for sentence and word-alignment allow the automatic identification of word translations from parallel texts. This study suggests that the identification of word translations should also be possible with non-parallel and even unrelated texts. The method proposed is based on the assumption that there is a correlation between the patterns of word co-occurrences in texts of different languages.Comment: 3 pages, requires aclap.sty and epic.st

Vector Mesons in Medium and Dileptons in Heavy-Ion Collisions

Theoretical approaches to assess modifications of vector mesons in the medium, as well as their experimental identification via electromagnetic probes, are discussed. Implications for the nature of chiral symmetry restoration in hot/dense matter are outlined and put into context with the axialvector channel.Comment: Invited talk by first author at the 2nd KEK-Tanashi International Symposium on 'Nuclear and Hadronic Physics with Electromagnetic Probes', Tokyo, Oct. 25-27, 1999; 8 pages LaTeX including 7 eps-figures and style file espcrc1.st

Duality and Chiral Restoration from Dilepton Production in Relativistic Heavy-Ion Collisions

We discuss the recent status in the theoretical understanding of dilepton production in central heavy-ion reactions with the Pb-beam at the full CERN-SpS energy of 158 AGeV. In the low-mass region ($M\le$~1 GeV) a strong broadening of the vector meson resonances in hot and dense matter (especially for the $\rho$ meson) entails thermal dilepton rates very reminiscent to perturbative $q\bar q$ annihilation close to the expected phase boundary of the chiral symmetry restoring transition. A consistent description of the experimentally observed enhancement at both low and intermediate masses (1.5 GeV~$\le M \le$~3 GeV) in terms of thermal radiation from an expanding fireball can be obtained.Comment: Talk given at ISMD '99 on 'QCD & Multiparticle Production' (Brown University, Providence, Aug. 9-13), 7 pages LaTeX including 6 ps-/eps-figures and sprocl.st