Quantum chromodynamics extreme

Quantenchromodynamics, the fundamental theory of the nuclear forces in terms of never directly observed quarks and gluons, has been studied at extreme temperatures and densities by means of collider experiments using heavy ions. These experiments have produced evidence for a new form of matter, the quark-gluon plasma, with surprisingly strong collective behavior that cannot be accounted for by conventional methods. Methods deriving from superstring theory, using a holographic description of gauge theories at high temperatures by means of 5- dimensional geometries with imbedded black holes, have been successfully applied for modelling a strongly coupled quark-gluon plasma. With the new accelerator LHC at CERN, heavy-ion collision experiments will soon probe substantially higher energies where the transition to an essentially weakly coupled quark-gluon plasma might be observed. The latter holds the promise of new collective effects such as non-Abelian plasma instabilities. The aim of this project will be to study equilibrium and non-equilibrium features of the quark-gluon plasma for both strongly and weakly coupled quark- gluon plasmas and their respective characteristics.

Quantenchromodynamics, the fundamental theory of the nuclear forces in terms of never directly observed quarks and gluons, has been studied at extreme temperatures and densities by means of collider experiments using heavy ions. These experiments have produced evidence for a new form of matter, the quark-gluon plasma, with surprisingly strong collective behaviour that cannot be accounted for by conventional methods. Methods deriving from superstring theory, using a holographic description of gauge theories at high temperatures by means of 5-dimensional geometries with imbedded black holes, have been successfully applied for modelling a strongly coupled quark-gluon plasma. With the new accelerator LHC at CERN, heavy-ion collision experiments are now probing substantially higher energies which allow the theoretical descriptions to be tested. This permits to address also astrophysical questions such as the nature of matter in the interior of neutron stars, which might be dense enough to involve quark matter instead of ordinary nuclear matter. In both, heavy-ion collisions and some neutron stars, it is known that extremely strong magnetic fields are present, leading to novel effects for the structure of the extremely dense matter. One of the topics of this research project was the analysis of these effects. The so-called chiral magnetic effect, which was discovered a few years ago and which predicts a separation of charged particles in a quark-gluon plasma, was reproduced in 5-dimensional descriptions in agreement with experimental observations. For strongly magnetized neutron stars (so-called magnetars), a new effect was found, called inverse magnetic catalysis, which has important consequences for the phase structure of quark and nuclear matter.Another central topic was the analysis of non-equilibrium phenomena in heavy-ion collisions, for which 5-dimensional descriptions were developed. These indicate a surprising reduction of viscosity in an anisotropic quark-gluon plasma, leading to a violation of a previously conjectured lowest value for viscosity of strongly coupled quantum fluids and thus a new record for this physical parameter. Numerous other properties were evaluated with the new string-theoretic methods and compared to numerical simulations of anisotropic quark-gluon plasma using supercomputer facilities. In the coming years, these can be tested in heavy-ion collisions at CERN at even higher energies than already achieved.