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The overpopulated Quark Gluon Plasma on the Lattice

Subject Area Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
Term from 2013 to 2017
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 233033195
 
Final Report Year 2016

Final Report Abstract

The project aimed at computing the nonequilibrium real-time dynamics of quantum fields in extreme conditions, which concerns one of the most pressing issues in the physics of relativistic heavy-ion collisions and is of great relevance for the physics of the early universe. The real-time problem can be addressed using lattice techniques in the limit of very large collision energy. Our work represents one of the largest calculational efforts ever done in this respect. The analytical and numerical techniques that had to be applied and further developed cover a wide range of most sophisticated tools in strongly correlated many-body physics out of equilibrium. Performing these calculations, one of the central outcomes concerns the answer to a long-standing question: We discovered that the space-time evolution of the logitudinally expanding non-Abelian plasma in the weak-coupling limit exhibits self-similar dynamics. In particular, we were able to show that this solution singles out a specific thermalization scenario: the ``bottom-up’’ framework proposed by Baier, Müller, Schiff and Son. Since different scenarios had been proposed based on parametric estimates in the literature, this is the first time that a determination from first principles was achieved. These results are also used now as a crucial input in state-of-the-art kinetic descriptions, which continue the evolution to later times, such as employed recently by Kurkela and co-workers. An intriguing new research direction also arises from the discovery of universality far from equilibrium, which allows one to study important aspects of the early-time gauge dynamics by mappings to simpler scalar field theories in the same universality class. The works on fermion dynamics on real-time lattices gave important first quantitative insights into fermion-antifermion pair production far from equilibrium, and provide the technological basis for several new research directions (such as photon production from nonequilibrium plasmas and the impact of quantum anomalies). Practically all the research objectives that were put forward in the original proposal have been addressed, except for the study of nonequilibrium dynamics at non-zero baryon number density, which is in view of the reduced funding that was granted still a very successful outcome. The project was also essential as preparatory work for the recently established Collaborative Research Center “Isolated quantum systems and universality in extreme conditions” (ISOQUANT SFB 1225).

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