About Me
Cosmology
Rocks
QFT and Gauge Fields
Publications
Supercomputing
The Cosmic Data Arxiv
Cosmology Lunch
Nonequilibrium Quantum Field Theories and Gauge Theories
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Nonequilibrium dynamics have become a very active field of research in the last few years in nearly all parts of physics. In condensed matter physics for example the description of the dynamics of nonequilibrium phase transitions plays an important role. Such phase transitions occur in ferromagnets, superfluids, and liquid crystals to name only a few. They are subjects of intensive studies, both theoretical and experimental. Also in cosmology some phenomena require the use of nonequilibrium technics. One example is the electroweak phase transition which took place 10^{-12} seconds after the Big Bang. If the electroweak phase transition is a phase transition of first order then it leads to a possibility to explain the observed asymmetry between matter and anti-matter. The mechanism which is responsible for the asymmetry is called baryogenesis. Another phenomenon in cosmology where nonequilibrium dynamics are important is the inflationary phase of the early universe. Inflation refers to an epoch during the evolution of the Universe in which it underwent an accelerated expansion phase. This would resolve some of the short comings of the Standard hot Big Bang model, e.g., the flatness problem, concerning the energy density of the universe and the horizon problem, related by the large scale smoothness of the universe, indicated by the Cosmic Microwave Background Radiation (CMBR). At lower energies heavy ion collisions are under consideration as nonequilibrium processes. In such heavy ion collisions a new state of matter could be reached if the short range impulsive forces between nucleons could be overcome and if squeezed nucleons would merge into each other. This new state should be a Quark Gluon Plasma (QGP), in which quarks and gluons, the fundamental constituents of matter, are no longer confined, but free to move around over a volume in which a high enough temperature and/or density reveals. Heavy ion collisions are studied experimentally at current and forthcoming accelerators, the Relativistic Heavy Ion Collider RHIC at Brookhaven and the Large Hadron Collider LHC at CERN. The occurring Quantum Chromodynamic (QCD) phase transition in these processes could be out of equilibrium and lead to formations of coherent condensates of low energy pions, so called Disoriented Chiral Condensates (DCC). So there are many good reasons to study quantum field theories out of equilibrium. During my graduate studies and my first two years as a postdoc in Los Alamos I have worked mainly in this area. Together with Jurgen Baacke and Carsten Patzold I developed a new renormalization scheme for nonequilibrium field theories which allowed us to extract the divergent contributions from the theory explicitly using dimensional regularization. This method has the great advantage that a numerical implementation of the equation of motions of the system is then possible on a "normal desktop". Even when I joined Los Alamos and got access to supercomputers, I did not change my opion that this is a very useful achievement!! :-) Together with my collaborators I studied different models and approximations, including gauge theories, supersymmetric theories, the one-loop approximation, and the large-N approximation. The study of gauge theories, and specifically the question of gauge invariance, i.e., how to make sure that my results do not depend on the choice of the gauge, occupied a large fraction of my time. Gauge field theories are an important part for elementary particle physics and cosmology (and got a few people the Noble Prize!). They successfully describe the strong interactions of quarks and the weak forces of quark and leptons. If we ever want to understand the qurk-gluon plasma really deeply, we have to be able to understand gauge fields out-of-equilibrium. In the left corner you can see one of the vertices which had to be taken into account for the renormalization of the gauge theory: Phi is the background field, h is a qunatum fluctuation, and the other two quantum fluctuations are the gauge fluctuations.Publications
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