Light-front field theory of hot and dense quark matter

Extending the concepts of light-front field theory to quantum statistics provides a novel approach towards nuclear matter under extreme conditions. Such conditions exist, e.g., in neutron stars or in the early stage of our universe. They are experimentally expected to occur in heavy ion collisions, e.g., at RHIC and accelerators to be build at GSI and CERN. Light-front field theory is particularly suited, since it is based on a relativistic Hamiltonian approach. It allows us to treat the perturbative as well as the nonperturbative regime of QCD and also correlations that emerge as a field of few-body physics and is important for hadronization. Last but not least the Hamiltonian approach is useful for nonequilibrium processes by utilizing, e.g., the formalism of nonequilibrium statistical operators.Comment: 6 pages, talk presented at Light-Cone 2004, Amsterdam, 16 - 20 Augus

Modeling emergent tissue organization involving high-speed migrating cells in a flow equilibrium

There is increasing interest in the analysis of biological tissue, its organization and its dynamics with the help of mathematical models. In the ideal case emergent properties on the tissue scale can be derived from the cellular scale. However, this has been achieved in rare examples only, in particular, when involving high-speed migration of cells. One major difficulty is the lack of a suitable multiscale simulation platform, which embeds reaction-diffusion of soluble substances, fast cell migration and mechanics, and, being of great importance in several tissue types, cell flow homeostasis. In this paper a step into this direction is presented by developing an agent-based mathematical model specifically designed to incorporate these features with special emphasis on high speed cell migration. Cells are represented as elastic spheres migrating on a substrate in lattice-free space. Their movement is regulated and guided by chemoattractants that can be derived from the substrate. The diffusion of chemoattractants is considered to be slower than cell migration and, thus, to be far from equilibrium. Tissue homeostasis is not achieved by the balance of growth and death but by a flow equilibrium of cells migrating in and out of the tissue under consideration. In this sense the number and the distribution of the cells in the tissue is a result of the model and not part of the assumptions. For purpose of demonstration of the model properties and functioning, the model is applied to a prominent example of tissue in a cellular flow equilibrium, the secondary lymphoid tissue. The experimental data on cell speed distributions in these tissues can be reproduced using reasonable mechanical parameters for the simulated cell migration in dense tissue.Comment: 27 pages, 7 figures v2 major conceptual changes: stronger focus on model architecture; new Fig 6, fitting of migration parameters; reduced Fig 7 (formerly Fig 6), shortened presentation of the application; equation (3) provided in more detail; Fig 5 extende

Quark Structure and Weak Decays of Heavy Mesons

We investigate the quark structure of D and B mesons in the framework of a constituent quark model. To this end, we assume a scalar confining and a one gluon exchange (OGE) potential. The parameters of the model are adopted to reproduce the meson mass spectrum. From a fit to ARGUS and CLEO data on B->D*lv semileptonic decay we find for the Cabbibo Kobayashi Maskawa matrix element Vcb=0.036+-0.003. We compare our form factors to the pole dominance hypothesis and the heavy quark limit. For non-leptonic decays we utilize factorization and for B->D*X decays we find a1 = 0.96+-0.05, and a2=0.31+-0.03.Comment: LATEX, 26 pages, 12 tables, 6 figures (appended as uuencoded file but also available as postscript files from the authors), BONN TK-93-1

Linear meson and baryon trajectories in AdS/QCD

An approximate holographic dual of QCD is constructed and shown to reproduce the empirical linear trajectories of universal slope on which the square masses of radially and orbitally excited hadrons join. Conformal symmetry breaking and other IR effects are described exclusively by deformations of the anti-de Sitter background metric. The predictions for the light hadron spectrum include new relations between ground state masses and trajectory slopes and are in good overall agreement with experimental data.Comment: 4 page