Four-Loop Decoupling Relations for the Strong Coupling

We compute the matching relation for the strong coupling constant within the framework of QCD up to four-loop order. This allows a consistent five-loop running (once the $\beta$ function is available to this order) taking into account threshold effects. As a side product we obtain the effective coupling of a Higgs boson to gluons with five-loop accuracy.Comment: 11 page

Understanding Confinement From Deconfinement

We use effective magnetic SU(N) pure gauge theory with cutoff M and fixed gauge coupling g_m to calculate non-perturbative magnetic properties of the deconfined phase of SU(N) Yang-Mills theory. We obtain the response to an external closed loop of electric current by reinterpreting and regulating the calculation of the one loop effective potential in Yang-Mills theory. This effective potential gives rise to a color magnetic charge density, the counterpart in the deconfined phase of color magnetic currents introduced in effective dual superconductor theories of the confined phase via magnetically charged Higgs fields. The resulting spatial Wilson loop has area law behavior. Using values of M and g_m determined in the confined phase, we find SU(3) spatial string tensions compatible with lattice simulations in the temperature interval 1.5T_c < T < 2.5T_c. Use of the effective theory to analyze experiments on heavy ion collisions will provide applications and further tests of these ideas.Comment: 18 pages, 5 figures, v2: fixed archive title (only

Ground states versus low-temperature equilibria in random field Ising chains

We discuss with the aid of random walk arguments and exact numerical computations the magnetization properties of one-dimensional random field chains. The ground state structure is explained in terms of absorbing and non-absorbing random walk excursions. At low temperatures, the magnetization profiles follow those of the ground states except at regions where a local random field fluctuation makes thermal excitations feasible. This follows also from the non-absorbing random walks, and implies that the magnetization length scale is a product of these two scales. It is not simply given by the Imry-Ma-like ground state domain size nor by the scale of the thermal excitations.Comment: 7 pages LaTeX, 8 eps-figures include

The warm circumstellar envelope and wind of the G9 IIb star HR 6902

IUE observations of the eclipsing binary system HR 6902 obtained at various epochs spread over four years indicate the presence of warm circumstellar material enveloping the G9 IIb primary. The spectra show Si IV and C IV absorption up to a distance of 3.3 giant radii (R_g}. Line ratio diagnostics yields an electron temperature of ~ 78000 K which appears to be constant over the observed height range. Applying a least square fit absorption line analysis we derive column densities as a function of height. We find that the inner envelope (< 3 R_g) of the bright giant is consistent with a hydrostatic density distribution. The derived line broadening velocity of ~ 70 kms^{-1} is sufficient to provide turbulent pressure support for the required scale height. However, an improved agreement with observations over the whole height regime including the emission line region is obtained with an outflow model. We demonstrate that the common beta power-law as well as a P \propto rho wind yield appropriate fit models. Adopting a continuous mass outflow we obtain a mass-loss rate of M_loss= (0.8 - 3.4)*10^{-11} M_{sun}yr^{-1} depending on the particular wind model.Comment: 11 pages, 8 figures, submitted to Astronomy Astrophysics main Journa

Numerical simulation of inductive heating processes

For product optimization regarding weight reduction, material properties have to be adapted efficiently. To achieve this, new compositions of materials can be created or the manufacturing process can be changed in a way that heterogeneous distributions of material properties are enabled. An example for such an improved process chain is the production of thermo-mechanically graded structures like shafts. The manufacturing method mainly consists of three stages. The first one is characterized by a local temperature increase of the workpiece due to inductive heating. In the second phase the workpiece is deformed and simultaneously cooled throughout the contact with the forming die. In the last step, however, a high pressured air stream is applied, leading to a partial cooling of the workpiece. The inductive heating step is controlled by an alternating current inducing a high frequency magnetic field, which causes a temperature increase due to the resulting eddy currents. To analyse this process, the coupling between the electric and the magnetic field is described by the fully coupled Maxwell equations. Moreover the heat conduction equation is considered to describe thermal effects. To solve this multifield the equations are in the first step decoupled using an additional time differentiation. In the second step an axisymmetric case is considered, motivated by the fact that the inductive heating process of a cylindrical shaft is analysed. Afterwards the resulting equations are spatially discretized by the Galerkin finite element method. The temporal discretization is carried out via the Newmark method so that afterwards the electrical source distribution can be achieved. As a consequence the temperature evolution is determined in a postprocessing step

Four-Loop Tadpoles: Applications in QCD

Recent applications of single-scale four-loop tadpoles are briefly reviewed. An algorithm for the evaluation of current correlators based on differential equations is described and applied to obtain high moments of the vacuum polarization function at O(alphas^2) as a preparation of O(alphas^3) calculations.Comment: 5 pages, 1 figure, to appear in the proceedings of the 8th DESY Workshop on Elementary Particle Theory, Loops and Legs in Quantum Field Theory, April 23-28, 2006, Eisenach, German