Topological transitions in the euclidean 2d U(1)-Higgs model

The two-dimensional U(1)-gauged Higgs model is studied on an euclidean lattice of size $L_1\times L_2$, where the temperature $T=L_2^{-1}$ is of the order of the sphaleron mass. The simulation parameters are taken from zero temperature results. By comparison with classical and semiclassical results I discuss, whether the sphaleron transition rate can be extracted from the behavior of the Chern-Simons number and from the formation of vortices in an euclidean simulation at high temperatures.Comment: Talk presented at LATTICE96(topology), 3 pages, latex2e, 3 postscript figures, uses packages epsfig and espcrc

Calculation of the renormalized charmed-quark mass in Lattice QCD

The correlator of heavy-quark currents is calculated in quenched Lattice QCD on a $16^3 \times 32$-lattice for $\beta= { 6, 6.3 }$. The renormalized charmed quark mass is extracted from the short-distance part of that correlator: $m_c^{\overline{MS}}(m_c) = 1.22(5) GeV$. We study the sensitivity of our data to the strong coupling constant.Comment: 3 pages, LaTeX plus Postscript files of figures and the style-files. Contribution to the Proceedings of LAT9

Sphaleron transitions in a realistic heat bath

We measure the diffusion rate of Chern-Simons number in the (1+1)-dimensional Abelian Higgs model interacting with a realistic heat bath for temperatures between 1/13 and 1/3 times the sphaleron energy. It is found that the measured rate is close to that predicted by one-loop calculation at the lower end of the temperature range considered but falls at least an orderof magnitude short of one-loop estimate at the upper end of that range. We show numerically that the sphaleron approximation breaks down as soon as the gauge-invariant two-point function yields correlation length close to the sphaleron size.Comment: 13 pages, LATeX + 3 figures included as postscript files, to be encapsulated using epsf. Also available as a compressed postscript file by anonymous ftp from maggia.ethz.ch (login ftp, pw ftp; then: cd pub, binary, get sphb.ps.Z). IPS Research Report No. 93-1

Sphaleron transition rate at high temperature in the 1+1 D abelian Higgs model

New results for the rate are presented using the canonical ensemble in the classical approximation on a spatial lattice. We find that the rate at high temperatures is proportional to $T^2$, and strongly dependent on the lattice spacing $a$. We conclude that a better effective action is needed for the classical approximation.Comment: 3 pages, uuencoded compressed postscript file, contribution to the Conference Proceedings "LATTICE 94", Bielefeld- German