arXiv subjects
Publications and source records attributed to B. Jegerlehner.
We use simulations of heavy quark effective field theory to calculate the Isgur-Wise function, and we demonstrate the feasibility of calculating the matrix element for the $B \to π+ \leptons$ decay in the lattice heavy quark effective theory (HQET).
We present a general method to construct multiple mass solvers from standard algorithms. As an example, the BiCGstab-M algorithm is derived.
We investigate the application of Krylov space methods to the solution of shifted linear systems of the form (A+σ) x - b = 0 for several values of σsimultaneously, using only as many matrix-vector operations as the solution of a single system requires. We find a suitable description of the problem, allowing us to understand known algorithms in a common framework and developing shifted methods basing on short recurrence methods, most notably the CG and the BiCGstab solvers. The convergence properties of these shifted solvers are well understood and the derivation of other shifted solvers is easily possible. The application of these methods to quark propagator calculations in quenched QCD using Wilson and Clover fermions is discussed and numerical examples in this framework are presented. With the shifted CG method an optimal algorithm for staggered fermions is available.
We report on several improvements of the local bosonic algorithm proposed by M. Luescher. We find that preconditioning and over-relaxation works very well. A detailed comparison between the bosonic and the Kramers-algorithms shows comparable performance for the physical situation examined.
We study the impact of neutrino oscillations on the interpretation of the supernova (SN) 1987A neutrino signal by means of a maximum-likelihood analysis. We focus on oscillations between $\overlineν_e$ with $\overlineν_μ$ or $\overlineν_τ$ with those mixing parameters that would solve the solar neutrino problem. For the small-angle MSW solution ($Δm^2\approx10^{-5}\,\rm eV^2$, $\sin^22Θ_0\approx0.007$), there are no significant oscillation effects on the Kelvin-Helmholtz cooling signal; we confirm previous best-fit values for the neutron-star binding energy and average spectral $\overlineν_e$ temperature. There is only marginal overlap between the upper end of the 95.4\% CL inferred range of $\langle E_{\overlineν_e}\rangle$ and the lower end of the range of theoretical predictions. Any admixture of the stiffer $\overlineν_μ$ spectrum by oscillations aggravates the conflict between experimentally inferred and theoretically predicted spectral properties. For mixing parameters in the neighborhood of the large-angle MSW solution ($Δm^2\approx10^{-5}\,\rm eV^2$, $\sin^22Θ_0\approx0.7$) the oscillations in the SN are adiabatic, but one needs to include the regeneration effect in the Earth which causes the Kamiokande and IMB detectors to observe different $\overlineν_e$ spectra. For the solar vacuum solution ($Δm^2\approx10^{-10}\,\rm eV^2$, $\sin^22Θ_0\approx1$) the oscillations in the SN are nonadiabatic; vacuum oscillations take place between the SN and the detector. If either of the large-angle solutions were borne out by the upcoming round of solar neutrino experiments, one would have to conclude that the SN~1987A $\overlineν_μ$ and/or $\overlineν_e$ spectra had been much softer than predicted by current
First results on the autocorrelation behaviour of a recently proposed fermion algorithm by M. Lüscher are presented and discussed. The occurence of unexpected large autocorrelation times is explained. Possible improvements are discussed.
A previously introduced multi-boson technique for the simulation of QCD with dynamical quarks is described and some results of first test runs on a $6^3\times12$ lattice with Wilson quarks and gauge group SU(2) are reported.