Topological structure of the SU(3) vacuum and exceptional eigenmodes of the improved Wilson-Dirac operator

We present a study of the instanton size and spatial distributions in pure SU(3) gauge theory using under-relaxed cooling. We also investigate the low-lying eigenmodes of the (improved) Wilson-Dirac operator, in particular, the appearance of zero-modes and their space-time localisation with respect to instantons in the underlying gauge field.Comment: Contribution to Lattice97 proceedings: 3 pages, LaTeX2e, 4 postscript figures, uses espcrc2.st

Low-Lying Eigenvalues of the Wilson-Dirac Operator

An exploratory study of the low-lying eigenvalues of the Wilson-Dirac operator and their corresonding eigenvectors is presented. Results for the eigenvalues from quenched and unquenched simulations are discussed. The eigenvectors are studied with respect to their localization properties in the quenched approximation for the cases of SU(2) and SU(3).Comment: Poster presented at LATTICE96(poster). 4 pages, LaTeX, fully coloured versions of Figs. 4 and 5 are included as separate gzipped PostScript files or can be obtained from http://www.desy.de/library/cgi-bin/showprep.pl?desy-rep%2F199615

CP Violation and Strong Phases from Penguins in B±→VV\bf B^{\pm}\rightarrow VV Decays

We calculate direct CP-violating observables in charged $B\to VV$ decays arising from the interference of amplitudes with different strong and CKM phases. The perturbative strong phases develop at order $\alpha_s$ from absorptive parts of one-loop matrix elements of the next-to-leading logarithm corrected effective Hamiltonian. CPT constraints are maintained. Based on this model, we find that partial rate asymmetries between charge conjugate $B^{\pm}$ decays can be as high as 15-30\% for certain channels with branching ratios in the $10^{-6}$ range. The small values of the coefficients of angular correlations, which we calculated previously to be of order $10^{-2}$, are not significantly degraded by the strong phases. The charge asymmetries of rates and angular distributions would provide unambiguous evidence for direct CP violation.Comment: 24 pages, 3 figures (upon request), LaTeX, preprint DESY 93-19

Dynamical Simulations of Lattice QCD

Lattice calculations of Quantum Chromodynamics (QCD) are continuously becoming more realistic. Where Ukawa famously concluded only fourteen years ago that simulations including two physically light sea quarks are basically impossible even with today’s computers, algorithmic developments over the last years have changed this situation drastically. Nowadays up and down quark masses light enough to control the chiral extrapolation reliably are standard and also the sea quark effects of strange (and charm) quark are included.Modern lattice simulations are an intricate interplay between a large variety of numerical methods on one side and the computer hardware on the other side. The main areas of progress have been the solvers used for the Dirac equation, fermion determinant factorisations and better integrators for the molecular dynamics which is at the heart of most algorithms used for QCD simulations.In lattice QCD simulations the path integral is computed via a Markov Chain Monte Carlo method. In virtually all projects with dynamical fermions a variant of the Hybrid Monte Carlo algorithm is employed to generate the Markov chain, where the fields are updated using molecular dynamics. But there is considerable freedom in how to include the fermion determinant into the simulation. Factorisations of this determinant have been essential in the progress of recent years, being successful in particular together with improved integrators of the molecular dynamics.The solution of the Dirac equation constitutes the most computer time consuming element of simulations with fermions. The dramatic speedup for small fermion mass due to locally deflated solvers5, 6 has therefore had a significant impact on what is possible in the simulations. These algorithms have practically eliminated the increase in cost of the solution as the quark mass is lowered

The strong coupling from a nonperturbative determination of the Λ\Lambda parameter in three-flavor QCD

We present a lattice determination of the $\Lambda$ parameter in three-flavor QCD and the strong coupling at the Z pole mass. Computing the nonperturbative running of the coupling in the range from $0.2\,$GeV to $70\,$GeV, and using experimental input values for the masses and decay constants of the pion and the kaon, we obtain $\Lambda_{\overline{\rm MS}}^{(3)}=341(12)\,$MeV. The nonperturbative running up to very high energies guarantees that systematic effects associated with perturbation theory are well under control. Using the four-loop prediction for $\Lambda_{\overline{\rm MS}}^{(5)}/\Lambda_{\overline{\rm MS}}^{(3)}$ yields $\alpha^{(5)}_{\overline{\rm MS}}(m_{\rm Z}) = 0.11852(84)$.Comment: Correction in the comparison to the LHC value for alpha(1.5TeV) which was given by CMS in the 5-flavor theory. The agreement is improved. Also 1 Reference added and a few typos correcte

The Λ\Lambda-parameter in 3-flavour QCD and αs(mZ)\alpha_s(m_Z) by the ALPHA collaboration

We present results by the ALPHA collaboration for the $\Lambda$-parameter in 3-flavour QCD and the strong coupling constant at the electroweak scale, $\alpha_s(m_Z)$, in terms of hadronic quantities computed on the CLS gauge configurations. The first part of this proceedings contribution contains a review of published material \cite{Brida:2016flw,DallaBrida:2016kgh} and yields the $\Lambda$-parameter in units of a low energy scale, $1/L_{\rm had}$. We then discuss how to determine this scale in physical units from experimental data for the pion and kaon decay constants. We obtain $\Lambda_{\overline{\rm MS}}^{(3)} = 332(14)$ MeV which translates to $\alpha_s(M_Z)=0.1179(10)(2)$ using perturbation theory to match between 3-, 4- and 5-flavour QCD.Comment: 21 pages. Collects contributions of A. Ramos, S. Sint and R. Sommer to the 34th annual International Symposium on Lattice Field Theory; LaTeX input encoding problem fixe

A new simulation algorithm for lattice QCD with dynamical quarks

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.Comment: 7 pages, postscript file (166 KB

B-physics with Nf=2N_f=2 Wilson fermions

We report the final results of the ALPHA collaboration for some B-physics observables: $f_B$, $f_{B_s}$ and $m_b$. We employ CLS configurations with 2 flavors of $O(a)$ improved Wilson fermions in the sea and pion masses ranging down to 190 MeV. The b-quark is treated in HQET to order $1/m_b$. The renormalization, the matching and the improvement were performed non-perturbatively, and three lattice spacings reaching $a=0.048$ fm are used in the continuum extrapolation

Decay constants of B-mesons from non-perturbative HQET with two light dynamical quarks

We present a computation of B-meson decay constants from lattice QCD simulations within the framework of Heavy Quark Effective Theory for the b-quark. The next-to-leading order corrections in the HQET expansion are included non-perturbatively. Based on Nf=2 gauge field ensembles, covering three lattice spacings a (0.08-0.05)fm and pion masses down to 190MeV, a variational method for extracting hadronic matrix elements is used to keep systematic errors under control. In addition we perform a careful autocorrelation analysis in the extrapolation to the continuum and to the physical pion mass limits. Our final results read fB=186(13)MeV, fBs=224(14)MeV and fBs/fB=1.203(65). A comparison with other results in the literature does not reveal a dependence on the number of dynamical quarks, and effects from truncating HQET appear to be negligible.Comment: 16 pages including figures and table

The b-quark mass from non-perturbative Nf=2N_f=2 Heavy Quark Effective Theory at O(1/mh)O(1/m_h)

We report our final estimate of the b-quark mass from $N_f=2$ lattice QCD simulations using Heavy Quark Effective Theory non-perturbatively matched to QCD at $O(1/m_h)$. Treating systematic and statistical errors in a conservative manner, we obtain $\overline{m}_{\rm b}^{\overline{\rm MS}}(2 {\rm GeV})=4.88(15)$ GeV after an extrapolation to the physical point.Comment: 15 pages including figures and tables; as published in Phys.Lett.B / typo in table 4 corrected / footnote 1 expande