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Hartmut Wittig

Publications and source records attributed to Hartmut Wittig.

At least 145 records · Page 8Linked to original sources
arXiv2002

Panel discussion on chiral extrapolation of physical observables

This is an approximate reconstruction of the panel discussion on chiral extrapolation of physical observables. The session consisted of brief presentations from panelists, followed by responses from the panel, and concluded with questions and comments from the floor with answers from panelists. In the following, the panelists have summarized their statements, and the ensuing discussion has been approximately reconstructed from notes.

hep-lat↗
arXiv2002

Fundamental parameters of QCD

The theory of strong interactions, QCD, is described in terms of a few parameters, namely the strong coupling constant alpha_s and the quark masses. We show how these parameters can be determined reliably using computer simulations of QCD on a space-time lattice, and by employing a finite-size scaling method, which allows to trace the energy dependence of alpha_s and quark masses over several orders of magnitude. We also discuss methods designed to reduce the effects of finite lattice spacing and address the issue of computer resources required.

physics.comp-ph↗
arXiv2001

Scalar condensate and light quark masses from overlap fermions

We have studied pseudoscalar correlation functions computed using the overlap operator. Within the accuracy of our calculation we find that the quark mass dependence agrees with the prediction of lowest-order Chiral Perturbation Theory (ChPT) for quark masses in the range of m ~ m_s/2-2m_s. We present the results of an analysis which assumes lowest-order ChPT to be valid to extract the low-energy constants Sigma and f_P, as well as the strange quark mass. Non-perturbative renormalization is implemented via a matching procedure with data obtained using Wilson fermions in the Schroedinger functional set-up. We find that the scalar condensate computed here agrees with the one obtained previously through a finite-size scaling analysis.

hep-lat↗
arXiv2001

Non-perturbative renormalization of the quark condensate in Ginsparg-Wilson regularizations

We present a method to compute non-perturbatively the renormalization constant of the scalar density for Ginsparg-Wilson fermions. It relies on chiral symmetry and is based on a matching of renormalization group invariant masses at fixed pseudoscalar meson mass, making use of results previously obtained by the ALPHA Collaboration for O(a)-improved Wilson fermions. Our approach is quite general and enables the renormalization of scalar and pseudoscalar densities in lattice regularizations that preserve chiral symmetry and of fermion masses in any regularization. As an application we compute the non-perturbative factor which relates the renormalization group invariant quark condensate to its bare counterpart, obtained with overlap fermions at beta=5.85 in the quenched approximation.

hep-lat↗
arXiv2001

First results on the running coupling in QCD with two massless flavours

We report on the non-perturbative computation of the running coupling of two-flavour QCD in the Schr"odinger functional scheme. The corresponding Lambda-parameter, which describes the coupling strength at high energy, is related to a low energy scale which still remains to be connected to a hadronic ``experimentally'' observable quantity. We find the non-perturbative evolution of the coupling indispensable to avoid untolerable errors in the estimated Lambda-parameter.

hep-lat↗
arXiv2000

Strangeness in Lattice QCD

The status of lattice calculations in the light hadron sector is reviewed. Special emphasis is given to recent lattice determinations of the mass of the strange quark. The impact of non-perturbative renormalization and control over lattice artefacts on the attainable precision is discussed in detail. Furthermore the influence of dynamical quark effects is assessed.

hep-ph↗
arXiv2000

Effective Chiral Lagrangians and Lattice QCD

We propose a general method to obtain accurate estimates for some of the "low-energy constants" in the one-loop effective chiral Lagrangian by means of simulating lattice QCD. In particular, the method is sensitive to those constants whose values are required to test the hypothesis of a massless up-quark. Initial tests performed in the quenched approximation confirm that good statistical precision can be achieved. As a byproduct we obtain an accurate estimate for the ratio of pseudoscalar decay constants, F_K/F_pi, in the quenched approximation, which lies 10% below the experimental result. The quantities that serve to extract the low-energy constants also allow a test of the scaling behaviour of different discretizations of QCD and a search for the effects of dynamical quarks.

hep-lat↗
arXiv2000

Non-perturbative quark mass renormalization in quenched lattice QCD

The renormalization factor relating the bare to the renormalization group invariant quark masses is accurately calculated in quenched lattice QCD using a recursive finite-size technique. The result is presented in the form of a product of a universal factor times another factor, which depends on the details of the lattice theory but is easy to compute, since it does not involve any large scale differences. As a byproduct the Lambda-parameter of the theory is obtained with a total error of 8%.

hep-lat↗
arXiv1999

Lattice Gauge Theory

The status of lattice calculations in Quantum Field Theory is reviewed. A major part is devoted to recent progress in formulating exact chiral symmetry on the lattice. Another topic which has received a lot of attention is the influence of dynamical quark effects. Attempts to quantify these effects for the light hadron spectrum and flavour singlet amplitudes are discussed, as well as other expected qualitative features of simulations with dynamical quarks. The remaining parts of the review include recent results for the light quark masses using non-perturbative renormalisation and the spectrum of glueballs and heavy hybrids computed using anisotropic lattices.

hep-ph↗
arXiv1999

Low energy physics from the QCD Schrödinger functional

We review recent work by the ALPHA and UKQCD Collaborations where masses and matrix elements were computed in lattice QCD using Schrödinger functional boundary conditions and where the strange quark mass was determined in the quenched approximation. We emphasize the general concepts and our strategy for the computation of quark masses.

hep-lat↗
arXiv1999

Precision computation of the strange quark's mass in quenched QCD

We determine the renormalization group invariant quark mass corresponding to the sum of the strange and the average light quark mass in the quenched approximation of QCD, using as essential input the mass of the K-mesons. In the continuum limit we find $(M_s + M_{light})/F_K=0.874(29)$, which includes systematic errors. Translating this non-perturbative result into the running quark masses in the $\msbar$-scheme at $μ=2 GeV$ and using the quark mass ratios from chiral perturbation theory, we obtain $\mbar_s(2 GeV)=97(4) MeV$. With the help of recent results by the CP-PACS Collaboration, we estimate that a 10% higher value would be obtained if one replaced $F_K$ by the nucleon mass to set the scale. This is a typical ambiguity in the quenched approximation.

hep-lat↗
arXiv1999

Hadron masses and matrix elements from the QCD Schr"odinger functional

We explain how masses and matrix elements can be computed in lattice QCD using Schr"odinger functional boundary conditions. Numerical results in the quenched approximation demonstrate that good precision can be achieved. For a statistical sample of the same size, our hadron masses have a precision similar to what is achieved with standard methods, but for the computation of matrix elements such as the pseudoscalar decay constant the Schr"odinger functional technique turns out to be much more efficient than the known alternatives.

hep-lat↗
arXiv1999

String Breaking in SU(2) Yang Mills Theory with Adjoint Sources

We compute the static potential in three-dimensional SU(2) Yang Mills Theory with adjoint sources using numerical simulations. By employing a variational approach involving string and gluelump operators, we obtain clear evidence for string breaking in the adjoint potential. The breaking scale r_b is computed and extrapolated to the continuum limit. The result in units of the scalar glueball mass is r_b*m_G = 10.3 +/- 1.5. We also resolve the structure of higher excitations of the flux-tube and gluelumps. Furthermore we discuss the implications of our findings for the case of the four-dimensional theory.

hep-lat↗
arXiv1997

Verification of O(a) improvement

The status of simulations using the non-perturbatively O(a) improved Wilson action in the quenched approximation is reviewed. The impact of non-perturbative improvement on the hadronic mass spectrum and the size of residual lattice artefacts in spectral quantities and decay constants are assessed.

hep-lat↗
arXiv1997

Leptonic Decays of Heavy Quarks on the Lattice

The status of lattice calculations of heavy-light decay constants and of the $B$ parameter $B_B$ is reviewed. After describing the lattice approach to heavy quark systems, the main results are discussed, with special emphasis on the systematic errors in present lattice calculations. A detailed analysis of the continuum limit for decay constants is performed. The implications of lattice results on studies of CP violation in the Standard Model are discussed.

hep-lat↗
arXiv1996

Non-perturbative determination of the axial current normalization constant in O(a) improved lattice QCD

A finite-size technique is employed to compute the normalization constant $Z_A$ of the isovector axial current in lattice QCD. The calculation is carried out in the quenched approximation for values of the bare gauge coupling $g_0$ ranging from 0 to 1. In the lattice action and the lattice expression for the axial current we include the counterterms required for O(a) improvement, with non-perturbatively determined coefficients. With little additional work the normalization constant $Z_V$ of the improved isospin current is also obtained.

hep-lat↗
arXiv1996

Status and Prospects for Lattice Calculations in Heavy Quark Physics

The current status of lattice calculation of weak matrix elements for heavy quark systems is reviewed. After an assessment of systematic errors in present simulations, results for the B meson decay constant, the B-parameter B_B and semi-leptonic heavy-to-light and heavy-to-heavy transitions are discussed. The final topic are lattice results for heavy baryon spectroscopy.

hep-ph↗