20187829
Calculation of the pion's quark distribution amplitude in lattice QCD with dynamical fermions.
We present a calculation of the pion decay constant and of the second moment of the quark distribution amplitude of the pion within full lattice QCD. Measurements are made on 12{sup 3}{times}24 and 16{sup 3}{times}32 lattices, using two flavors of Wilson fermion. Different methods used to extract {ital f}{sub {pi}} give consistent results. We find a better signal for the second moment of the distribution amplitude than in previous lattice calculations and obtain results that are significantly smaller than those obtained from sum-rule calculations and previously in (quenched) lattice QCD.
18442234
Comparison of Inversion Algorithms for Wilson Fermions on the CM5
This talk presents results of a comparitive study of iterative algorithms like minimal residue ($MR$) and conjugate gradient ($CG$, $BiCG\gamma_5$, and \bicgstab) used for inverting the Dirac matrix $M$. The tests were done on the Connection Machine CM-5 using $32^3 \times 64$ lattices. The fermion action used is of Wilson type, both with and without the clover term. The overall conclusion is that preconditioned over-relaxed $MR$ is the simplest, uses the least memory, and is comparable in performance to \bicgstab. We find these two algorithms to be equally robust, $i.e.$ insensitive to the starting solution and to round-off errors.
122633786
Monte Carlo Renormalization Group: A Review
The logic and the methods of Monte Carlo Renormalization Group (MCRG) are reviewed. A status report of results for 4-dimensional lattice gauge theories derived using MCRG is presented. Existing methods for calculating the improved action are reviewed and evaluated. The Gupta-Cordery improved MCRG method is described and compared with the standard one.
15540297
Chiral limit of QCD
This talk contains an analysis of quenched chiral perturbation theory and its consequences. The chiral behavior of a number of quantities such as the pion mass m{sub pi}{sup 2}, the Bernard-Golterman ratios R and {sub X}, the masses of nucleons, and the kaon B-parameter are examined to see if the singular terms induced by the additional Goldstone boson, {eta}{prime}, are visible in present data. The overall conclusion (different from that presented at the lattice meeting) of this analysis is that even though there are some caveats attached to the indications of the extra terms induced by {eta}{prime} loops, the standard expressions break down when extrapolating the quenched data with m{sub q} < m{sub s}/2 to physical light quarks. I then show that due to the single and double poles in the quenched {eta}{prime}, the axial charge of the proton cannot be calculated using the Adler-Bell-Jackiw anomaly condition. I conclude with a review of the status of the calculation of light quark masses from lattice QCD.
121903104
Simulating QCD with dynamical Wilson and staggered fermions
Abstract I present a summary of the work done during the last year by the Los Alamos lattice collaboration (C. Baillie, R. Gupta, G. Kilcup, G. Guralnik, A. Patel and S. Sharpe) to study QCD with the Hybrid Monte Carlo Algorithm. The specific questions we have addressed are the finite temperature transition for both staggered and Wilson fermions and screening in the heavy q q potential with Wilson fermions. I also present a discussion of the efficiency of the fermion update algorithm.
124910471
Monte Carlo Renormalization Group for SU(2) Lattice Gauge Theory
We present the results of a Monte Carlo renormalization group calculation using the ..sqrt..3 block transformation introduced by Cordery, Gupta, and Novotny. The ..beta.. function for the SU(2) lattice gauge theory is calculated both along the Wilson axis and along the line K/sub A/ = -0.24K/sub F/ in the fundamental-adjoint plane.
27549292
Isoscalar axial-vector renormalization constant and polarized proton structure function.
The isoscalar axial-vector renormalization constant is reevaluated using the QCD sum-rule method. It is found to be substantially different from the anomaly-free octet axial-vector u¯γμγ5+d¯γμγ5-2s¯γμγ5 coupling. Combining this determination with the known values of the isovector coupling GA and the F/D ratio for the octet current, we find the integral of the polarized proton structure function to be Gp=Fgp1(x)dx=0.135, in agreement with recent measurement by the European Muon Collaboration.
32229676
Precision description of the octet-baryon magnetic moments.
Addition of an SU(3) (flavor)-tensor term having isoscalar and isovector parts to the quark-model expressions reduces the chi/sup 2/ per degree of freedom to 1.28 from 80 for the recent precision magnetic-moment data of the octet baryons. The isospin symmetry is well obeyed as the ratio of the magnetic moment of the down quark to that of the up quark is -0.499.
40514876
Hadronic correlation functions in the QCD plasma phase.
We present results for static hadronic correlation functions in the high-temperature phase of QCD with four flavors of dynamical quarks. We confirm chiral-symmetry restoration through the degeneracies of the spectrum of screening lengths. We also find that the screening lengths for the {rho} and {ital N} channels at {ital T}{approx gt}1.2{ital T}{sub {ital c}} are close to that in a free quark gas.
43411058
Semirelativistic potential model for heavy quarkonia.
The c-italicc-bar, b-italicb-bar, and t-italic t-italic-bar spectra are investigated with the use of a semirelativistic potential model described in an earlier paper. Results for the energy levels, leptonic widths, and E-italic1 transition widths are compared with the experimental data for c-italicc-bar and b-italicb-bar and predicted for t-italic t-italic-bar. We also find that the quark-antiquark interaction can best be described by a quasistatic rather than a momentum-dependent potential, and propose a theoretical justification for this surprising conclusion.
7265145
Quark mixing and CP violation.
In view of the experimental indications that the top-quark mass may exceed the upper bound predicted by the Fritzsch ansatz for the quark mass matrices, we follow a phenomenological approach to find a modified form of the mass matrices to deal with quark mixing and {ital CP} violation in electroweak interactions. The essential feature of our mass matrices is that the diagonal elements corresponding to the light quarks {ital u}, {ital d}, and {ital s} are vanishingly small, while those corresponding to the heavy quarks {ital c}, {ital b}, and {ital t} are approximately equal to the observed values of their masses. By comparing our theoretical results for the Kobayashi-Maskawa mixing matrix elements with the experimental data, we obtain for the top-quark mass and the {ital CP}-violating phase the values {ital m}{sub {ital t}}{sup phys}{le}170 GeV and 91{degree}{le}{delta}{le}105{degree}.