Next-to-leading order numerical calculations in Coulomb gauge

Calculations of observables in quantum chromodynamics can be performed using a method in which all of the integrations, including integrations over virtual loop momenta, are performed numerically. We use the flexibility inherent in this method in order to perform next-to-leading order calculations for event shape variables in electron-positron annihilation in Coulomb gauge. The use of Coulomb gauge provides the potential to go beyond a purely order alpha_s^2 calculation by including, for instance, renormalon or parton showering effects. We expect that the approximations needed to include such effects at all orders in alpha_s will be simplest in a gauge in which unphysically polarized gluons do not propagate over long distances.Comment: 36 pages with 7 figure

B-meson decay constants from 2+1-flavor lattice QCD with domain-wall light quarks and relativistic heavy quarks

We calculate the B-meson decay constants fB, fBs, and their ratio in unquenched lattice QCD using domain-wall light quarks and relativistic b quarks. We use gauge-field ensembles generated by the RBC and UKQCD collaborations using the domain-wall fermion action and Iwasaki gauge action with three flavors of light dynamical quarks. We analyze data at two lattice spacings of a ~ 0.11, 0.086 fm with unitary pion masses as light as Mπ ~ 290 MeV; this enables us to control the extrapolation to the physical light-quark masses and continuum. For the b quarks we use the anisotropic clover action with the relativistic heavy-quark interpretation, such that discretization errors from the heavy-quark action are of the same size as from the light-quark sector. We renormalize the lattice heavy-light axial-vector current using a mostly nonperturbative method in which we compute the bulk of the matching factor nonperturbatively, with a small correction, that is close to unity, in lattice perturbation theory. We also improve the lattice heavy-light current through O (αsa). We extrapolate our results to the physical light-quark masses and continuum using SU(2) heavy-meson chiral perturbation theory, and provide a complete systematic error budget. We obtain fB0 = 199.5(12.6)  MeV, fB+ = 195.6(14.9)  MeV, fBs = 235.4(12.2)  MeV, fBs/fB0 = 1.197(50), and fBs/fB+ = 1.223(71), where the errors are statistical and total systematic added in quadrature. These results are in good agreement with other published results and provide an important independent cross-check of other three-flavor determinations of B-meson decay constants using staggered light quarks

First Nonperturbative Test of a Relativistic Heavy Quark Action in Quenched Lattice QCD

We perform a numerical test of a relativistic heavy quark(RHQ) action, recently proposed by Tsukuba group, in quenched lattice QCD at $a\simeq 0.1$ fm. With the use of the improvement parameters previously determined at one-loop level for the RHQ action, we investigate a restoration of rotational symmetry for heavy-heavy and heavy-light meson systems around the charm quark mass. We focused on two quantities, the meson dispersion relation and the pseudo-scalar meson decay constants. It is shown that the RHQ action significantly reduces the discretization errors due to the charm quark mass. We also calculate the S-state hyperfine splittings for the charmonium and charmed-strange mesons and the $D_s$ meson decay constant. The remaining discretization errors in the physical quantities are discussed.Comment: 21 pages, 16 figures. A reference and a comment added, a major modification in appendix, several minor changes in the abstract and the main text. Errors in affiliation are corrected. Version appeared in JHE

Status of and performance estimates for QCDOC

QCDOC is a supercomputer designed for high scalability at a low cost per node. We discuss the status of the project and provide performance estimates for large machines obtained from cycle accurate simulation of the QCDOC ASIC.Comment: 3 pages 1 figure. Lattice2002(machines

Instanton vibrations of the 3-Skyrmion

The Atiyah-Drinfeld-Hitchin-Manin matrix corresponding to a tetrahedrally symmetric 3-instanton is calculated. Some small variations of the matrix correspond to vibrations of the instanton-generated 3-Skyrmion. These vibrations are decomposed under tetrahedral symmetry and this decomposition is compared to previous knowledge of the 3-Skyrmion vibration spectrum.Comment: 10 pages, LaTeX, no figures, PRD version with longer introduction and minor change

Lagrangian Becchi-Rouet-Stora-Tyutin treatment of collective coordinates

The Becchi-Rouet-Stora-Tyutin (BRST) treatment for the quantization of collective coordinates is considered in the Lagrangian formalism. The motion of a particle in a Riemannian manifold is studied in the case when the classical solutions break a non-abelian global invariance of the action. Collective coordinates are introduced, and the resulting gauge theory is quantized in the BRST antifield formalism. The partition function is computed perturbatively to two-loops, and it is shown that the results are independent of gauge-fixing parameters.Comment: LaTeX file, 26 pages, PostScript figures at end of fil

Correlations in the Sine-Gordon Model with Finite Soliton Density

We study the sine-Gordon (SG) model at finite densities of the topological charge and small SG interaction constant, related to the one-dimensional Hubbard model near half-filling. Using the modified WKB approach, we find that the spectrum of the Gaussian fluctuations around the classical solution reproduces the results of the Bethe ansatz studies. The modification of the collective coordinate method allows us to write down the action, free from infra-red divergencies. The behaviour of the density-type correlation functions is non-trivial and we demonstrate the existence of leading and sub-leading asymptotes. A consistent definition of the charge-raising operator is discussed. The superconducting-type correlations are shown to decrease slowly at small soliton densities, while the spectral weight of right (left) moving fermions is spread over neighboring "4k_F" harmonics.Comment: 12 pages, 3 eps figures, REVTEX; a discussion of fermions is adde

Hardware and software status of QCDOC

QCDOC is a massively parallel supercomputer whose processing nodes are based on an application-specific integrated circuit (ASIC). This ASIC was custom-designed so that crucial lattice QCD kernels achieve an overall sustained performance of 50% on machines with several 10,000 nodes. This strong scalability, together with low power consumption and a price/performance ratio of $1 per sustained MFlops, enable QCDOC to attack the most demanding lattice QCD problems. The first ASICs became available in June of 2003, and the testing performed so far has shown all systems functioning according to specification. We review the hardware and software status of QCDOC and present performance figures obtained in real hardware as well as in simulation.Comment: Lattice2003(machine), 6 pages, 5 figure

Comments on Noncommutative ADHM Construction

We extend the method of matrix partition to obtain explicitly the gauge field for noncommutative ADHM construction in some general cases. As an application of this method we apply it to the U(2) 2-instanton and get explicit result for the gauge fields in the coincident instanton limit. We also easily apply it to the noncommutative 't Hooft instantons in the appendix.Comment: 17 pages, LaTeX; an appendix added, typos corrected, refs adde

On Instantons and Zero Modes of N=1/2 SYM Theory

We study zero modes of N=1/2 supersymmetric Yang-Mills action in the background of instantons. In this background, because of a quartic antichiral fermionic term in the action, the fermionic solutions of the equations of motion are not in general zero modes of the action. Hence, when there are fermionic solutions, the action is no longer minimized by instantons. By deforming the instanton equation in the presence of fermions, we write down the zero mode equations. The solutions satisfy the equations of motion, and saturate the BPS bound. The deformed instanton equations imply that the finite action solutions have U(1) connections which are not flat anymore.Comment: 9 pages, latex file, added references, minor change