Mon·Sep 26, 2005Monday·September 26, 2005

1. 01*

   3-flavour lattice QCD at finite density and temperature: QCD at finite isospin density revisited

   J.B.Kogut🇺🇸 · D.K.Sinclair🇺🇸

   We simulate 3-flavour lattice QCD at finite temperature and isospin chemical potential ${\mu }_I$. In particular we study the nature of the finite temperature transition for quark masses close to the critical mass at which this transition for zero chemical potentials changes from a first order transition to a crossover. We find that the Binder cumulants, used to determine the position of this transition, have very strong dt dependence. This leads us to an estimate of the critical mass which is about 20% below previous estimates. In addition, when this dt dependence is taken into account, we find that the Binder cumulants show very little dependence on mu_I. From this we conclude that we do not as yet see any evidence for the expected critical endpoint. We have argued previously that the position and nature of the finite temperature transition for small mu_I should be the same as that for small quark-number chemical potential mu.

   hep-lat8 citations
2. 02*

   Is there a third-order phase transition in quenched QCD?

   L. Li🇺🇸 · Y. Meurice🇺🇸

   We discuss the connection between the contributions of large field configurations and the large order behavior of perturbation theory. For quenched QCD, the sensitivity of the average plaquette to a removal of large field configurations has a narrow peak near beta=5.6. Various analysis of the order 10 weak coupling series for the plaquette give robust indications for a singularity in the third derivative of the free energy (second derivative of the plaquette) with respect to beta, near beta = 5.7. We report results of numerical calculations. The peak in the third derivative of the free energy present on 4^4 lattices disappears if the size of the lattice is increased isotropically up to a 10^4 lattice. On the other hand, on 4xL^3 lattices, it persists when L increases. The location of the peak coincides with the onset of a non-zero average for the Polyakov loop and seems related to the finite temperature transition. We also discuss the discrepancy between the perturbative series and the numerical values of the plaquette.

   hep-latPoS(2006)·1 citation
3. 03*

   Lattice simulations of Born-Infeld non-linear QED

   D.K.Sinclair🇺🇸 · J.B.Kogut🇺🇸

   Born-Infeld non-linear electrodynamics was introduced to render the self energy of a point particle finite. It has recently been revived as a field theory for branes and strings. We quantize this theory on a Euclidean space-time lattice, using Metropolis Monte-Carlo simulations to measure the properties of the quantum field theory. Luscher-Weisz methods are used to measure the electromagnetic fields from a static point charge. The D field from a point charge appears to be identical to that for the normal Maxwell Lagrangian. The E field is enhanced by quantum fluctuations, and shows short distance screening as it does in the classical theory.

   hep-lathep-thPoS(2006)·2 citations
4. 04*

   Maximal twist and the spectrum of quenched twisted mass lattice QCD

   Abdou M. Abdel-Rehim🇨🇦 · Randy Lewis🇨🇦 · R. M. Woloshyn🇨🇦

   Results on the hadron masses for a degenerate doublet of up and down quarks from quenched twisted mass lattice QCD at maximal twist are presented. Two definitions of maximal twist are used and the hadron masses for these definitions are compared. Mass splittings within the Delta(1232) multiplet due to flavor breaking effects are discussed.

   hep-latPoS(2006)·2 citations
5. 05*

   Scaling test of the P4-improved staggered fermion action

   Michael Cheng (for the RBC-Bielefeld Collaboration)🇺🇸

   We present a scaling study of the QCD spectrum using a smeared P4 staggered fermion formulation, in which three, five, and seven-link staples are added to reduce the effects of flavor symmetry breaking. These studies are performed on quenched lattices generated using the one-loop improved Symanzik gauge action, with Beta=10/g^2=7.40,7.75,8.00. The corresponding lattice spacings are a = .31 fm, .21 fm, and .14 fm. Particularly, we study the O(a^2) flavor symmetry violations in the pion spectrum as well as the scaling dependence of m_rho, measured in physical units, on lattice spacing. These results are compared against previous results for the Asqtad action.

   hep-latPoS(2006)·3 citations
6. 06*

   What we are learning about the Quark Structure of Hadrons from Lattice QCD?

   J. W. Negele🇺🇸

   Developments in lattice field theory and computer technology have led to dramatic advances in the use of lattice QCD to explore the quark structure of hadrons. This talk will describe selected examples, including structure functions, electromagnetic form factors, the nucleon axial charge, the origin of the nucleon spin, the transverse structure of the nucleon, and the nucleon to Delta transition form factor.

   hep-lat1 citation
7. 07*

   Hadron Structure from Lattice QCD

   LHPC collaboration: B. Bistrovic🇺🇸 · R. G. Edwards🇺🇸 · G. Fleming🇺🇸 · Ph. Hagler🇩🇪 · J. W. Negele🇺🇸 · K. Orginos🇺🇸 · A. Pochinsky🇺🇸 · D. B. Renner🇺🇸 · D. G. Richards🇺🇸 · W. Schroers🇩🇪

   The structure of neutrons, protons, and other strongly interacting particles is now being calculated in full, unquenched lattice QCD with quark masses entering the chiral regime. This talk describes selected examples, including the nucleon axial charge, structure functions, electromagnetic form factors, the origin of the nucleon spin, the transverse structure of the nucleon, and the nucleon to Delta transition form factor.

   hep-latInt.J.Mod.Phys.A(2006)·9 citations
8. 08*

   The Quark Structure of Pentaquarks

   O. Jahn🇺🇸 · J. W. Negele🇺🇸 · D. Sigaev🇺🇸

   Motivated by the possible observation of the ${\Theta }^{+}(1530)$, we study the quark structure of pentaquark states in quenched lattice QCD. The complete set of 19 local sources that have the proper symmetry for positive or negative parity isoscalar pentaquarks is constructed, as well as a nonlocal source composed of two displaced ``good'' diquarks. Quantitative structure information is determined from diagonalizing the 19-dimensional correlation matrix and from calculating the overlaps of sources with the lattice eigenstates. The volume dependence of the overlap is studied to differentiate between scattering and localized resonant states. The positive parity state has a small component of two ``good'' diquarks, and its energy is too much higher than the negative parity state to be a candidate for the ${\Theta }^{+}(1530)$.

   hep-latPoS(2006)·7 citations
9. 09*

   Performance of machines for lattice QCD simulations

   Tilo Wettig🇩🇪

   We review the architecture of massively parallel machines used for lattice QCD simulations and present benchmarks for the performance of popular algorithms on these platforms. We cover commercial supercomputers, PC clusters, and custom-designed machines. We also speculate on future developments.

   hep-latPoS(2006)·7 citations
10. 10*

    Spatial string tension revisited

    M. Laine🇩🇪 · Y. Schroder🇩🇪

    The spatial string tension, a classic non-perturbative probe for the convergence of the weak-coupling expansion at high temperatures, can be determined in full QCD as well as in a dimensionally reduced effective theory. Comparing both approaches, we find surprisingly good agreement almost down to the critical temperature of the deconfinement phase transition.

    hep-latPoS(2006)·25 citations
11. 11*

    Vortex-Line Percolation in the Three-Dimensional Complex Ginzburg-Landau Model

    Elmar Bittner🇩🇪 · Axel Krinner🇩🇪 · Wolfhard Janke🇩🇪

    We study the phase transition of the three-dimensional complex |psi|^4 theory by considering the geometrically defined vortex-loop network as well as the magnetic properties of the system in the vicinity of the critical point. Using high-precision Monte Carlo techniques we examine an alternative formulation of the geometrical excitations in relation to the global O(2)-symmetry breaking, and check if both of them exhibit the same critical behavior leading to the same critical exponents and therefore to a consistent description of the phase transition. Different percolation observables are taken into account and compared with each other. We find that different definitions of constructing the vortex-loop network lead to different results in the thermodynamic limit, and the percolation thresholds do not coincide with the thermodynamic phase transition point.

    hep-latPoS(2006)·0 citations
12. 12*

    $1^{-+}$ exotic meson at light quark masses

    J. N. Hedditch🇦🇺 · W. Kamleh🇦🇺 · B. G. Lasscock🇦🇺 · D. B. Leinweber🇦🇺 · A. G. Williams🇦🇺 · J. M. Zanotti🇩🇪

    The mass of the $1^{-+}$ exotic meson, created with hybrid interpolating fields, is explored at light quark masses approaching 25 MeV ($m_{\pi }/m_{\rho }\simeq 1/3$). Access to such light quark masses is facilitated by the use of the Fat-Link Irrelevant Clover (FLIC) fermion action. Additionally, we make use of large ($20^3\times 40$) lattices to obtain good control of statistical and finite volume errors. Our results indicate that the $1^{-+}$ exotic exhibits significant curvature close the chiral limit, indicating previous linear extrapolations, far from the chiral regime, have overestimated the mass of the $1^{-+}$. We find for the first time in lattice studies a $1^{-+}$ mass in agreement with the ${\pi }_1(1600)$ candidate. We also find a strangeness $\pm$1 $J^P=1^{-}$ state with a mass close to 2 GeV.

    hep-latPRD(2005)·67 citations
13. 13*

    Non-perturbative plaquette in 3d pure SU(3)

    A. Hietanen🇫🇮 · K. Kajantie🇫🇮 · M. Laine🇩🇪 · K. Rummukainen🇫🇮 · Y. Schroder🇩🇪

    We present a determination of the elementary plaquette and, after the subsequent ultraviolet subtractions, of the finite part of the gluon condensate, in lattice regularization in three-dimensional pure SU(3) gauge theory. Through a change of regularization scheme to MSbar and a matching back to full four-dimensional QCD, this result determines the first non-perturbative contribution in the weak-coupling expansion of hot QCD pressure.

    hep-latPoS(2006)·7 citations
14. 14*

    B meson decays at high velocity from mNRQCD

    A. Dougall🇬🇧 · Kerryann M. Foley🇺🇸 · C. T. H. Davies🇬🇧 · G. Peter Lepage🇺🇸

    The moving NRQCD (mNRQCD) formalism facilitates the simulation of heavy meson decays at large recoil. We present preliminary results for a number of quantities including the energy splittings and the $B$ meson decay constant that demonstrate that the formalism is accurate over a range of momenta.

    hep-latPoS(2006)·10 citations
15. 15*

    The Exotic Baryon Theta^+(1540) on the Lattice

    Dieter Hierl🇩🇪 · Christian Hagen🇩🇪 · Andreas Schaefer🇩🇪

    We report on a study of the pentaquark Theta^+(1540), using a variety of different interpolating fields. We use Chirally Improved fermions in combination with Jacobi smeared quark sources to improve the signal and get reliable results even for small quark masses. The results of our quenched calculations, which have been done on a 12^3x24 lattice with a lattice spacing of a=0.148 fm, do not provide any evidence for the existence of a Theta^+ with positive parity. We do observe, however, a signal compatible with nucleon-kaon scattering state. For the negative parity the results are inconclusive, due to the potential mixture with nucleon-kaon and N*-kaon scattering states.

    hep-latPoS(2006)·1 citation
16. 16*

    Heavy two- and three-quark free energies at finite $T$

    K. Hübner🇩🇪 · O. Kaczmarek🇩🇪 · O. Vogt🇩🇪

    We investigate the behaviour of heavy $QQ$- and $QQQ$-free energies in SU(3) pure gauge theory at finite temperature. After stating some general properties of the free energies, we discuss the $QQ$-antitriplet and -sextet channels as well as free energies in different $QQQ$-channels. We perform a detailed finite volume scaling analysis of $QQ$-free energies below and above $T_c$. Moreover, we also discuss the relation of the $QQ$-antitriplet to the $Q\bar{Q}$-singlet free energies. A comparison of the effective running coupling indicates that the $r$-dependence of the free energies differs by a factor of two in agreement with the different Casimir factors. We observe that the baryonic free energies can be decomposed into a sum of two particle interactions.

    hep-latPoS(2006)·5 citations
17. 17*

    UV-filtered overlap fermions

    Stephan Dürr🇨🇭 · Christian Hoelbling🇩🇪 · Urs Wenger🇩🇪

    We discuss the kernel spectrum, locality properties and the axial-vector renormalization constant of UV-filtered overlap fermions. We find that UV-filtered overlap fermions have a better conditioned kernel, better locality and an axial-vector renormalization constant closer to 1 than their unfiltered counterparts, even if the shift parameter $\rho$ is simply set to 1.

    hep-latPoS(2006)·4 citations
18. 18*

    Evaporation/Condensation of Ising Droplets

    Andreas Nussbaumer🇩🇪 · Elmar Bittner🇩🇪 · Wolfhard Janke🇩🇪

    Recently Biskup et al. [Europhys. Lett. 60 (2002) 21] studied the behaviour of d-dimensional finite-volume liquid-vapour systems at a fixed excess $\delta N$ of particles above the ambient gas density. They identify a dimensionless parameter $\Delta (\delta N)$ and a universal constant ${\Delta }_{\mathrm{c}}(d)$ and show that for $\Delta <{\Delta }_c$ a droplet of the dense phase occurs while for $\Delta >{\Delta }_c$ the excess is absorbed in the background. The fraction ${\lambda }_{\Delta }$ of excess particles forming the droplet is given explicitly. Furthermore, they state, that the same is true for solid-gas systems. To verify these results, we have simulated the spin-1/2 Ising model on a square lattice at constant magnetisation equivalent to a fixed particle excess in the lattice-gas picture. We measured the largest minority droplet, corresponding to the solid phase, at various system sizes ($L=40,...,640$). Using analytic values for the spontaneous magnetisation $m_0$, the susceptibility $\chi$ and interfacial free energy ${\tau }_{\mathrm{W}}$ for the infinite system, we were able to determine ${\lambda }_{\Delta }$ in very good agreement with the theoretical prediction.

    hep-latPoS(2006)·0 citations
19. 19*

    Searching for diquarks in hadrons

    C. Alexandrou🇨🇾 · Ph de Forcrand🇨🇭 · B. Lucini🇨🇭

    Since the early days of QCD, it has been argued that inside hadrons quarks organise into substructures. Among those, popular pictures of various phenomena (including exotica and colour superconductivity) give a prominent role to diquarks, i.e. to colour antitriplet combinations of two quarks. Using a gauge-invariant setup, which combines the diquark with a static quark, we study spatial correlations of the two light quarks inside the diquark. After illustrating the setup, we discuss our first results for both the scalar (``good'') and the spin one (``bad'') diquark channels. In a regime in which $m_{\pi }\simeq 830$ MeV, our data show unambiguously that a scalar diquark forms with a size of $\simeq$ 0.9 fm. For the vector diquark we are able to put a lower bound of 4.1(7) fm on its size. We also investigate the mass splitting between the good and the bad diquark; our findings are compatible with phenomenologically inspired predictions for this quantity.

    hep-lathep-phPoS(2006)·20 citations
20. 20*

    Center Vortex Model for SU(3) Yang-Mills Theory

    Markus Quandt (1)🇩🇪 · Hugo Reinhardt (1)🇩🇪 · Michael Engelhardt (2) ((1) Tubingen University, (2) New Mexico State University)🇺🇸

    The center vortex model for the infrared sector of SU(3) Yang-Mills theory is reviewed. After discussing the physical foundations underlying the model, some technical aspects of its realisation are discussed. The confining properties of the model are presented in some detail and compared to known results from full lattice Yang-Mills theory. Particular emphasis is put on the new phenomenon of vortex branching, which is instrumental in establishing first order behaviour of the SU(3) phase transition. Finally, the vortex free energy is verified to furnish an order parameter for the deconfinement phase transition. It is shown to exhibit a weak discontinuity at the critical temperature, in agreement with predictions from lattice gauge theory.

    hep-latPoS(2006)·1 citation
21. 21*

    Charmonium spectral functions in Nf=2 QCD

    R. Morrin🇮🇪 · A.P. O Cais🇮🇪 · M.B. Oktay🇮🇪 · M.J. Peardon🇮🇪 · J.I. Skullerud🇮🇪 · G. Aarts🇬🇧 · C.R. Allton🇬🇧

    We report on a study of charmonium at high temperature in 2-flavour QCD. This is the first such study with dynamical fermions. Using an improved anisotropic lattice action, spectral functions are extracted from correlators in the vector and pseudoscalar channels. No signs of medium-induced suppression of the ground states are seen for temperatures up to 1.5T_c, while at T~2T_c there are clear signs of modifications. The current systematic and statistical uncertainties in our data, in particular the relatively coarse lattice and small volume, do not allow us to draw a firm conclusion at this stage.

    hep-lathep-phPoS(2006)·40 citations
22. 22*

    RG decimation-based approach to confinement and computation on coarser lattices

    E.T. Tomboulis🇺🇸

    A systematic procedure is presented for connecting short to long scales in LGT. Approximate decimations are used which can provide both upper and lower bounds on the partition function. Its exact value is then obtained by interpolation between the bounds. By iterating the procedure representations of the partition function as well as other physical quantities can be obtained on progressively coarser lattices. For SU(2) IR flow into the confining strong coupling regime results for any initial $\beta$.

    hep-latPoS(2006)·4 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.