Mon·Oct 15, 2007Monday·October 15, 2007

1. 01*

   Glueballs in Flatland

   Robert W. Johnson Jr🇬🇧

   The pure gauge theory in 2+1 dimensions is explored, through both a phenomenological model and a lattice calculation. The Isgur-Paton model is extended to include a curvature term and various mixing mechanisms. The method of inferential statistics is used to extract the parameters of best fit and to compare the likelihoods of the various models when compared to existing lattice data. The conventional assignment of spin 0 to the pseudoscalar state is called into question by the proximity of a spin 4 state in the model, which motivates calculating the mass of the spin 4 state on the lattice. Novel lattice operators are constructed from a matrix of effective Greens functions which attempt to overcome the lattice rotational ambiguities. Correlation functions are presented for the channels with even J, and effective masses extracted. The resulting masses compare well with the extended Isgur-Paton model.

   hep-lat0 citations
2. 02*

   Magnetic Moment of Vector Mesons in the Background Field Method

   Frank X. Lee🇺🇸 · Scott Moerschbacher🇺🇸 · Walter Wilcox🇺🇸

   We report some results for the magnetic moments of vector mesons extracted from mass shifts in the presence of static external magnetic fields. The calculations are done on $24^4$ quenched lattices using standard Wilson actions, with $\beta$=6.0 and pion mass down to 500 MeV. The results are compared to those from the form factor method.

   hep-latPoS(2007)·0 citations
3. 03*

   Aspects of QCD Vacuum Structure

   Peter J. Moran🇦🇺 · Derek B. Leinweber🇦🇺

   The impact of dynamical fermions on the vacuum structure of QCD is explored. Of particular interest is the topological charge correlator, $<q(x)q(0)>$, where negative values at small $x$ reveal a sign-alternating layered structure to the topological-charge density of the QCD vacuum. We consider large $28^3\times 96$ lattices from the MILC collaboration, and develop a new gluonic definition of the topological charge density, founded on a new over-improved stout-link smearing algorithm. The algorithm reproduces established results from the overlap formalism and is designed to preserve instantons. We examine the extent to which instanton-like objects are found on the lattice. Finally, we investigate the effects of dynamical sea-quark degrees of freedom on topology and find that the magnitudes of the negative dip in the $<q(x)q(0)>$ correlator and the positive $<q(0{)}^2>$ contact term are both increased with the introduction of dynamical fermion degrees of freedom. This is in accord with expectations based on charge renormalization and the vanishing of the topological susceptibility in the chiral limit.

   hep-latPoS(2007)·7 citations
4. 04*

   Pion form factor from all-to-all propagators of overlap quarks

   JLQCD collaboration: T.Kaneko🇯🇵 · H.Fukaya🇯🇵 · S.Hashimoto🇯🇵 · H.Matsufuru🇯🇵 · J.Noaki🇯🇵 · T.Onogi🇯🇵 · N.Yamada🇯🇵

   We report on our calculation of the pion electromagnetic form factor with two-flavors of dynamical overlap quarks. Gauge configurations are generated using the Iwasaki gauge action on a 16^3 \times 32 lattice at the lattice spacing of 0.12fm with sea quark masses down to m_s/6, where m_s is the physical strange quark mass. We describe our setup to measure the form factor through all-to-all quark propagators and present preliminary results.

   hep-latPoS(2007)·23 citations
5. 05*

   Modified Lattice Landau Gauge

   Lorenz von Smekal🇦🇺 · Dhagash Mehta🇦🇺 · Andre Sternbeck🇦🇺 · Anthony G. Williams🇦🇺

   We propose a modified lattice Landau gauge based on stereographically projecting the link variables on the circle S^1 -> R for compact U(1) or the 3-sphere S^3 -> R^3 for SU(2) before imposing the Landau gauge condition. This can reduce the number of Gribov copies exponentially and solves the Gribov problem in compact U(1) where it is a lattice artifact. Applied to the maximal Abelian subgroup this might be just enough to avoid the perfect cancellation amongst the Gribov copies in a lattice BRST formulation for SU(N), and thus to avoid the Neuberger 0/0 problem. The continuum limit of the Landau gauge remains unchanged.

   hep-latPoS(2007)·73 citations
6. 06*

   Pion and $\rho$-meson form factors using four-point functions in N${}_F$=2 QCD

   Constantia Alexandrou🇨🇾 · Giannis Koutsou🇨🇾

   Hadron wave functions and form factors can be extracted using four-point correlators. Stochastic techniques are used to estimate the all to all propagators, which are required for the exact calculation of four-point functions. We apply the so called one-end trick to evaluate meson four-point functions. We demonstrate the effectiveness of the technique in the case of the pion and the $\rho$-meson where we extract their charge distribution, as well as the form factors.

   hep-latPoS(2007)·6 citations
7. 07*

   QCD on the Cell Broadband Engine

   F. Belletti · G. Bilardi · M. Drochner🇩🇪 · N. Eicker🇩🇪 · Z. Fodor🇩🇪 · D. Hierl🇩🇪 · H. Kaldass · T. Lippert🇩🇪 · T. Maurer🇩🇪 · N. Meyer🇩🇪 · A. Nobile🇮🇹 · D. Pleiter🇩🇪 and 7 other authors

   We evaluate IBM's Enhanced Cell Broadband Engine (BE) as a possible building block of a new generation of lattice QCD machines. The Enhanced Cell BE will provide full support of double-precision floating-point arithmetics, including IEEE-compliant rounding. We have developed a performance model and applied it to relevant lattice QCD kernels. The performance estimates are supported by micro- and application-benchmarks that have been obtained on currently available Cell BE-based computers, such as IBM QS20 blades and PlayStation 3. The results are encouraging and show that this processor is an interesting option for lattice QCD applications. For a massively parallel machine on the basis of the Cell BE, an application-optimized network needs to be developed.

   hep-latPoS(2007)·14 citations
8. 08*

   Determining QCD Low-Energy Couplings from lattice simulations

   Silvia Necco🇪🇸

   Different strategies for the computation of QCD low-energy couplings by matching lattice QCD with the chiral effective theory are reviewed. After recalling the main features of the chiral effective theory in the epsilon- and p- regimes, the current status of the determination of leading order (Sigma, F) and next-to-leading order (l_i, L_i) low-energy constants is summarised, focusing in particular on recent results obtained with N_f=2 and N_f=2+1 simulations.

   hep-lathep-phPoS(2007)·19 citations
9. 09*

   Lattice Approach to Light Scalars

   Craig McNeile🇬🇧

   I report on lattice QCD calculations that study the properties of the a0 and f0 mesons.

   hep-lateConf(2007)·9 citations
10. 10*

    Moments of nucleon distribution amplitudes from irreducible three-quark operators

    M.Göckeler🇩🇪 · R.Horsley🇬🇧 · T.Kaltenbrunner🇩🇪 · Y.Nakamura🇩🇪 · D.Pleiter🇩🇪 · P.E.L.Rakow🇬🇧 · A.Schäfer🇩🇪 · G.Schierholz🇩🇪 · H.Stüben🇩🇪 · N.Warkentin🇩🇪 · J.M.Zanotti🇬🇧

    Semi-exclusive and exclusive processes are becoming more and more important in high energy physics since they are excellently suited to study the internal hadronic structure. To analyze such processes the knowledge of the hadron distribution amplitudes, which are universal for different reactions, is essential. Only rather indirect information on these nonperturbative functions can be obtained from measurements. In this work we report on a lattice QCD computation of moments of nucleon distribution amplitudes using suitable three-quark operators. However, these operators have to be renormalized and the mixing is even more complicated than in the continuum. Using the symmetry group of the hypercubic lattice we therefore derive and implement irreducibly transforming three-quark operators, which allow us to control the mixing pattern and will finally lead to quantitative predictions in the MSbar scheme. We present preliminary results for leading-twist and next-to-leading twist nucleon distribution amplitudes based on the QCDSF/UKQCD simulations with 2 flavors of dynamical clover fermions.

    hep-latPoS(2007)·17 citations
11. 11*

    O(a^2) cutoff effects in Wilson fermion simulations

    Roberto Frezzotti🇮🇹 · Giancarlo Rossi (Univ. and INFN of Rome Tor Vergata - Italy)🇮🇹

    We show that the size of the O(a^2) flavour violating cutoff artifacts that have been found to affect the value of the neutral pion mass in simulations with maximally twisted Wilson fermions is controlled by a continuum QCD quantity that is fairly large and is determined by the dynamical mechanism of spontaneous chiral symmetry breaking. One can argue that the neutral pion mass is the only physical quantity blurred by such cutoff effects. O(a^2) corrections of this kind are also present in standard Wilson fermion simulations, but they can either affect the determination of the pion mass or be shifted from the latter to other observables, depending on the way the critical mass is evaluated.

    hep-latPoS(2007)·25 citations
12. 12*

    Scaling and low energy constants in lattice QCD with N_f=2 maximally twisted Wilson quarks

    ETM Collaboration: P. Dimopoulos🇮🇹 · R. Frezzotti🇮🇹 · G. Herdoiza🇮🇹 · C. Urbach🇬🇧 · U. Wenger🇨🇭

    We report on the scaling of basic hadronic observables in lattice QCD with N_f=2 maximally twisted Wilson dynamical quarks. We give preliminary results for some of the Gasser-Leutwyler low energy constants, the chiral condensate and the average mass of u and d quarks.

    hep-latPoS(2007)·28 citations
13. 13*

    Using $K^0{\pi }^{-}\to {\pi }^{-}$ transitions to compute $K\to (\pi \pi {)}_{I=0}$ decay amplitudes at NLO in the chiral expansion

    Changhoan Kim🇬🇧 · Christopher Sachrajda🇬🇧

    It is proposed to compute matrix elements for the (unphysical) $K^0{\pi }^{-}\to {\pi }^{-}$ transition to determine the next-to-leading order low energy constants of the weak chiral Lagrangian. This allows us to evaluate $K\to (\pi \pi {)}_{I=0}$ decay amplitudes at this level of precision. This approach has several significant advantages over the use of $K\to \pi \pi$ transitions, most notably the elimination of s-channel disconnected diagrams and the use of fewer inversions.

    hep-latPoS(2007)·2 citations
14. 14*

    The equation of state with nonzero chemical potential for 2+1 flavors

    C. Bernard🇺🇸 · T. Burch🇩🇪 · C. DeTar🇺🇸 · L. Levkova🇺🇸 · Steven Gottlieb🇺🇸 · U.M. Heller🇺🇸 · J.E. Hetrick🇺🇸 · R. Sugar🇺🇸 · D. Toussaint🇺🇸

    We present results for the QCD equation of state with nonzero chemical potential using the Taylor expansion method with terms up to sixth order in the expansion. Our calculations are performed on asqtad 2+1 quark flavor lattices at $N_t=4$.

    hep-latPoS(2007)·1 citation

* 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.