Tue·Oct 2, 2007Tuesday·October 2, 2007

1. 01*

   Parameter Tuning of Three-Flavor Dynamical Anisotropic Clover Action

   Huey-Wen Lin🇺🇸 · Robert G. Edwards🇺🇸 · Bálint Joó🇺🇸

   In this work, we perform parameter tuning with dynamical anisotropic clover lattices using the Schrödinger functional and stout-smearing in the fermion field. We find that ${\xi }_R/{\xi }_0$ is relatively close to 1 in our parameter search, which allows us to fix ${\xi }_0$ in our runs. We proposed to determine the gauge and fermion anisotropy in a Schrödinger-background small box using Wilson loop ratios and PCAC masses. We demonstrate that these ideas are equivalent to but more efficient than the conventional meson dispersion approach. The spatial and temporal clover coefficients are fixed to the tree-level tadpole-improved clover values, and we demonstrate that they satisfy the nonperturbative condition determined by Schrödinger functional method.

   hep-latPoS(2007)·5 citations
2. 02*

   Using evolutionary algorithms to extract field theory mass spectra

   Georg M. von Hippel🇨🇦 · Randy Lewis🇨🇦 · Robert G. Petry🇨🇦

   The spectrum of masses from a lattice QCD simulation may be found by fitting exponential functions to correlators of operators possessing the quantum numbers of the particles of interest. The ability of evolutionary algorithms to find globally optimized solutions containing a variable number of states across multiple data sets is exploited to provide a promising solution to the problem of finding these fits.

   hep-latPoS(2007)·8 citations
3. 03*

   Improvement of the pion spectrum with HYP-smeared staggered fermions

   Taegil Bae🇰🇷 · David Adams🇰🇷 · Chulwoo Jung🇺🇸 · Hyung-Jin Kim · Jongjeong Kim · Kwangwoo Kim · Weonjong Lee🇰🇷 · Stephen R. Sharpe🇺🇸

   We extend our previous study of taste-symmetry breaking using HYP-smeared staggered fermions in two ways. First, we improve the statistics of a comparison of unimproved and HYP-smeared staggered fermions on quenched lattices with $a\approx 0.1$fm. This allows us to obtain a signal for all pion tastes, rather than just a subset, and thus to make a complete comparison. In addition, it allows us to differentiate between wall and local sources. Second, we compare HYP-smeared valence quarks to asqtad valence quarks on 2+1 flavor unquenched MILC lattices. We find that taste breaking is substantially reduced by HYP-smearing, bringing the size of this discretization effect (which is the dominant such effect with staggered fermions) down to the size expected generically for any fermion type.

   hep-latPoS(2007)·2 citations
4. 04*

   The Glue Content of the Pion

   Harvey B. Meyer🇺🇸 · John W. Negele🇺🇸

   We perform a quenched computation of the glue momentum fraction in the pion. Different discretizations of the gluonic energy-momentum tensor are studied on the lattice for that purpose. We discuss some implications based on the momentum sum rule. Finally we point out promising applications of the techniques developed here.

   hep-latPoS(2007)·4 citations
5. 05*

   HMC algorithm for two-flavour lattice QCD: Schwarz-preconditioning with a one-dimensional domain decomposition

   Martin Hasenbusch🇮🇹

   We study a variant of the Schwarz-preconditioned HMC algorithm. In contrast to the original proposal of Lüscher, we apply the domain decomposition in one lattice direction only. This is sufficient to reduce the condition number of the fermion matrix restricted to the domains compared with the full fermion matrix. For the same linear extension of the domain, less links reside on the boundaries of the domains. Therefore it becomes e.g. practical to iterate the decomposition. We perform numerical tests for two degenerate flavours of Wilson fermions. The standard Wilson gauge action at $\beta =5.6$ is used. The performance of our implementation is compared with other recent studies using various types of preconditioning.

   hep-latPoS(2007)·4 citations
6. 06*

   The vector and axial vector current in Wilson ChPT

   Sinya Aoki🇯🇵 · Oliver Bar🇩🇪

   We construct the vector and axial vector currents in Wilson Chiral Perturbation Theory (WChPT), the low-energy effective theory for lattice QCD with Wilson fermions. Our construction is slightly different compared to ChPT in continuum QCD, where the currents are essentially the (partially) conserved currents associated with the chiral symmetries. In WChPT, due to explicit chiral symmetry breaking at non-zero lattice spacing, there appear O(a) terms in the expressions for the currents which do not stem from the effective action. In addition, the finite renormalization of the currents needs to be taken into account in order to properly match the currents of the effective theory. As an illustration we compute f_pi to one loop with the renormalized axial vector current for a particular renormalization condition. It turns out that for this particular condition some of the O(a) corrections are taken care of by the renormalization.

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

   Pseudo-scalar meson form factors with maximally twisted Wilson fermions at Nf = 2

   ETM Collaboration: S. Simula🇮🇹

   We present preliminary results for various electroweak form factors of pseudo-scalar mesons using the tree-level improved Symanzik gauge action and the maximally twisted mass fermionic action with Nf = 2 dynamical flavors. Our results, obtained for both light and heavy quark masses at a single lattice spacing (a ~ 0.09 fm) and at a single lattice volume (V * T = 24**3 * 48), exhibit a quite remarkable statistical precision thanks to the use of all-to-all quark propagators computed with a stochastic method. Moreover very low values of the four-momentum transfer are achieved by making use of twisted boundary conditions on the valence quark fields. The mass dependence of the pion charge radius is analyzed using Chiral Perturbation Theory, obtaining clear evidence of relevant two-loop contributions. The universal Isgur-Wise function is computed from heavy-to-heavy electromagnetic transitions and its slope in the case of $u(d)$ spectator quarks is found to be rho(IW)**2 = 0.77 +/- 0.28, where the error is statistical only.

   hep-lathep-phPoS(2007)·30 citations
8. 08*

   A survey of large N continuum phase transitions

   R. Narayanan🇺🇸 · H. Neuberger🇺🇸

   The main focus of this talk is the physics of large N QCD on a continuum torus. A cascade of phase transitions associated with the breaking of U(1) symmetries will be discussed. The continuum Wilson loop as a function of its area will be discussed along with its universality properties and the associated double scaling limit. Some recent progress in twisted Eguchi-Kawai is presented. Gauge field topology and $\theta$ vacuua are also discussed in the context of large N gauge theories. Phase transitions in 2D large N principal chiral models are compared with similar transitions in large $N$ gauge theories. Finally, connections to some topics in string theory and gravity are briefly described.

   hep-lathep-thPoS(2007)·18 citations
9. 09*

   High density effective theory on the lattice

   A. Dougall🇬🇧

   Long-range interactions in finite density QCD necessitate a non-perturbative approach in order to reliably map out the key features and spectrum of the QCD phase diagram. However, the complex nature of the fermion determinant in this sector prohibits the use of established Monte Carlo techniques that utilize importance sampling. Whilst significant progress has been made in the low density, high temperature region, this remains a considerable challenge at mid to high density. At large chemical potential, QCD can be approximated using high density effective theory which is free from the sign problem at leading order. We investigate the implementation of this theory on the lattice in conjunction with existing re-weighting techniques.

   hep-latPoS(2007)·2 citations
10. 10*

    A test of first order scaling in Nf=2 QCD

    G. Cossu🇮🇹 · M. D'Elia🇮🇹 · A. Di Giacomo🇮🇹 · C. Pica🇺🇸

    We complete our analysis of Nf=2 QCD based on the lattice staggered fermion formulation. Using a series of Monte Carlo simulations at fixed (amq*Ls^yh) one is able to test the universality class with given critical exponent yh. This strategy has been used to test the O(4) universality class and it has been presented at the previous Lattice conferences. No agreement was found with simulations in the mass range amq=[0.01335,0.15] using lattices with Ls=16 up to 32 and Lt=4. With the same strategy, we now investigate the possibility of a first order transition using a new set of Monte Carlo data corresponding to yh=3 in the same mass and volume range as the one used for O(4). A substantial agreement is observed both in the specific heat scaling and in the scaling of the chiral condensate, while the chiral susceptibilities still presents visible deviation from scaling in the mass range explored.

    hep-latPoS(2007)·6 citations
11. 11*

    Study of constant mode in charmonium correlators at finite temperature

    Takashi Umeda🇯🇵

    Recent studies on the spectral function of charmonium in lattice QCD suggest survival of $J/\psi$ state in the deconfinement phase till relatively high temperature. Based on the studies, different scenarios of $J/\psi$ suppression are discussed to understand experimental results in the Heavy Ion Collision experiments. The scenarios require the information on the dissociation temperatures of ${\chi }_c$ and ${\psi }^{\prime }$ as well as that of $J/\psi$. In order to investigate these states in finite temperature lattice QCD, we have to consider an effect of a characteristic constant mode in the correlators. As a result of the study on the constant mode, we find that most drastic change in charmonium correlators for ${\chi }_c$ states just above the deconfinement transition are caused by the constant mode. It may indicate the survival of ${\chi }_c$ states after the deconfinement transition until, at least, $1.4T_c$.

    hep-latPoS(2007)·5 citations
12. 12*

    Marking up lattice QCD configurations and ensembles

    P.Coddington🇦🇺 · B.Joo🇺🇸 · C.M.Maynard🇬🇧 · D.Pleiter🇩🇪 · T.Yoshie (ILDG Metadata Working Group)🇯🇵

    QCDml is an XML-based markup language designed for sharing QCD configurations and ensembles world-wide via the International Lattice Data Grid (ILDG). Based on the latest release, we present key ingredients of the QCDml in order to provide some starting points for colleagues in this community to markup valuable configurations and submit them to the ILDG.

    hep-latPoS(2007)·9 citations
13. 13*

    Charmonium spectrum including higher spin and exotic states

    Christian Ehmann🇩🇪 · Gunnar Bali🇩🇪

    We study the charmonium spectrum including higher spin and exotic states. We use the Sheikholeslami-Wilson (clover) action for $N_f=2$ sea quarks as well as for the charm valence quark. In order to access excited states we apply a variational method with a basis of highly optimized operators.

    hep-latPoS(2007)·16 citations
14. 14*

    Baryon currents in the C-broken phase of QCD

    Biagio Lucini🇬🇧 · Agostino Patella🇮🇹 · Claudio Pica🇺🇸

    In a space with some sufficiently small compact dimension (with non-trivial cycles) and with periodic boundary conditions for the fermions, the charge conjugation (C), spatial parity (P), time reversal (T) and CPT symmetries are spontaneously broken in QCD. We have investigated what are the physical consequences of the breaking of these discrete symmetries, that is what local observables can be used to detect it. We show that the breaking induces the generation of baryon currents, propagating along the compact dimensions.

    hep-latPoS(2007)·1 citation
15. 15*

    Thin and dressed Polyakov loops from spectral sums of lattice differential operators

    Erek Bilgici🇦🇹 · Christian Hagen🇩🇪 · Falk Bruckmann🇩🇪 · Christof Gattringer🇦🇹

    We represent thin and dressed Polyakov loops as spectral sums of eigenvalues of differential operators on the lattice. For that purpose we calculate complete sets of eigenvalues of the staggered Dirac and the covariant Laplace operator for several temporal boundary conditions. The spectra from different boundary conditions can be combined such that they represent single (thin) Polyakov loops, or a collection of loops (dressed Polyakov loops). We analyze the role of the eigenvalues in the spectral sums below and above the critical temperature.

    hep-latPoS(2007)·13 citations
16. 16*

    A Dual Algorithm for Non-abelian Yang-Mills coupled to Dynamical Fermions

    J. Wade Cherrington🇨🇦

    We extend the dual algorithm recently described for pure, non-abelian Yang-Mills on the lattice to the case of lattice fermions coupled to Yang-Mills, by constructing an ergodic Metropolis algorithm for dynamic fermions that is local, exact, and built from gauge-invariant boson-fermion coupled configurations. For concreteness, we present in detail the case of three dimensions, for the group SU(2) and staggered fermions, however the algorithm readily generalizes with regard to group and dimension. The treatment of the fermion determinant makes use of a polymer expansion; as with previous proposals making use of the polymer expansion in higher than two dimensions, the critical question for practical applications is whether the presence of negative amplitudes can be managed in the continuum limit.

    hep-latNPB(2008)·14 citations
17. 17*

    Light quark masses and pseudoscalar decay constants from Nf=2 twisted mass QCD

    Vittorio Lubicz🇮🇹 · Silvano Simula🇮🇹 · Cecilia Tarantino🇮🇹

    We present the results of the lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants, recently performed with Nf=2 dynamical fermions by the ETM Collaboration. The simulation is carried out at a single value of the lattice spacing with the twisted mass fermionic action at maximal twist, which guarantees automatic O(a)-improvement of the physical quantities. Quark masses are renormalized by implementing the non perturbative RI-MOM renormalization procedure. Our results for the light quark masses are m_{ud}^{MSbar}(2 Gev)=3.85 +- 0.12 +- 0.40 MeV, m_s^{MSbar}(2 Gev)=105 +- 3 +- 9 MeV and m_s/m_{ud}=27.3 +- 0.3 +- 1.2. We also obtain f_K=161.7 +- 1.2 +- 3.1 MeV and the ratio f_K/f_pi=1.227 +- 0.009 +- 0.024. From this ratio, by using the experimental determination of Gamma(K -> mu {bar nu}_mu (gamma))/Gamma(pi -> mu {bar nu}_mu (gamma)) and the average value of |V_{ud}| from nuclear beta decays, we obtain |V_{us}|=0.2192(5)(45), in agreement with the determination from K_{l3} decays and the unitarity constraint.

    hep-lathep-phPoS(2007)·5 citations
18. 18*

    High-temperature expansions through order 24 for the two-dimensional classical XY model on the square lattice

    P. Butera🇮🇹 · M. Pernici🇮🇹

    The high-temperature expansion of the spin-spin correlation function of the two-dimensional classical XY (planar rotator) model on the square lattice is extended by three terms, from order 21 through order 24, and analyzed to improve the estimates of the critical parameters.

    hep-latcond-mat.stat-mechPRB(2007)·8 citations
19. 19*

    An iterative method to compute the overlap Dirac operator at nonzero chemical potential

    Jacques Bloch🇩🇪 · Andreas Frommer🇩🇪 · Bruno Lang🇩🇪 · Tilo Wettig🇩🇪

    The overlap Dirac operator at nonzero quark chemical potential involves the computation of the sign function of a non-Hermitian matrix. In this talk we present an iterative method, first proposed by us in Ref. [1], which allows for an efficient computation of the operator, even on large lattices. The starting point is a Krylov subspace approximation, based on the Arnoldi algorithm, for the evaluation of a generic matrix function. The efficiency of this method is spoiled when the matrix has eigenvalues close to a function discontinuity. To cure this, a small number of critical eigenvectors are added to the Krylov subspace, and two different deflation schemes are proposed in this augmented subspace. The ensuing method is then applied to the sign function of the overlap Dirac operator, for two different lattice sizes. The sign function has a discontinuity along the imaginary axis, and the numerical results show how deflation dramatically improves the efficiency of the method.

    hep-latPoS(2007)·3 citations
20. 20*

    SU(2) meets SU(3) in lattice-Landau-gauge gluon and ghost propagators

    A. Cucchieri🇧🇷 · T. Mendes🇧🇷 · O. Oliveira🇵🇹 · P. J. Silva🇵🇹

    A comparative study of the lattice Landau gauge gluon and ghost propagators for SU(2) and SU(3) pure Yang-Mills theories is carried out. The data were specially produced with equivalent lattice parameters to allow for a careful comparison of the two cases. We find very good agreement between the two theories. Our results seem to confirm the predicton of Schwinger-Dyson equations that the infrared exponents are independent of the gauge group SU(N).

    hep-latPoS(2007)·7 citations
21. 21*

    Staggered Diquarks for the Singly Heavy Baryons

    Steven Gottlieb🇺🇸 · Heechang Na🇺🇸 · Kazuhiro Nagata🇺🇸

    In the staggered fermion formulation of lattice QCD, we construct diquark operators to be embedded in singly heavy baryons. The group theoretical connections between the continuum and lattice staggered diquark representations are established.

    hep-latPoS(2007)·2 citations
22. 22*

    Hamiltonian approach to Coulomb gauge Yang-Mills Theory

    H. Reinhardt🇩🇪 · W. Schleifenbaum🇩🇪 · D. Epple🇩🇪 · C. Feuchter🇩🇪

    The vacuum wave functional of Coulomb gauge Yang-Mills theory is determined within the variational principle and used to calculate various Green functions and observables. The results show that heavy quarks are confined by a linearly rising potential and gluons cannot propagate over large distances. The 't Hooft loop shows a perimeter law and thus also indicates confinement.

    ↳ hep-thhep-lathep-phPoS(2007)·2 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.