Fri·Oct 12, 2007Friday·October 12, 2007

1. 01*

   Deflated BiCGStab for linear equations in QCD problems

   Abdou Abdel-Rehim🇺🇸 · Ronald B. Morgan🇺🇸 · Walter Wilcox🇺🇸

   The large systems of complex linear equations that are generated in QCD problems often have multiple right-hand sides (for multiple sources) and multiple shifts (for multiple masses). Deflated GMRES methods have previously been developed for solving multiple right-hand sides. Eigenvectors are generated during solution of the first right-hand side and used to speed up convergence for the other right-hand sides. Here we discuss deflating non-restarted methods such as BiCGStab. For effective deflation, both left and right eigenvectors are needed. Fortunately, with the Wilson matrix, left eigenvectors can be derived from the right eigenvectors. We demonstrate for difficult problems with kappa near kappa_c that deflating eigenvalues can significantly improve BiCGStab. We also will look at improving solution of twisted mass problems with multiple shifts. Projecting over previous solutions is an easy way to reduce the work needed.

   hep-latPoS(2007)·4 citations
2. 02*

   Screening masses in the SU(3) pure gauge theory and universality

   Rossella Falcone🇮🇹 · Roberto Fiore🇮🇹 · Mario Gravina🇮🇹 · Alessandro Papa🇮🇹

   We determine from Polyakov loop correlators the screening masses in th e deconfined phase of the (3+1)d SU(3) pure gauge theory at finite temperature near transition, for two different channels of angular momentum and parity. Their ratio is compared with that of the massive excitations with the same quantum numbers in the 3d 3-state Potts model in the broken phase near the transition point at zero magnetic field. Moreover we study the inverse decay length of the correlation between the real parts and between the imaginary parts of the Polyakov loop and compare the results with expectations from perturbation theory and mean-field Polyakov loop models.

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

   Kaon semileptonic decay form factors from N_f = 2 non-perturbatively O(a)-improved Wilson fermions

   QCDSF Collaboration: D. Brommel🇩🇪 · R. Horsley🇬🇧 · S.M. Morozov🇷🇺 · Y. Nakamura🇩🇪 · D. Pleiter🇩🇪 · G. Schierholz🇩🇪 · H. Stuben🇩🇪 · J.M. Zanotti🇬🇧

   We present first results from the QCDSF collaboration for the kaon semileptonic decay form factors at zero momentum transfer, using two flavours of non-perturbatively O(a)-improved Wilson quarks. A lattice determination of these form factors is of particular interest to improve the accuracy on the CKM matrix element |V_us|. Calculations are performed on lattices with lattice spacing of about 0.08 fm with different values of light and strange quark masses, which allows us to extrapolate to chiral limit. Employing double ratio techniques, we are able to get small statistical errors.

   hep-latPoS(2007)·33 citations
4. 04*

   Nucleon electromagnetic form factors with Wilson fermions

   M. Gockeler🇩🇪 · Ph. Hagler🇩🇪 · R. Horsley🇬🇧 · Y. Nakamura🇩🇪 · M. Ohtani🇩🇪 · D. Pleiter🇩🇪 · P. E. L. Rakow🇬🇧 · A. Schafer🇩🇪 · G. Schierholz🇩🇪 · W. Schroers🇩🇪 · H. Stuben🇩🇪 · J. M. Zanotti🇬🇧

   The nucleon electromagnetic form factors continue to be of major interest for experimentalists and phenomenologists alike. They provide important insights into the structure of nuclear matter. For a range of interesting momenta they can be calculated on the lattice. The limiting factor continues to be the value of the pion mass. We present the latest results of the QCDSF collaboration using gauge configurations with two dynamical, non-perturbatively improved Wilson fermions at pion masses as low as 350 MeV.

   hep-latPoS(2007)·27 citations
5. 05*

   Nucleon and Nucleon to Delta Axial form factors from Lattice QCD

   C. Alexandrou (Univ. of Cyprus)🇨🇾 · G. Koutsou (Univ. of Cyprus)🇨🇾 · Th. Leontiou (Univ. of Cyprus)🇨🇾 · J. W. Negele (MIT)🇺🇸 · A. Tsapalis (IASA, Univ. of Athens)🇬🇷

   We present results on the nucleon axial vector form factors $G_A(q^2)$ and $G_p(q^2)$ in the quenched theory and using two degenerate flavors of dynamical Wilson fermions for momentum transfer squared from about 0.1 to about 2 GeV^2 and for pion masses in the range of 380 to 600 MeV. We also present results on the corresponding N to Delta axial vector transition form factors $C_5^A(q^2)$ and $C_6^A(q^2)$ using, in addition to Wilson fermions, domain wall valence quarks and dynamical staggered sea quarks provided by the MILC collaboration.

   hep-latPoS(2007)·7 citations
6. 06*

   Cluster simulation of two-dimensional relativistic fermions

   Ulli Wolff🇩🇪

   The (discrete) Gross-Neveu model is studied in a lattice realization with an N-component Majorana Wilson fermion field. It has an internal O(N) symmetry in addition to the euclidean lattice symmetries. The discrete chiral symmetry for vanishing mass is expected to emerge in the continuum limit only. The lattice theory is first recast in terms of two-valued bosonic link variables (dimers). In this representation, which coincides with the loop representation obtained earlier by Gattringer with the help of eight-vertex-models, the Boltzmann weight is essentially positive. While standard local updates are possible in this form we construct a further exact transformation where we generate dimer configurations as Peierls contours of an Ising model with a local action residing on plaquettes. For this model a Swendsen-Wang type cluster algorithm is constructed. At vanishing coupling it is numerically demonstrated to almost completely eliminate critical slowing down. Although further tests are required, an avenue to numerical studies of the Gross-Neveu model with unprecedented precision seems open.

   hep-latPoS(2007)·1 citation
7. 07*

   Heavy-strange meson decay constants in the continuum limit of quenched QCD

   Michele Della Morte (CERN)🇨🇭 · Stephan Durr (Bern U.)🇨🇭 · Damiano Guazzini (DESY)🇩🇪 · Jochen Heitger (Muenster U.)🇩🇪 · Andreas Juttner (Southampton U.)🇬🇧 · Rainer Sommer (DESY)🇩🇪

   We improve a previous quenched result for heavy-light pseudoscalar meson decay constants with the light quark taken to be the strange quark. A finer lattice resolution (a ~ 0.05 fm) in the continuum limit extrapolation of the data computed in the static approximation is included. We also give further details concerning the techniques used in order to keep the statistical and systematic errors at large lattice sizes L/a under control. Our final result, obtained by combining these data with determinations of the decay constant for pseudoscalar mesons around the D_s, follows nicely the qualitative expectation of the 1/m-expansion with a (relative) 1/m-term of about -0.5 GeV/m_PS. At the physical b-quark mass we obtain F_{B_s} = 193(7) MeV, where all errors apart from the quenched approximation are included.

   hep-lathep-phJHEP(2008)·25 citations
8. 08*

   Precision for B-meson matrix elements

   Damiano Guazzini🇩🇪 · Rainer Sommer🇩🇪 · Nazario Tantalo🇮🇹

   We demonstrate how HQET and the Step Scaling Method for B-physics, pioneered by the Tor Vergata group, can be combined to reach a further improved precision. The observables considered are the mass of the b-quark and the B_s-meson decay constant. The demonstration is carried out in quenched lattice QCD. We start from a small volume, where one can use a standard O(a)-improved relativistic action for the b-quark, and compute two step scaling functions which relate the observables to the large volume ones. In all steps we extrapolate to the continuum limit, separately in HQET and in QCD for masses below m_b. The physical point m_b is then reached by an interpolation of the continuum results in 1/m. The essential, expected and verified, feature is that the step scaling fuctions have a weak mass-dependence resulting in an easy interpolation to the physical point. With r_0=0.5fm and the experimental B_s and K masses as input, we find F_Bs=191(6)MeV and the renormalization group invariant mass M_b=6.88(10)GeV, translating into m_b(m_b)=4.42(6)GeV in the MSbar scheme. This approach seems very promising for full QCD.

   hep-latJHEP(2008)·29 citations
9. 09*

   Phenomenological applications of non-perturbative heavy quark effective theory

   Mauro Papinutto🇨🇭

   We briefly review the strategy to perform non-perturbative heavy quark effective theory computations and we specialize to the case of the b quark mass which has recently been computed including the 1/m term.

   hep-latJ.Phys.Conf.Ser.(2008)·0 citations
10. 10*

    Renormalization of Polyakov loops in fundamental and higher representations

    Olaf Kaczmarek🇩🇪 · Sourendu Gupta🇮🇳 · Kay Hubner🇺🇸

    We compare two renormalization procedures, one based on the short distance behavior of heavy quark-antiquark free energies and the other by using bare Polyakov loops at different temporal extent of the lattice and find that both prescriptions are equivalent, resulting in renormalization constants that depend on the bare coupling. Furthermore these renormalization constants show Casimir scaling for higher representations of the Polyakov loops. The analysis of Polyakov loops in different representations of the color SU(3) group indicates that a simple perturbative inspired relation in terms of the quadratic Casimir operator is realized to a good approximation at temperatures $T\text{gsim}{T}_c$ for renormalized as well as bare loops. In contrast to a vanishing Polyakov loop in representations with non-zero triality in the confined phase, the adjoint loops are small but non-zero even for temperatures below the critical one. The adjoint quark-antiquark pairs exhibit screening. This behavior can be related to the binding energy of gluelump states.

    hep-lathep-phPoS(2007)·4 citations
11. 11*

    High temperature expansion in supersymmetric matrix quantum mechanics

    Naoyuki Kawahara (KEK)🇯🇵 · Jun Nishimura (KEK, SOKENDAI)🇯🇵 · Shingo Takeuchi (SOKENDAI)🇯🇵

    We formulate the high temperature expansion in supersymmetric matrix quantum mechanics with 4, 8 and 16 supercharges. The models can be obtained by dimensionally reducing N=1 U(N) super Yang-Mills theory in D=4,6,10 to 1 dimension, respectively. While the non-zero frequency modes become weakly coupled at high temperature, the zero modes remain strongly coupled. We find, however, that the integration over the zero modes that remains after integrating out all the non-zero modes perturbatively, reduces to the evaluation of connected Green's functions in the bosonic IKKT model. We perform Monte Carlo simulation to compute these Green's functions, which are then used to obtain the coefficients of the high temperature expansion for various quantities up to the next-leading order. Our results nicely reproduce the asymptotic behaviors of the recent simulation results at finite temperature. In particular, the fermionic matrices, which decouple at the leading order, give rise to substantial effects at the next-leading order, reflecting finite temperature behaviors qualitatively different from the corresponding models without fermions.

    ↳ hep-thhep-latJHEP(2007)·64 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.