Mon·Sep 20, 2004Monday·September 20, 2004

1. 01*

   Static $\bar{Q}$-$Q$ Potential from $N_f=2$ Dynamical Domain-Wall QCD

   Koichi Hashimoto🇯🇵 · Taku Izubuchi (for the RBC Collaboration)🇺🇸

   We calculate the static quark and anti-quark potential both in quenched and two-flavor dynamical quark lattice QCD using DBW2 gauge and domain-wall quark actions. Lattice spacings from Sommer scale are determined. We find (i) mixing of excited states is different in between quenched and dynamical, (ii) lattice spacing $a_{r_0}\sim a_{m_{\rho }}$ in dynamical and (iii) coefficient of Coulomb term being ${\alpha }_{N_f=0}<{\alpha }_{N_f=2}$ at $a^{-1}\sim$ 2 GeV.

   hep-latNucl.Phys.B Proc.Suppl.(2005)·8 citations
2. 02*

   Lattice Study of the O(3) Supersymmetric Sigma Model

   Sofiane Ghadab🇺🇸

   We present preliminary numerical results from a lattice study of the two-dimensional O(3) non-linear sigma model. In the continuum this model possesses N=2 supersymmetry. The lattice formulation we use retains an exact (twisted) supersymmetry except for a soft breaking associated with a Wilson mass term needed to remove the doubles. Our numerical results show that the partition function is independent of coupling as predicted by supersymmetry.

   hep-latNucl.Phys.B Proc.Suppl.(2005)·4 citations
3. 03*

   Effects of low-lying fermion modes in the epsilon regime

   Kenji Ogawa (1)🇯🇵 · Shoji Hashimoto (2) ((1)Sokendai, (2) KEK)🇯🇵

   We investigate the effects of low-lying fermion modes on the QCD partition function in the epsilon-regime. With the overlap Dirac operator we calculate several tens of low-lying fermion eigenvalues on the quenched lattice. By partially incorporating the fermion determinant through the truncated determinant approximation, we calculate the partition function and other related quantities for Nf = 1 and compare them with the theoretical predictions obtained by Leutwyler and Smilga.

   hep-latNucl.Phys.B Proc.Suppl.(2005)·2 citations
4. 04*

   Penguin diagrams for improved staggered fermions

   Weonjong Lee🇰🇷

   We calculate, at the one loop level, penguin diagrams for improved staggered fermion operators constructed using various fat links. The main result is that diagonal mixing coefficients with penguin operators are identical between the unimproved operators and the improved operators using such fat links as Fat7, Fat7+Lepage, $\overline{Fat7}$, HYP (I) and HYP (II). In addition, it turns out that the off-diagonal mixing vanishes for those constructed using fat links of Fat7, $\overline{Fat7}$ and HYP (II). This is a consequence of the the fact that the improvement by various fat links changes only the mixing with higher dimension operators and off-diagonal operators. The results of this paper, combined with those for current-current diagrams, provide the complete matching at the one loop level with all corrections of $\mathcal{O}(g^2)$ included.

   hep-latPRD(2005)·0 citations
5. 05*

   Detailed analysis of the gluonic excitation in the three-quark system in lattice QCD

   T.T.Takahashi🇯🇵 · H.Suganuma🇯🇵

   We study the excited-state potential and the gluonic excitation in the static three-quark (3Q) system using SU(3) lattice QCD with $16^3\times 32$ at $\beta$=5.8 and 6.0 at the quenched level. For about 100 different patterns of spatially-fixed 3Q systems, we accurately extract the excited-state potential $V_{3Q}^{e.s.}$ together with the ground-state potential $V_{3Q}^{g.s.}$ by diagonalizing the QCD Hamiltonian in the presence of three quarks. The gluonic excitation energy $\Delta E_{3Q}\equiv V_{3Q}^{e.s.}-V_{3Q}^{g.s.}$ is found to be about 1 GeV at the typical hadronic scale. This large gluonic-excitation energy is conjectured to give a physical reason of the success of the quark model for low-lying hadrons even without explicit gluonic modes. We investigate the functional form of $\Delta E_{3Q}$ in terms of the 3Q location. The lattice data of $\Delta E_{3Q}$ are relatively well reproduced by the ``inverse Mercedes Ansatz'' with the ``modified Y-type flux-tube length'', which indicates that the gluonic-excitation mode is realized as a complicated bulk excitation of the whole 3Q system.

   hep-latPRD(2004)·51 citations
6. 06*

   Schwarz-preconditioned HMC algorithm for two-flavour lattice QCD

   Martin Lüscher🇨🇭

   The combination of a non-overlapping Schwarz preconditioner and the Hybrid Monte Carlo (HMC) algorithm is shown to yield an efficient simulation algorithm for two-flavour lattice QCD with Wilson quarks. Extensive tests are performed, on lattices of size up to 32x24x24x24, with lattice spacings a~0.08 fm and at bare current-quark masses as low as 21 MeV.

   hep-latComput.Phys.Commun.(2005)·291 citations
7. 07*

   Comparing iterative methods for overlap and twisted mass fermions

   T. Chiarappa🇩🇪 · K. Jansen🇩🇪 · K.-I. Nagai🇩🇪 · M. Papinutto🇩🇪 · L. Scorzato🇩🇪 · A. Shindler🇩🇪 · C. Urbach🇩🇪 · U. Wenger🇩🇪 · I. Wetzorke🇩🇪

   We present a systematic comparison of various iterative methods to obtain the fermion propagator with both overlap and twisted mass fermions at fixed pion mass in the quenched approximation. Taking the best available algorithm in each case we find that calculations with the overlap operator are by a factor of 20-40 more expensive than with the twisted mass operator at the parameter values considered here. For the overlap operator we also compare the efficiency of various methods for calculating the topological index.

   hep-latNucl.Phys.B Proc.Suppl.(2005)·13 citations
8. 08*

   A comparative study of overlap and staggered fermions in QCD

   S. Dürr🇩🇪 · Ch. Hoelbling🇫🇷 · U. Wenger🇩🇪

   We perform a comparative study of the infrared properties of overlap and staggered fermions in QCD. We observe that the infrared spectrum of the APE/HYP improved staggered Dirac operator develops a four-fold near-degeneracy and is in quantitative agreement with the infrared spectrum of the overlap operator. The near-degeneracy allows us to identify the zero modes of the staggered operator and we find that the number of zero modes is in line with the topological index of the overlap operator.

   hep-latNucl.Phys.B Proc.Suppl.(2005)·7 citations
9. 09*

   Comparison between overlap and twisted mass fermions towards the chiral limit

   W. Bietenholz🇩🇪 · S. Capitani🇦🇹 · T. Chiarappa🇩🇪 · M. Hasenbusch🇮🇹 · K. Jansen🇩🇪 · K.-I. Nagai🇩🇪 · M. Papinutto🇩🇪 · L. Scorzato🇩🇪 · S. Shcheredin🇩🇪 · A. Shindler🇩🇪 · C. Urbach🇩🇪 · U. Wenger🇩🇪 · I. Wetzorke🇩🇪

   We compare overlap fermions, which are chirally invariant, and Wilson twisted mass fermions in the approach to the chiral limit. Our quenched simulations reveal that with both formulations of lattice fermions pion masses of O(250 MeV) can be reached in practical simulations. Our comparison is done at a fixed lattice spacing a=0.123 fm. Several quantities are measured, such as hadron masses and pseudoscalar decay constants.

   hep-latNucl.Phys.B Proc.Suppl.(2005)·6 citations
10. 10*

    Light Hadron Spectrum, Renormalization Constants and Light Quark Masses with Two Dynamical Fermions

    D. Becirevic🇫🇷 · P. Boucaud🇫🇷 · V. Gimenez🇪🇸 · V. Lubicz🇮🇹 · G. Martinelli🇮🇹 · F. Mescia🇮🇹 · S. Simula🇮🇹 · C. Tarantino🇮🇹

    The results of a preliminary partially quenched (N_f=2) study of the light hadron spectrum, renormalization constants and light quark masses are presented. Numerical simulations are carried out with the LL-SSOR preconditioned Hybrid Monte Carlo with two degenerate dynamical fermions, using the plaquette gauge action and the Wilson quark action at beta = 5.8. Finite volume effects have been investigated employing two lattice volumes: 16^3 x 48 and 24^3 x 48. Configurations have been generated at four values of the sea quark mass corresponding to M_{PS}/M_V ~ 0.6 - 0.8.

    hep-lathep-phNucl.Phys.B Proc.Suppl.(2005)·6 citations
11. 11*

    Finite volume effects in chiral perturbation theory

    Gilberto Colangelo🇨🇭

    There has recently been an intense activity in the study of finite volume effects by means of chiral perturbation theory. In this contribution I review recent work in this field both for the epsilon-- (Mpi L \lesssim 1) and the p--regime (Mpi L \gg 1). For the latter I emphasize the importance of going beyond leading order calculations in chiral perturbation theory and the usefulness of asymptotic formulae a la L"uscher used in combination with CHPT.

    hep-latNucl.Phys.B Proc.Suppl.(2005)·27 citations
12. 12*

    Triviality and the Higgs mass lower bound

    K. Holland🇺🇸

    In the minimal Standard Model, it is commonly believed that the Higgs mass cannot be too small, otherwise Top quark dynamics makes the Higgs potential unstable. Although this Higgs mass lower bound is relevant for current phenomenology, we show that the Higgs vacuum instability in fact does not exist and only appears when treating incorrectly the cut-off in the renormalization of a trivial theory. We also demonstrate how to calculate correctly the regulator-dependent Higgs mass lower bound.

    hep-lathep-phNucl.Phys.B Proc.Suppl.(2005)·39 citations
13. 13*

    Quenching effects in strong penguin contributions to ${ϵ}^{\prime }/ϵ$

    Jack Laiho🇺🇸

    Quenching effects in strong penguin matrix elements are investigated. A lattice determination of ${\alpha }_q^{NS}$, the constant that appears in the quenched ChPT relevant for the lattice analysis of $K\to \pi \pi$ matrix elements, shows that this constant is large. The original RBC analysis of $Q_6$ matrix elements is revisited in light of this result. Also, the numerical effects of choosing the singlet Golterman-Pallante method of quenching $Q_6$ is investigated.

    hep-latNucl.Phys.B Proc.Suppl.(2005)·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.