HEP Lattice·hep-lat
18 papers—15 primary·3 cross-listed·reconstructed*
Emel Gulez · Christine Davies🇬🇧 · Alan Gray🇺🇸 · Peter Lepage🇺🇸 · Junko Shigemitsu🇺🇸 · Matthew Wingate🇺🇸
We study semileptonic B decays, using MILC dynamical configurations with . NRQCD heavy and AsqTad light quark actions are used. We obtain the semileptonic form factors and in the chiral limit.
Jozef Dudek🇺🇸 · Robert Edwards🇺🇸 · David Richards🇺🇸
The form factors for the radiative transitions between charmonium mesons are investigated. We employ an anisotropic lattice using a Wilson gauge action, and domain-wall fermion action. We extrapolate the form factors to , corresponding to a real photon, using quark-model-inspired functions. Finally, comparison is made with photocouplings extracted from the measured radiative widths, where known. Our preliminary results find photocouplings commensurate with these experimentally extracted values.
M. A. Clark🇺🇸 · Ph. de Forcrand🇨🇭 · A. D. Kennedy🇬🇧
We present initial results comparing the RHMC and R algorithms on large lattices with small quark masses using chiral fermions. We also present results concerning staggered fermions near the deconfinement/chiral phase transition. We find that the RHMC algorithm not only eliminates the step-size error of the R algorithm, but is also considerably more efficient. We discuss several possibilities for further improvement to the RHMC algorithm.
Weonjong Lee🇰🇷 · George T. Fleming🇺🇸
We present recent progress in understanding weak matrix elements on the lattice. We use HYP staggered fermions in quenched QCD to study numerically various properties of the amplitudes of the electroweak penguin operators and . We check chiral Ward identities to probe the validity of using improved staggered fermions in the calculation of weak matrix elements. We address the issue of mixing with unphysical lower dimension operators, which causes a divergent term in the case of the amplitudes. We propose a particular subtraction method as the best choice. We also measure the gold-plated ratio originally suggested by Becirevic and Villadoro.
Jon A. Bailey🇺🇸 · C. Bernard🇺🇸
Motivated by simulation results for octet and decuplet baryon masses using 2+1 flavors of light staggered quarks, we are incorporating staggered lattice artifacts into heavy baryon chiral perturbation theory, calculating the masses of various staggered baryons, and studying the connection between the staggered baryons of the chiral theory and the staggered baryons of simulations. We present order (m_q)^(3/2) loop contributions to the masses of several staggered nucleons and discuss interpolating fields that create these states.
Jongjeong Kim🇰🇷 · Taegil Bae🇰🇷 · Weonjong Lee🇰🇷
We present preliminary results of calculated using improved staggered fermions with the mixed action (valence quarks = HYP staggered fermions and sea quarks = AsqTad staggered fermions). We analyze the data based upon the prediction by Van de Water and Sharpe. A hint of consistency with the prediction is observed. We also present preliminary results of and .
Taegil Bae🇰🇷 · Jongjeong Kim🇰🇷 · Weonjong Lee🇰🇷
We investigate the effect of non-degenerate quarks on . This effect is noticeably large for (significantly larger than statistical uncertainty). Hence, it is important to include this effect in order to determine with higher precision. We also observe that the quality of fitting for gets better when we include non-degenerate combinations to fit to the prediction by Van de Water and Sharpe. However, this effect on and turns out to be relatively small.
A brief review is given of the lattice QCD calculation of the hadron spectrum. The status of current attempts toward inclusion of dynamical up, down and strange quarks is summarized focusing on our own work. Recent work on the possible existence of pentaquark states are assessed. We touch upon the PACS-CS Project for building our next machine for lattice QCD, and conclude with a near-term physics and machine prospects.
PACS-CS Collaboration : S. Aoki🇯🇵 · K.-I. Ishikawa · T. Ishikawa · N. Ishizuka🇯🇵 · K. Kanaya🇯🇵 · Y. Kuramashi🇯🇵 · M. Okawa🇯🇵 · K. Sasaki🇯🇵 · Y. Taniguchi🇯🇵 · N. Tsutsui🇯🇵 · A. Ukawa🇯🇵 · T. Yoshie
We describe our plan to develop a large-scale cluster system with a peak speed of 14.3Tflops for lattice QCD at the Center for Computational Sciences, University of Tsukuba, as a successor to the current 0.6Tflops CP-PACS computer. The system consist of 2560 nodes connected by a 16x16x10 three-dimensional hyper crossbar network. Each node has a single low-voltage 2.8GHz Xeon processor and 2GBytes of memory with 6.4GBytes/sec bandwidth, and 160 GBytes of disk in RAID1 mode. The network link in each of the three directions is made of dual Gigabit Ethernet with the peak throughput of 250MByte/sec. Hence each node has an aggregate network bandwidth of 750MByte/sec. The system will run under Linux and SCore, and an extension of the PM driver is developed for the network. The system will be developed jointly with Hitachi Limited. The installation is scheduled in the first quarter of Japanese Fiscal 2006 (April-June 2006) and the start of operation is expected in July 2006.
Leonardo Giusti (CERN)🇨🇭 · Silvia Necco (CPT)🇫🇷
The low-mode averaging technique is a powerful tool for reducing large fluctuations in correlation functions due to low-mode eigenvalues of the Dirac operator. In this work we propose a generalization to baryons and test our method on two-point correlation functions of left-handed nucleons, computed with quenched Neuberger fermions on a lattice with extension L=1.5 fm. We show that the statistical fluctuations can be reduced and the baryon signal significantly improved.
M. D'Elia🇮🇹 · A. Di Giacomo🇮🇹 · C. Pica🇮🇹
QCD with N_f=2 is a specially interesting system to investigate the chiral transition. The order of the transition has still not been established. We report the results of an in-depth numerical investigation performed with staggered fermions on lattices with L_t=4 and L_s=12,16,20,24,32 and quark masses am_q ranging from 0.01335 to 0.307036. Using finite-size techniques we compare the scaling behavior of a number of thermodynamical susceptibilities with the expectations of O(4) and O(2) universality classes. Clear disagreement is observed. Indications of a first order transition are found.
The question of the role of the center of the gauge group in the phenomenon of confinement in Yang-Mills theory is addressed. The investigation is performed from the most general perspective of considering all possible choices for the gauge symmetry group. In this context, an interesting role is played by G(2) Yang-Mills theory: the simplest pure gauge theory with a trivial center and without 't Hooft flux vortices. Numerical simulations show the presence of a first order finite temperature deconfinement phase transition in G(2) Yang-Mills theory in (3+1) dimensions. Interestingly, the G(2) gauge symmetry can be broken to an SU(3) subgroup by the Higgs mechanism. We investigate the relation between the deconfinement phase transition in G(2) and SU(3) Yang-Mills theories by numerical simulations in the G(2) gauge-Higgs system.
D. Becirevic🇫🇷 · B. Blossier🇫🇷 · Ph. Boucaud🇫🇷 · V. Gimenez🇪🇸 · V. Lubicz🇮🇹 · F. Mescia🇮🇹 · S. Simula🇮🇹 · C. Tarantino🇮🇹
We present results for the light quark masses obtained from a lattice QCD simulation with N_f=2 degenerate Wilson dynamical quark flavours. The sea quark masses of our lattice, of spacing a ~ 0.06 fm, are relatively heavy, i.e., they cover the range corresponding to 0.60 <~ M_P/M_V <~ 0.75. After implementing the non-perturbative RI-MOM method to renormalise quark masses, we obtain m_{ud}^{MS}(2 GeV)=4.3 +- 0.4^{+1.1}_{-0} MeV, and m_s^{MS}(2 GeV)=101 +- 8^{+25}_{-0} MeV, which are about 15% larger than they would be if renormalised perturbatively. In addition, we show that the above results are compatible with those obtained in a quenched simulation with a similar lattice.
Walter Wilcox🇺🇸 · Dean Darnell🇺🇸 · Ron Morgan🇺🇸 · Randy Lewis🇨🇦
We give a general introduction and discussion of the issues involved in using the twisted mass formulation of lattice fermions in the context of disconnected loop calculations, including a short orientation on the present experimental situation for nucleon strange quark form factors. A prototype calculation of the disconnected part of the nucleon scalar form factor is described.
R. Morrin🇮🇪 · M. Peardon🇮🇪 · S.M. Ryan🇮🇪
We present methods and results for the tuning of quark and gluon anisotropies for improved actions in N_f = 2 QCD.
L.Ya.Glozman (Univ. Graz)🇦🇹 · A.V.Nefediev (ITEP, Moscow)🇷🇺 · J.E.F.T.Ribeiro (IST, Lisbon)🇵🇹
In this paper, we discuss the transition to the semiclassical regime in excited hadrons, and consequently, the restoration of chiral symmetry for these states. We use a generalised Nambu-Jona-Lasinio model with the interaction between quarks in the form of the instantaneous Lorentz-vector confining potential. This model is known to provide spontaneous breaking of chiral symmetry in the vacuum via the standard selfenergy loops for valence quarks. It has been shown recently that the effective single-quark potential is of the Lorentz-scalar nature, for the low-lying hadrons, while, for the high-lying states, it becomes a pure Lorentz vector and hence the model exhibits the restoration of chiral symmetry. We demonstrate explicitly the quantum nature of chiral symmetry breaking, the absence of chiral symmetry breaking in the classical limit as well as the transition to the semiclassical regime for excited states, where the effect of chiral symmetry breaking becomes only a small correction to the classical contributions.
We construct a supersymmetry and global symmetry preserving deformation of the type IIB matrix model. This model, without orbifold projection, serves as a nonperturbative regularization for supersymmetric Yang-Mills theory in four Euclidean dimensions. Upon deformation, the eigenvalues of the bosonic matrices are forced to reside on the surface of a hypertorus. We explicitly show the relation between the noncommutative moduli space of the deformed matrix theory and the Brillouin zone of the emergent lattice theory. This observation makes the transmutation of the moduli space into the base space of target field theory clearer. The lattice theory is slightly nonlocal, however the nonlocality is suppressed by the lattice spacing. In the classical continuum limit, we recover the SYM theory. We also discuss the result in terms of D-branes and interpret it as collective excitations of D(-1) branes forming D3 branes.
T.S.Biro🇭🇺 · G.Purcsel🇭🇺 · G.Gyorgyi🇭🇺 · A.Jakovac🇭🇺 · Zs.Schram🇭🇺
We propose that power-law tailed hadron spectra may be viewed as stemming from a matter in an unconventional equilibrium state typical for non-extensive thermodynamics. A non-extensive Boltzmann equation, which is able to form such spectra as a stationary solution, is utilized as a rough model of quark matter hadronization. Basic ideas about non-extensive simulation of the QCD equation of state on the lattice are presented.
* 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.