553 research outputs found
The Schr\"odinger Functional for Improved Gluon and Quark Actions
The Schr\"odinger Functional (quantum/lattice field theory with Dirichlet
boundary conditions) is a powerful tool in the non-perturbative improvement and
for the study of other aspects of lattice QCD. Here we adapt it to improved
gluon and quark actions, on isotropic as well as anisotropic lattices.
Specifically, we describe the structure of the boundary layers, obtain the
exact form of the classically improved gauge action, and outline the
modifications necessary on the quantum level. The projector structure of
Wilson-type quark actions determines which field components can be specified at
the boundaries. We derive the form of O(a) improved quark actions and describe
how the coefficients can be tuned non-perturbatively. There is one coefficient
to be tuned for an isotropic lattice, three in the anisotropic case.
Our ultimate aim is the construction of actions that allow accurate
simulations of all aspects of QCD on coarse lattices.Comment: 39 pages, LaTeX, 11 embedded eps file
QCD String Spectrum 2002
Results from a comprehensive new analysis on the excitation spectrum of the
QCD string are presented. A rapid onset of string formation is observed in the
spectrum on a length scale of 2 fm, with Dirichlet boundary conditions. The
crossover from the short distance spectrum towards string excitations and an
observed fine structure in the 1--3 fm range are related to effective string
theory. The deficiencies of the Nambu-Goto bosonic string model in describing
the observed spectrum are briefly discussed.Comment: Lattice2002(topology), 3 pages, 2 figure
Study of unstable particle through the spectral function in O(4) theory
We test application of the maximum entropy method to decompose the states
contributing to the unstable correlation function through the spectral
function in the four dimensional O(4) theory. Reliable results are
obtained for the mass and two-particle state energy using
only the correlation function. We also find that the property of the
particle is different between the unstable ()
and stable () cases.Comment: Lattice2002(spectrum), 3 page
CP breaking in lattice chiral gauge theory
The CP symmetry is not manifestly implemented for the local and doubler-free
Ginsparg-Wilson operator in lattice chiral gauge theory. We precisely identify
where the effects of this CP breaking appear.Comment: 3 pages, Lattice2002(chiral
A non-perturbative determination of Z_V and b_V for O(a) improved quenched and unquenched Wilson fermions
By considering the local vector current between nucleon states and imposing
charge conservation we determine, for improved Wilson fermions, its
renormalisation constant and quark mass improvement coefficient. The
computation is performed for both quenched and two flavour unquenched fermions.Comment: 3 pages, 4 figures, Lattice(2002)(improve
Non-perturbative determination of Z_A^{stat} in quenched QCD
We non-perturbatively calculate the renormalization factor of the static
axial vector current in O(a) improved quenched lattice QCD. Its scale
dependence is mapped out in the Schroedinger functional scheme by means of a
recursive finite-size scaling technique, taking the continuum limit in each
step. We also obtain Z_A^{stat} for Wilson fermions in order to renormalize
existing unimproved data on F_B^{bare} non-perturbatively.Comment: Lattice2002(heavyquark), 3 pages, latex2e, 5 Postscript figures, uses
epsfig, amssymb and espcrc
A scalable PC-based parallel computer for lattice QCD
A PC-based parallel computer for medium/large scale lattice QCD simulations
is suggested. The Eotvos Univ., Inst. Theor. Phys. cluster consists of 137
Intel P4-1.7GHz nodes. Gigabit Ethernet cards are used for nearest neighbor
communication in a two-dimensional mesh. The sustained performance for
dynamical staggered(wilson) quarks on large lattices is around 70(110) GFlops.
The exceptional price/performance ratio is below $1/Mflop.Comment: 3 pages, 2 figures, Lattice2002(machines
Finite size effects on in QCD from Chiral Perturbation Theory
We present a determination of the shift due to the finite
spatial box size by means of Chiral Perturbation Theory and
L\"uscher's formula. The range of applicability of the chiral prediction is
discussed.Comment: 3 pages, 3 figures, Lattice2002(spectrum
A Study of Charmonium Systems across the Deconfinement Transition
We present results from lattice studies of charmonium systems near the
deconfinement transition temperature. On quenched isotropic lattices with
lattice spacings between 0.02 and 0.05 fm, bar{q} q systems with quark masses
close to the charm mass and with different spin-parity quantum numbers are
studied in the temperature range 0.9 Tc - 3 Tc. Results for temporal
correlators of local operators, and the spectral functions constructed from
them, are discussed. For the pseudoscalar and vector channels, the correlators
are observed to change very little across the deconfinement transition, unlike
in the case of the light quarks.Comment: 3 pages, 4 figures, Lattice2002(nonzerot
Hamiltonian study of Supersymmetric Yang-Mills Quantum Mechanics
New results obtained within the recently developed approach to supersymmetric
quantum mechanical systems are presented. The method does not suffer from the
sign problem in any dimensions and is capable to provide any quantum observable
with controllable systematic error. Discussed results include: the spectrum and
Witten index of the D=4 system, and the spectrum of zero volume glueballs in
higher 3 < D < 11 dimensions.Comment: 4 pages, 3 figures, contribution to Lattice200
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