260 research outputs found
New findings for topological excitations in SU(3) lattice gauge theory
We probe the SU(3) vacuum using eigenvectors of the Dirac operator with an
arbitrary phase for the temporal boundary condition. We consider configurations
with topological charge |Q| = 1 near the QCD phase transition and at low
temperatures on a torus. For all our ensembles we show that the zero-mode of
the Dirac operator changes its position as one changes the phase of the
boundary condition. For ensembles near the QCD phase transition our results
closely resemble the behavior of zero-modes for Kraan - van Baal solutions of
the classical Yang-Mills equations where the individual lumps are interpreted
as monopoles. Our findings near T_c and on the torus show that for both cases
an excitation with topological charge |Q| = 1 is built from several separate
lumps.Comment: Typo corrected. To appear in Nuclear Physics
Calorons, instantons and constituent monopoles in SU(3) lattice gauge theory
We analyze the zero-modes of the Dirac operator in quenched SU(3) gauge
configurations at non-zero temperature and compare periodic and anti-periodic
temporal boundary conditions for the fermions. It is demonstrated that for the
different boundary conditions often the modes are localized at different
space-time points and have different sizes. Our observations are consistent
with patterns expected for Kraan - van Baal solutions of the classical
Yang-Mills equations. These solutions consist of constituent monopoles and the
zero-modes are localized on different constituents for different boundary
conditions. Our findings indicate that the excitations of the QCD vacuum are
more structured than simple instanton-like lumps.Comment: Remarks added. To appear in Phys. Rev.
Two-particle wave function in four dimensional Ising model
An exploratory study of two-particle wave function is carried out with a four
dimensional simple model. The wave functions not only for two-particle ground
and first excited states but also for an unstable state are calculated from
three- and four-point functions using the diagonalization method suggested by
L\"uscher and Wolff. The scattering phase shift is evaluated from these wave
functions.Comment: Poster presented at Lattice2004(spectrum), Fermilab, June 21-26, 200
Testing the self-duality of topological lumps in SU(3) lattice gauge theory
We discuss a simple formula which connects the field-strength tensor to a
spectral sum over certain quadratic forms of the eigenvectors of the lattice
Dirac operator. We analyze these terms for the near zero-modes and find that
they give rise to contributions which are essentially either self-dual or anti
self-dual. Modes with larger eigenvalues in the bulk of the spectrum are more
dominated by quantum fluctuations and are less (anti) self-dual. In the high
temperature phase of QCD we find considerably reduced (anti) self-duality for
the modes near the edge of the spectral gap.Comment: Remarks added, to appear in Phys. Rev. Let
Preliminary results of the heavy-light meson spectrum using chirally improved light quarks
Using a ``wall'' of quark point sources, we invert the chirally improved
Dirac operator to create an ``incoherent'' collection of quark propagators
which originate from all spatial points of the source time slice. The
lowest-order NRQCD approximation is used to create heavy-quark propagators from
the same wall source. However, since the numerical cost involved in computing
such heavy-quark propagators is low, we are able to use a number of source
gauge paths to establish coherence between the heavy and light quarks at
several spatial separations. The resulting collection of heavy-light meson
correlators is analyzed to extract the corresponding mass spectrum.Comment: 3 pages, 1 figure, Lattice2004(spectrum), minor corrections adde
Setting the scale for the Luescher-Weisz action
We study the quark-antiquark potential of quenched SU(3) lattice gauge theory
with the Luescher-Weisz action. After blocking the gauge fields with the
recently proposed hypercubic transformation we compute the Sommer parameter,
extract the lattice spacing a and set the scale at 6 different values of the
gauge coupling in a range from a = 0.084 fm to 0.136 fm.Comment: Remarks and references added, to appear in Phys. Rev.
Doubly Periodic Instanton Zero Modes
Fermionic zero modes associated with doubly periodic SU(2) instantons of unit
charge are considered. In cases where the action density exhibits two
`instanton cores' the zero mode peaks on one of four line-segments joining the
two constituents. Which of the four possibilities is realised depends on the
fermionic boundary conditions; doubly periodic, doubly anti-periodic or mixed.Comment: 12 pages, 4 figure
Lattice Regularization of the Chiral Schwinger Model
We analyze the chiral Schwinger model on an infinite lattice using the
continuum definition of the fermion determinant and a linear interpolation of
the lattice gauge fields. For non-compact and Wilson formulation of the gauge
field action it is proven that the effective lattice model is
Osterwalder-Schrader positive, which is a sufficient condition for the
reconstruction of a physical Hilbert space from the model defined on a
Euclidean lattice. For the non-compact model we furthermore establish the
existence of critical points where the corresponding continuum theory can be
reconstructed. We show that the continuum limit for the two-point functions of
field strength and chiral densities can be controlled analytically. The article
ends with some remarks on fermionic observables.Comment: 18 page
Chiral symmetry restoration and the Z3 sectors of QCD
Quenched SU(3) lattice gauge theory shows three phase transitions, namely the
chiral, the deconfinement and the Z3 phase transition. Knowing whether or not
the chiral and the deconfinement phase transition occur at the same temperature
for all Z3 sectors could be crucial to understand the underlying microscopic
dynamics. We use the existence of a gap in the Dirac spectrum as an order
parameter for the restoration of chiral symmetry. We find that the spectral gap
opens up at the same critical temperature in all Z3 sectors in contrast to
earlier claims in the literature.Comment: 4 pages, 4 figure
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