756 research outputs found
Quantum Link Models with Many Rishon Flavors and with Many Colors
Quantum link models are a novel formulation of gauge theories in terms of
discrete degrees of freedom. These degrees of freedom are described by quantum
operators acting in a finite-dimensional Hilbert space. We show that for
certain representations of the operator algebra, the usual Yang-Mills action is
recovered in the continuum limit. The quantum operators can be expressed as
bilinears of fermionic creation and annihilation operators called rishons.
Using the rishon representation the quantum link Hamiltonian can be expressed
entirely in terms of color-neutral operators. This allows us to study the large
N_c limit of this model. In the 't Hooft limit we find an area law for the
Wilson loop and a mass gap. Furthermore, the strong coupling expansion is a
topological expansion in which graphs with handles and boundaries are
suppressed.Comment: Lattice2001(theorydevelop), poster by O. Baer and talk by B.
Schlittgen, 6 page
Gauge and matter fields as surfaces and loops - an exploratory lattice study of the Z(3) Gauge-Higgs model
We discuss a representation of the Z(3) Gauge-Higgs lattice field theory at
finite density in terms of dual variables, i.e., loops of flux and surfaces. In
the dual representation the complex action problem of the conventional
formulation is resolved and Monte Carlo simulations at arbitrary chemical
potential become possible. A suitable algorithm based on plaquette occupation
numbers and link-fluxes is introduced and we analyze the model at zero
temperature and finite density both in the weak and strong coupling phases. We
show that at zero temperature the model has different first order phase
transitions as a function of the chemical potential both for the weak and
strong coupling phases. The exploratory study demonstrates that alternative
degrees of freedom may successfully be used for Monte Carlo simulations in
several systems with gauge and matter fields.Comment: Typos corrected and some statements refined. Final version to appear
in Phys. Rev.
Non-perturbative Renormalization Constants using Ward Identities
We extend the application of vector and axial Ward identities to calculate
, and , coefficients that give the mass dependence of the
renormalization constants of the corresponding bilinear operators in the
quenched theory. The extension relies on using operators with non-degenerate
quark masses. It allows a complete determination of the improvement
coefficients for bilinears in the quenched approximation using Ward Identities
alone. Only the scale dependent normalization constants (or )
and are undetermined. We present results of a pilot numerical study using
hadronic correlators.Comment: 3 pages. Makefile and sources included. Talk presented at LATTICE98
(matrixelement
Topological Phases in Neuberger-Dirac operator
The response of the Neuberger-Dirac fermion operator D=\Id + V in the
topologically nontrivial background gauge field depends on the negative mass
parameter in the Wilson-Dirac fermion operator which enters
through the unitary operator . We classify
the topological phases of by comparing its index to the topological charge
of the smooth background gauge field. An exact discrete symmetry in the
topological phase diagram is proved for any gauge configurations. A formula for
the index of D in each topological phase is derived by obtaining the total
chiral charge of the zero modes in the exact solution of the free fermion
propagator.Comment: 27 pages, Latex, 3 figures, appendix A has been revise
Kosterlitz-Thouless Universality in a Fermionic System
A new extension of the attractive Hubbard model is constructed to study the
critical behavior near a finite temperature superconducting phase transition in
two dimensions using the recently developed meron-cluster algorithm. Unlike
previous calculations in the attractive Hubbard model which were limited to
small lattices, the new algorithm is used to study the critical behavior on
lattices as large as . These precise results for the first time
show that a fermionic system can undergo a finite temperature phase transition
whose critical behavior is well described by the predictions of Kosterlitz and
Thouless almost three decades ago. In particular it is confirmed that the
spatial winding number susceptibility obeys the well known predictions of
finite size scaling for and up to logarithmic corrections the pair
susceptibility scales as at large volumes with for .Comment: Revtex format; 4 pages, 2 figure
Dynamical lattice QCD thermodynamics with domain wall fermions
We present results from simulations of two flavor QCD thermodynamics at N_t=4
with domain wall fermions. In contrast to other lattice fermion formulations,
domain wall fermions preserve the full chiral symmetry of the continuum at
finite lattice spacing (up to terms exponentially small in an extra parameter).
Just above the phase transition, we find that the axial U(1) symmetry is broken
only by a small amount. We discuss an ongoing calculation to determine the
order and properties of the phase transition using domain wall fermions, since
the global symmetries of the theory are expected to be important here.Comment: 4 pages, 4 eps figures, LaTeX. To appear in the Proceedings of the
XVth Particles and Nuclei International Conference (PANIC '99), Uppsala,
Sweden, 10-16 June 199
The Color-Flavor Transformation and Lattice QCD
We present the color-flavor transformation for gauge group SU(N_c) and
discuss its application to lattice QCD.Comment: 6 pages, Lattice2002(theoretical), typo in Ref.[1] correcte
Fermion loop simulation of the lattice Gross-Neveu model
We present a numerical simulation of the Gross-Neveu model on the lattice
using a new representation in terms of fermion loops. In the loop
representation all signs due to Pauli statistics are eliminated completely and
the partition function is a sum over closed loops with only positive weights.
We demonstrate that the new formulation allows to simulate volumes which are
two orders of magnitude larger than those accessible with standard methods
Dirac eigenvalues and eigenvectors at finite temperature
We investigate the eigenvalues and eigenvectors of the staggered Dirac
operator in the vicinity of the chiral phase transition of quenched SU(3)
lattice gauge theory. We consider both the global features of the spectrum and
the local correlations. In the chirally symmetric phase, the local correlations
in the bulk of the spectrum are still described by random matrix theory, and we
investigate the dependence of the bulk Thouless energy on the simulation
parameters. At and above the critical point, the properties of the low-lying
Dirac eigenvalues depend on the -phase of the Polyakov loop. In the real
phase, they are no longer described by chiral random matrix theory. We also
investigate the localization properties of the Dirac eigenvectors in the
different -phases.Comment: Lattice 2000 (Finite Temperature), 5 page
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