10,998 research outputs found
Recent developments in chiral gauge theories: Approach of infinitely many fermi fields
I present the recent developments in a specific sub-field of chiral gauge
theories on the lattice. This sub-field pertains to the use of infinitely many
fermi fields to describe a single chiral field. In this approach, both
anomalous and anomaly free theories can be discussed in equal footing. It
produces the correct anomaly in the continuum limit. It has the potential to
describe fermion number violating processes in the presence of a gauge field
background with non-trivial topological charge on a finite lattice.Comment: 6 TeX pages: 6; Latex file, needs espcrc2.sty which is attache
Overlap formulation of Majorana--Weyl fermions
An overlap method for regularizing Majorana--Weyl fermions interacting with
gauge fields is presented. A mod(2) index is introduced in relation to the
anomalous violation of a discrete global chiral symmetry. Most of the paper is
restricted to 2 dimensions but generalizations to 2+8k dimensions should be
straightforward.Comment: 8 pages, Plain Te
Massless Composite Fermions in Two Dimensions and the Overlap
There exist chiral gauge models in two dimensions that have massless
composite fermions. Two examples are presented and it is suggested that they be
accepted as benchmark test-cases for generic proposals of non-perturbatively
regulating chiral gauge theories in any dimension. We apply the overlap to the
simpler of the two benchmarks and present the results of a numerical simulation
of modest size.Comment: 12 pages, Plain TeX with epsf, 2 PS figure
Gribov Copy and Complex Phase of Chiral Determinant
We calculate the complex phase of chiral determinant by the vacuum overlap
formula with configurations of two-dimensional U(1) gauge field fixed in Landau
and Laplacian gauge. The complex phase fluctuates over the Gribov copies, which
appear in the process of Landau gauge fixing and contain vortex-like
singularities. In the Laplacian gauge, the fluctuation can be reduced and the
phase can be determined uniquely. If it is used as a preconditioning for Landau
gauge fixing, the most smooth configuration is obtained among the copies
generated.Comment: Talk presented at LATTICE96(chiral gauge), 3 LaTeX pages with 5
postscript figures, need espcrc2.sty(included
Interacting staggered domain wall fermions
The behavior of staggered domain wall fermions in the presence of gauge
fields is presented. In particular, their response to gauge fields with
nontrivial topology is discussed.Comment: Lattice2002(Chiral) proceedings, LaTeX, 3 pages 2 eps figure
A numerical test of the continuum index theorem on the lattice
The overlap formalism of chiral fermions provides a tool to measure the
index, Q, of the chiral Dirac operator in a fixed gauge field background on the
lattice. This enables a numerical measurement of the probability distribution,
p(Q), in Yang-Mills theories. We have obtained an estimate for p(Q) in pure
SU(2) gauge theory by measuring Q on 140 independent gauge field configurations
generated on a 12^4 lattice using the standard single plaquette Wilson action
at a coupling of beta=2.4. This distribution is in good agreement with a recent
measurement [8] of the distribution of the topological charge on the same
lattice using the same coupling and the same lattice gauge action. In
particular we find =3.3(4) to be compared with = 3.9(5) found in
[8]. The good agreement between the two distributions is an indication that the
continuum index theorem can be carried over in a probabilistic sense on to the
lattice.Comment: 17 pages, 5 figures, plain TeX, uses eps
Large N QCD -- Continuum reduction
Numerical evidence combined with Eguchi-Kawai reduction indicate that there
are no finite volumes effects in the large N limit of QCD as long as the linear
extent of the four-torus is bigger than a critical size. This is referred to as
continuum reduction. Since fermions in the fundamental representation are
naturally quenched in the large N limit, as long as we only have a finite
number of flavors, continuum reduction provides us with the exciting
possibility to numerically solve large N QCD using chiral fermions and present
day computers.Comment: 7 pages, 11 figures, uses espcrc2.sty file, contribution to the
LHP2003 workshop held in Cairns, Australi
A simulation of the Schwinger model in the overlap formalism
In the continuum, the single flavor massless Schwinger model has an exact
global axial symmetry in the sector of perturbative gauge fields. This
symmetry is explicitly broken by gauge fields with nonzero topological charge
inducing a nonzero expectation value for the bilinear . We show
that a lattice formulation of this model, using the overlap formalism to treat
the massless fermions, explicitly exhibits this phenomenon. A Monte Carlo
simulation of the complete system yields the correct value of the fermion
condensate and shows unambiguously that it originates from the sector of
topological charge equal to unity.Comment: Plain TeX file, 9 pages
Evidence for fractional topological charge in SU(2) pure Yang-Mills theory
We investigate the spectral flows of the hermitian Wilson-Dirac operator in
the fundamental and adjoint representations on two ensembles of pure SU(2)
gauge field configurations at the same physical volume. We find several
background gauge field configurations where the index of the hermitian
Wilson-Dirac operator in the adjoint representation is not four times the index
in the fundamental representation. This could imply a topological basis for the
gluino condensate in supersymmetric Yang-Mills theories.Comment: 6 pages latex with 1 postscript figure included by eps
Investigation of temperature and concentration oscillations in the directional solidification of Pb-Sn-Te
Directional solidification of the pseudobinary compound semiconductor material Pb sub 1-x Sn sub x Te by the Bridgman crystal growth process will be studied. Natural convection in the molten sample will be visualized with a novel electrochemical cell technique that employs the solid electrolyte material yttria-stabilized zirconia. Mass transfer by both diffusion and convection will be measured by detecting the motion of oxygen tracer in the liquid. Additional applications for electrochemical cells in semiconductor crystal growth are suggested. Unsteady convection in the melt will also be detected by the appearance of temperature oscillations. The purpose of this study is to experimentally characterize the overstable conditions for a Pb sub 1-x Sn sub x Te melt in the vertical Bridgman crystal growth technique and use a linear analysis to predict the onset of convection for this system
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