317 research outputs found
Gross-Witten-Wadia transition in a matrix model of deconfinement
We study the deconfining phase transition at nonzero temperature in a SU(N)
gauge theory, using a matrix model which was analyzed previously at small N. We
show that the model is soluble at infinite N, and exhibits a Gross-Witten-Wadia
transition. In some ways, the deconfining phase transition is of first order:
at a temperature , the Polyakov loop jumps discontinuously from 0 to1/2,
and there is a nonzero latent heat . In other ways, the transition is
of second order: e.g., the specific heat diverges as
when . Other critical exponents satisfy the usual scaling
relations of a second order phase transition. In the presence of a nonzero
background field for the Polyakov loop, there is a phase transition at the
temperature where the value of the loop =1/2, with . Since
as , this
transition is of third order.Comment: 7pages, 1 figure; discussion on matrix models is extended; references
are adde
Topological structure of the SU(3) vacuum and exceptional eigenmodes of the improved Wilson-Dirac operator
We present a study of the instanton size and spatial distributions in pure
SU(3) gauge theory using under-relaxed cooling. We also investigate the
low-lying eigenmodes of the (improved) Wilson-Dirac operator, in particular,
the appearance of zero-modes and their space-time localisation with respect to
instantons in the underlying gauge field.Comment: Contribution to Lattice97 proceedings: 3 pages, LaTeX2e, 4 postscript
figures, uses espcrc2.st
Development of satisfactory lateral- directional handling qualities in the landing approach
Developing lateral stability and directional control handling qualities in landing approach control of aircraf
Static Potential and Local Color Fields in Unquenched Three-Dimensional Lattice QCD
String breaking by dynamical quarks in (2+1)-d lattice QCD is demonstrated in
this project, by measuring the static potential and the local color-electric
field strength between a heavy quark and antiquark pair at large separations.
Simulations are done for unquenched SU(2) color with two flavors of staggered
quarks. An improved gluon action is used which allows simulations to be done on
coarse lattices, providing an extremely efficient means to access the quark
separations and propagation times at which string breaking occurs. The static
quark potential is extracted using only Wilson loop operators and hence no
valence quarks are present in the trial states. Results give unambiguous
evidence for string breaking as the static quark potential completely saturates
at twice the heavy-light meson mass at large separations. It is also shown that
the local color-electric field strength between the quark pair tends toward
vacuum values at large separations. Implications of these results for
unquenched simulations of QCD in 4-d are drawn.Comment: 3 pages, contribution to Lattice 2002 proceedings (Confinement
Improved lattice operators: the case of the topological charge density
We analyze the properties of a class of improved lattice topological charge
density operators, constructed by a smearing-like procedure. By optimizing the
choice of the parameters introduced in their definition, we find operators
having (i) a better statistical behavior as estimators of the topological
charge density on the lattice, i.e. less noisy; (ii) a multiplicative
renormalization much closer to one; (iii) a large suppression of the
perturbative tail (and other unphysical mixings) in the corresponding lattice
topological susceptibility.Comment: 11 pages (REVTEX) + 4 (uuencoded) figure
Improvement, dynamical fermions, and heavy quark screening in QCD_3
First results from simulations of improved actions for both gauge fields and
staggered fermion fields in three dimensional QCD are presented. This work
provides insight into some issues of relevance to lattice theories in four
dimensions. In particular, the renormalization of the bare lattice coupling is
dramatically reduced when the tree-level improved action is used. Naik
improvement of the staggered fermion action produces little reduction in
scaling violations of the rho meson mass. String breaking in the heavy quark
potential in the unquenched theory is also clearly resolved, using Wilson loops
to bound the ground state energy.Comment: LATTICE98(improvement), 3 pages, 3 figures (psfig format
On the screening of the potential between adjoint sources in
We calculate the potential between adjoint sources in pure gauge
theory in three dimensions. We investigate whether the potential saturates at
large separations due to the creation of a pair of gluelumps, colour-singlet
states formed when glue binds to an adjoint source.Comment: 3 pages, uuencoded Z-compressed postscript file, contribution to
Lattice '9
``GLUELUMP'' SPECTRUM AND ADJOINT SOURCE POTENTIAL IN LATTICE QCD
We calculate the potential between ``quarks'' which are in the adjoint
representation of SU(2) color in the three-dimensional lattice theory. We work
in the scaling region of the theory and at large quark separations . We also
calculate the masses of color-singlet bound states formed by coupling
an adjoint quark to adjoint glue (``gluelumps''). Good scaling behavior is
found for the masses of both magnetic (angular momentum ) and electric
() gluelumps, and the magnetic gluelump is found to be the lowest-lying
state. It is naively expected that the potential for adjoint quarks should
saturate above a separation where it becomes energetically
favorable to produce a pair of gluelumps. We obtain a good estimate of the
naive screening distance . However we find little evidence of
saturation in the potential out to separations of about twice .Comment: 8 pages plus 8 figures in 2 postscript files (uuencoded
Development of automatic and manual flight director landing systems for the XV-15 tilt rotor aircraft in helicopter mode
The objective of this effort is to determine IFR approach path and touchdown dispersions for manual and automatic XV-15 tilt rotor landings, and to develop missed approach criteria. Only helicopter mode XV-15 operation is considered. The analysis and design sections develop the automatic and flight director guidance equations for decelerating curved and straight-in approaches into a typical VTOL landing site equipped with an MLS navigation aid. These system designs satisfy all known pilot-centered, guidance and control requirements for this flying task. Performance data, obtained from nonstationary covariance propagation dispersion analysis for the system, are used to develop the approach monitoring criteria. The autoland and flight director guidance equations are programmed for the VSTOLAND 1819B digital computer. The system design dispersion data developed through analysis and the 1819B digital computer program are verified and refined using the fixed-base, man-in-the-loop XV-15 VSTOLAND simulation
Gribov Copies in the Maximally Abelian Gauge and Confinement
We fix lattice gauge fields to the Maximally Abelian gauge in both
three and four dimensions. We extract the corresponding fields and
monopole current densities and calculate separately the confining string
tensions arising from these fields and monopole `condensates'. We
generate multiple Gribov copies and study how the fields and monopole
distributions vary between these different copies. As expected, we find
substantial variations in the number of monopoles, their locations and in the
values of the field strengths. The string tensions extracted from
`extreme' Gribov copies also differ but this difference appears to be no more
than about 20\%. We also directly compare the fields of different Gribov
copies. We find that on the distance scales relevant to confinement the
and monopole fluxes that disorder Wilson loops are highly correlated between
these different Gribov copies. All this suggests that while there is indeed a
Gribov copy problem the resulting ambiguity is, in this gauge and for the study
of confinement, of limited importance.Comment: 31 pages LaTeX plus 5 PostScript figures. Uses epsf.sty.
Self-unpacking, uuencoded tar-compressed fil
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