104 research outputs found
Hadron correlators with improved fermions
We investigate point-to-point correlation functions for various mesonic and
baryonic channels using the -improved Wilson action due to
Sheikholeslami and Wohlert. We consider propagators to both time slices 0 and
1. We find that discretisation effects are more pronounced than those reported
with unimproved Wilson fermions, but that the same procedure for removing
finite size effects is successful. Extrapolating to the chiral limit, we see
the notable features predicted phenomenologically: the ratio of interacting to
free correlators in the vector channel is roughly constant to about 1 fm, while
in the pseudoscalar channel the ratio increases markedly due to the strong
binding.Comment: Talk at Lattice '94: 3 pages, latex using espcrc2 and epsf with 4
tar'd and feathered PS figures appended in self-extracting shell archive.
PostScript file available on the WorldWide Web as
http://python.swan.ac.uk/~pypeters/p2pbiel.p
Properties of the non-Gaussian fixed point in 4D compact U(1) lattice gauge theory
We examine selected properties of the gauge-ball spectrum and fermionic
variables in the vicinity of the recently discussed non-Gaussian fixed point of
4D compact U(1) lattice gauge theory within the quenched approximation.
Approaching the critical point from within the confinement phase, our data
support scaling of gauge-ball states in units of the string tension
square root. The analysis of the chiral condensate within the framework of a
scaling form for the equation of state suggests non mean-field values for the
magnetic exponents and .Comment: 73K postscript fil
Topological properties of full QCD at the phase transition
We investigate the topological properties of the QCD vacuum with 4 flavours
of dynamical staggered fermions at finite temperature. To calculate the
topological susceptibility we use the field-theoretical method. As in the
quenched case, a sharp drop is observed for the topological susceptibility
across the phase transition.Comment: LATTICE98(confine
Scaling of gauge balls and static potential in the confinement phase of the pure U(1) lattice gauge theory
We investigate the scaling behaviour of gauge-ball masses and static
potential in the pure U(1) lattice gauge theory on toroidal lattices. An
extended gauge field action is used with and -0.5. Gauge-ball correlation
functions with all possible lattice quantum numbers are calculated. Most
gauge-ball masses scale with the non-Gaussian exponent .
The gauge-ball mass scales with the Gaussian value in the investigated range of correlation lengths. The static potential is
examined with Sommer's method. The long range part scales consistently with
but the short range part tends to yield smaller values of . The
-function, having a UV stable zero, is obtained from the running
coupling. These results hold for both values, supporting universality.
Consequences for the continuum limit of the theory are discussed.Comment: Contribution to the Lattice 97 proceedings, LaTeX, 3 pages, 3 figure
Breaking of the adjoint string in 2+1 dimensions
The roughly linear rise of the potential found between adjoint sources in
SU(N) in lattice simulations is expected to saturate into a state of two
`gluelumps' due to gluonic screening. We examine this in SU(2) in 2+1
dimensions. Crossover between string-like and broken states is clearly seen by
the mixing-matrix technique, using different operators to probe the two states;
the breaking behaviour is rather abrupt. Furthermore, we are able to show that
both types of operator have a finite overlap with both states; in the case of
the Wilson loops the overlap with the broken string is, as predicted, very
small.Comment: LaTeX2e, 20 pages, 15 figures with epsfig; uses amstex, amssymb,
a4wide; minor change to presentation (notation for operators) onl
Universality of the gauge-ball spectrum of the four-dimensional pure U(1) gauge theory
We continue numerical studies of the spectrum of the pure U(1) lattice gauge
theory in the confinement phase, initiated in our previous work. Using the
extended Wilson action we address the question of universality of the phase
transition line in the () plane between the confinement and the
Coulomb phases. Our present results at for the gauge-ball
spectrum are fully consistent with the previous results obtained at . Again, two different correlation length exponents,
and , are obtained in different channels. We also confirm
the stability of the values of these exponents with respect to the variation of
the distance from the critical point at which they are determined. These
results further demonstrate universal critical behaviour of the model at least
up to correlation lengths of 4 lattice spacings when the phase transition is
approached in some interval at .Comment: 16 page
The effective potential and the renormalisation group
We discuss renormalisation group improvement of the effective potential both
in general and in the context of scalar \p^4 and the Standard Model.
In the latter case we find that absolute stability of the electroweak vacuum
implies that , for \as (M_Z) = 0.11. We point out
that the lower bound on {\it decreases\/} if \as (M_Z) is increased.Comment: 22 pages plus three PostScript figures (appended), Liverpool preprint
LTH 288, University of Michigan preprint UM-TH-92-2
Wilson loop distributions, higher representations and centre dominance in SU(2)
To help understand the centre dominance picture of confinement, we look at
Wilson loop distributions in pure SU(2) lattice gauge theory. A strong coupling
approximation for the distribution is developed to use for comparisons. We
perform a Fourier expansion of the distribution: centre dominance here
corresponds to suppression of odd terms beyond the first. The Fourier terms
correspond to SU(2) representations; hence Casimir scaling behaviour leads to
centre dominance. We examine the positive plaquette model, where only thick
vortices are present. We show that a simple picture of random, non-interacting
centre vortices gives a string tension about 3/4 of the measured value.
Finally, we attempt to limit confusion about the adjoint representation.Comment: 18 pages, 8 figures, LaTeX 2e with epsfig and amstex; discussion
following eq. 24 modified; figure 8 replotted; various references added;
substance unchange
On the Crumpling Transition in Crystalline Random Surfaces
We investigate the crumpling transition on crystalline random surfaces with
extrinsic curvature on lattices up to . Our data are consistent with a
second order phase transition and we find correlation length critical exponent
. The specific heat exponent, , is in
much better agreement with hyperscaling than hitherto. The long distance
behaviour of tangent-tangent correlation functions confirms that the so-called
Hausdorff dimension is throughout the crumpled phase.Comment: 9 pages latex plus 5 postscript figures, OUTP 92/40
- âŠ