83 research outputs found
Gauge potential singularities and the gluon condensate at finite temperatures
The continuum limit of SU(2) lattice gauge theory is carefully investigated
at zero and at finite temperatures. It is found that the continuum gauge field
has singularities originating from center degrees of freedom being discovered
in Landau gauge. Our numerical results show that the density of these
singularities properly extrapolates to a non-vanishing continuum limit. The
action density of the non-trivial Z_2 links is tentatively identified with the
gluon condensate. We find for temperatures larger than the deconfinement
temperature that the thermal fluctuations of the embedded Z_2 gauge theory
result in an increase of the gluon condensate with increasing temperature.Comment: 3 pages, 2 figures, talk presented by K. Langfeld at the 19th
International Symposium on Lattice Field Theory (LATTICE2001), Berlin,
19.-24.8.2001, to appear in the proceeding
Strongly coupled lattice gauge theory with dynamical fermion mass generation in three dimensions
We investigate the critical behaviour of a three-dimensional lattice
\chiU\phi_3 model in the chiral limit. The model consists of a staggered
fermion field, a U(1) gauge field (with coupling parameter ) and a
complex scalar field (with hopping parameter ). Two different methods
are used: 1) fits of the chiral condensate and the mass of the neutral
unconfined composite fermion to an equation of state and 2) finite size scaling
investigations of the Lee-Yang zeros of the partition function in the complex
fermion mass plane. For strong gauge coupling () the critical
exponents for the chiral phase transition are determined. We find strong
indications that the chiral phase transition is in one universality class in
this interval: that of the three-dimensional Gross-Neveu model with two
fermions. Thus the continuum limit of the \chiU\phi_3 model defines here a
nonperturbatively renormalizable gauge theory with dynamical mass generation.
At weak gauge coupling and small , we explore a region in which the
mass in the neutral fermion channel is large but the chiral condensate on
finite lattices very small. If it does not vanish in the infinite volume limit,
then a continuum limit with massive unconfined fermion might be possible in
this region, too.Comment: 27 pages, 16 figure
Study of the Asymptotic Freedom of 2D Yukawa Models on the Lattice
We investigate on the lattice the Yukawa models in 2 dimensions with Z(2) and
U(1) symmetries. These models reduce to the usual and chiral Gross-Neveu
models, respectively, when the kinetic and the selfcoupling terms of the scalar
field are turned off. The numerical data and mean field arguments suggest that,
at least for some range of the scalar field hopping parameter, fermion mass is
dynamically generated for arbitrarily weak Yukawa coupling. The models are
asymptotically free in this coupling, like the Gross-Neveu models, even when
the scalar quartic selfcoupling is strong.Comment: LaTeX, 11 pages (including 4 postscript figures); OUTP-93-01P (HLRZ
93-15
Finite Size Analysis of the U(1) Phase Transition using the World-sheet Formulation
We present a high statistics analysis of the pure gauge compact U(1) lattice
theory using the the world-sheet or Lagrangian loop representation. We have
applied a simulation method that deals directly with (gauge invariant) integer
variables on plaquettes. As a result we get a significant amelioration of the
simulation that allows to work with large lattices avoiding the metaestability
problems that appear using the standard Wilson formulation.Comment: 14 pages, 4 figures. REVTEX and eps
Are there Local Minima in the Magnetic Monopole Potential in Compact QED?
We investigate the influence of the granularity of the lattice on the
potential between monopoles. Using the flux definition of monopoles we
introduce their centers of mass and are able to realize continuous shifts of
the monopole positions. We find periodic deviations from the -behavior of
the monopole-antimonopole potential leading to local extrema. We suppose that
these meta-stabilities may influence the order of the phase transition in
compact QED.Comment: 11 pages, 5 figure
Monopole Percolation in pure gauge compact QED
The role of monopoles in quenched compact QED has been studied by measuring
the cluster susceptibility and the order parameter previously
introduced by Hands and Wensley in the study of the percolation transition
observed in non-compact QED. A correlation between these parameters and the
energy (action) at the phase transition has been observed. We conclude that the
order parameter is a sensitive probe for studying the phase
transition of pure gauge compact QED.Comment: LaTeX file + 4 PS figures, 12 pag., Pre-UAB-FT-308 ILL-(TH)-94-1
Matter Fields in the Lagrangian Loop Representation: Scalar QED
We present the extension of the Lagrangian loop gauge invariant
representation in such a way to include matter fields. The partition function
of lattice compact U(1)-Higgs model is expressed as a sum over closed as much
as open surfaces. We have simulated numerically the loop action equivalent to
the Villain form of the action and mapped out the beta-gamma phase diagram of
this model.Comment: 10 pages, LaTe
Phase transition in the Higgs model of scalar dyons
In the present paper we investigate the phase transition
"Coulomb--confinement" in the Higgs model of abelian scalar dyons -- particles
having both, electric and magnetic , charges. It is shown that by dual
symmetry this theory is equivalent to scalar fields with the effective squared
electric charge e^{*2}=e^2+g^2. But the Dirac relation distinguishes the
electric and magnetic charges of dyons. The following phase transition
couplings are obtained in the one--loop approximation:
\alpha_{crit}=e^2_{crit}/4\pi\approx 0.19,
\tilde\alpha_{crit}=g^2_{crit}/4\pi\approx 1.29 and \alpha^*_{crit}\approx
1.48.Comment: 16 pages, 2 figure
Bounds on the mass of the b' quark, revisited
Recent results from the DELPHI collaboration led us to review the present
bounds on the b' quark mass. We use all available experimental data for m_b' >
96 GeV to constrain the b' quark mass as a function of the
Cabibbo-Kobayashi-Maskawa elements in a sequential four generations model. We
find that there is still room for a b' with a mass larger than 96 GeV.Comment: 9 pages and 7 figures. REVTEX
Mean Field Phase Diagram of SU(2)xSU(2) Lattice Higgs-Yukawa Model at Finite Lambda
The phase diagram of an SU(2)_L x SU(2)_R lattice Higgs-Yukawa model with
finite lambda is constructed using mean field theory. The phase diagram bears a
superficial resemblance to that for infinite lambda, however as lambda is
decreased the paramagnetic region shrinks in size. For small lambda the phase
transitions remain second order, and no new first order transitions are seen.Comment: 9 pages, 3 postscript figures, RevTex. To appear in PR
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