545 research outputs found
Large q expansion of the 2D q-states Potts model
We present a recursive method to calculate a large q expansion of the 2d
q-states Potts model free energies based on the Fortuin-Kasteleyn
representation of the model. With this procedure, we compute directly the
ordered phase partition function up to order 10 in 1/sqrt{q}. The energy
cumulants at the transition can be obtained with suitable resummation and come
out large for q less or around 15. As a consequence, expansions of the free
energies around the transition temperature are useless for not large enough
values of q. In particular the pure phase specific heats are predicted to be
much larger, at q < 15, than the values extracted from current finite size
scaling analysis of extrema, whereas they agree very well with recent values
extracted at the transition point.Comment: 31 pages (tex) including 15 figures (Postscript
Critical Behaviour of the 3d Gross-Neveu and Higgs-Yukawa Models
We measure the critical exponents of the three dimensional Gross-Neveu model
with two four-component fermions. The exponents are inferred from the scaling
behaviour of observables on different lattice sizes. We also calculate the
exponents, through a second order epsilon-expansion around 4d, for the three
dimensional Higgs-Yukawa model, which is expected to be in the same
universality class and we find that the exponents agree. We conclude that the
equivalence of the two models remains valid in 3d at fixed small N_f values.Comment: 14 Latex pages 8 PSfigures included at the
end,BI-TP-93/31,AZPH-TH/93-19,SPhT 93/0
Critical Behavior of the Antiferromagnetic Heisenberg Model on a Stacked Triangular Lattice
We estimate, using a large-scale Monte Carlo simulation, the critical
exponents of the antiferromagnetic Heisenberg model on a stacked triangular
lattice. We obtain the following estimates: ,
. These results contradict a perturbative
Renormalization Group calculation that points to Wilson-Fisher O(4) behaviour.
While these results may be coherent with results from
Landau-Ginzburg analysis, they show the existence of an unexpectedly rich
structure of the Renormalization Group flow as a function of the dimensionality
and the number of components of the order parameter.Comment: Latex file, 10 pages, 1 PostScript figure. Was posted with a wrong
Title !
Screening correlators with chiral Fermions
We study screening correlators of quark-antiquark composites at T=2T_c, where
T_c is the QCD phase transition temperature, using overlap quarks in the
quenched approximation of lattice QCD. As the lattice spacing is changed from
1/4T to a=1/6T and 1/8T, we find that screening correlators change little, in
contrast with the situation for other types of lattice fermions. All
correlators are close to the ideal gas prediction at small separations. The
long distance falloff is clearly exponential, showing that a parametrization by
a single screening length is possible at distances z > 1/T. The correlator
corresponding to the thermal vector is close to the ideal gas value at all
distances, whereas that for the thermal scalar deviates at large distances.
This is examined through the screening lengths and momentum space correlators.
There is strong evidence that the screening transfer matrix does not have
reflection positivity.Comment: 10 pages, 9 fig
Quenched QCD at finite temperature with chiral Fermions
We study physics at temperatures just above the QCD phase transition (Tc) using chiral (overlap) Fermions in the quenched approximation of lattice QCD. Exact zero modes of the overlap Dirac operator are localized and their frequency of occurrence drops with temperature. This is closely related to axial U(1) symmetry, which remains broken up to 2Tc. After subtracting the effects of these zero modes, chiral symmetry is restored, as indicated by the behavior of the chiral condensate. The pseudoscalar and vector screening masses are close to ideal gas values
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