803 research outputs found
Monopole Percolation and The Universality Class of the Chiral Transition in Four Flavor Noncompact Lattice QED
We simulate four flavor noncompact lattice QED using the Hybrid Monte Carlo
algorithm on and lattices. Measurements of the monopole
susceptibility and the percolation order parameter indicate a transition at
with critical behavior in the universality class of
four dimensional percolation. We present accurate chiral condensate
measurements and monitor finite size effects carefully. The chiral condensate
data supports the existence of a power-law transition at in the
same universality class as the chiral transition in the two flavor model. The
resulting equation of state predicts the mass ratio in
good agreement with spectrum calculations while the hypothesis of a
logarithmically improved mean field theory fails qualitatively.Comment: 17 pages, 10 figure
Large N Lattice QED
We study the critical behaviour of non compact QED with
species of light fermions, using a method we have proposed for unquenched
simulations. We find that there exist two phase transition lines: one, second
order, and the other, first order, that approaches asymptotically the
axis. These two lines have different physical origin, the second one being
entirely due to fermions effects. We discuss the effect of the approximation
used, in terms of an expansion of the effective action in powers of , and
conclude that the general features should not be affected by this
approximation.Comment: 9 pages. LNF 92/110
The Continuum Limit of Non Compact QED
Since four-fermion operators in strongly coupled are nonperturbatively
renormalizable, we analyze here the phase diagram and critical behaviour of the
Gauged Nambu-Jona Lasinio model. Our mean field approximation relates the
critical exponents along the continuous phase transition line with the mass
dependence of the chiral condensate in the Coulomb phase of standard noncompact
. The numerical results for noncompact strongly suggest non mean
field exponents along the critical line.Comment: Presented at Lattice '95. Figures on reques
Four - Fermi Theories in Fewer Than Four Dimensions
Four-fermi models in dimensionality exhibit an ultra-violet stable
renormalization group fixed point at a strong value of the coupling constant
where chiral symmetry is spontaneously broken. The resulting field theory
describes relativistic fermions interacting non-trivially via exchange of
scalar bound states. We calculate the corrections to this picture,
where is the number of fermion species, for a variety of models and
confirm their renormalizability to this order. A connection between
renormalizability and the hyperscaling relations between the theory's critical
exponents is made explicit. We present results of extensive numerical
simulations of the simplest model for , performed using the hybrid Monte
Carlo algorithm on lattice sizes ranging from to . For
species of massless fermions we confirm the existence of a second order phase
transition where chiral symmetry is spontaneously broken. Using both direct
measurement and finite size scaling arguments we estimate the critical
exponents , , and . We also investigate symmetry
restoration at non-zero temperature, and the scalar two-point correlation
function in the vicinity of the bulk transition. All our results are in
excellent agreement with analytic predictions, and support the contention that
the expansion is accurate for this class of models.Comment: CERN-TH.6557/92 ILL-(TH)-92-\# 19, 60 pages, 18 figures (not
included
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