468 research outputs found
A strong-coupling analysis of two-dimensional O(N) sigma models with on square, triangular and honeycomb lattices
Recently-generated long strong-coupling series for the two-point Green's
functions of asymptotically free lattice models are
analyzed, focusing on the evaluation of dimensionless renormalization-group
invariant ratios of physical quantities and applying resummation techniques to
series in the inverse temperature and in the energy . Square,
triangular, and honeycomb lattices are considered, as a test of universality
and in order to estimate systematic errors. Large- solutions are carefully
studied in order to establish benchmarks for series coefficients and
resummations. Scaling and universality are verified. All invariant ratios
related to the large-distance properties of the two-point functions vary
monotonically with , departing from their large- values only by a few per
mille even down to .Comment: 53 pages (incl. 5 figures), tar/gzip/uuencode, REVTEX + psfi
Eliminating leading corrections to scaling in the 3-dimensional O(N)-symmetric phi^4 model: N=3 and 4
We study corrections to scaling in the O(3)- and O(4)-symmetric phi^4 model
on the three-dimensional simple cubic lattice with nearest neighbour
interactions. For this purpose, we use Monte Carlo simulations in connection
with a finite size scaling method. We find that there exists a finite value of
the coupling lambda^*, for both values of N, where leading corrections to
scaling vanish. As a first application, we compute the critical exponents
nu=0.710(2) and eta=0.0380(10) for N=3 and nu=0.749(2) and eta=0.0365(10) for
N=4.Comment: 21 pages, 2 figure
Topological Density and Instantons on a Lattice
We present an update on the study of topological structure of QCD. Issues
addressed include a comparison between the plaquette and the geometric methods
of calculating the topological density. We show that the improved gauge action
based on sqrt(3) blocking transformation suppresses the formation of
topologically charged dislocations with low action. Using a cooling method we
identify the instantons' location, estimate their size and density, and
calculate the renormalization constant Z_Q for the plaquette method.Comment: 3 Pages, submitted to Proceedings of XII International Symposium on
Lattice Field Theory (Lattice 94, Bielefeld). uuencoded tar file includes
figures as TeXDraw (.tex) file
Renormalization and topological susceptibility on the lattice: SU(2) Yang-Mills theory
The renormalization functions involved in the determination of the
topological susceptibility in the SU(2) lattice gauge theory are extracted by
direct measurements, without relying on perturbation theory. The determination
exploits the phenomenon of critical slowing down to allow the separation of
perturbative and non-perturbative effects. The results are in good agreement
with perturbative computations.Comment: 12 pages + 4 figures (PostScript); report no. IFUP-TH 10/9
Entanglement and particle correlations of Fermi gases in harmonic traps
We investigate quantum correlations in the ground state of noninteracting
Fermi gases of N particles trapped by an external space-dependent harmonic
potential, in any dimension. For this purpose, we compute one-particle
correlations, particle fluctuations and bipartite entanglement entropies of
extended space regions, and study their large-N scaling behaviors. The
half-space von Neumann entanglement entropy is computed for any dimension,
obtaining S_HS = c_l N^(d-1)/d ln N, analogously to homogenous systems, with
c_l=1/6, 1/(6\sqrt{2}), 1/(6\sqrt{6}) in one, two and three dimensions
respectively. We show that the asymptotic large-N relation S_A\approx \pi^2
V_A/3, between the von Neumann entanglement entropy S_A and particle variance
V_A of an extended space region A, holds for any subsystem A and in any
dimension, analogously to homogeneous noninteracting Fermi gases.Comment: 15 pages, 22 fig
Topology in 2D CP**(N-1) models on the lattice: a critical comparison of different cooling techniques
Two-dimensional CP**(N-1) models are used to compare the behavior of
different cooling techniques on the lattice. Cooling is one of the most
frequently used tools to study on the lattice the topological properties of the
vacuum of a field theory. We show that different cooling methods behave in an
equivalent way. To see this we apply the cooling methods on classical
instantonic configurations and on configurations of the thermal equilibrium
ensemble. We also calculate the topological susceptibility by using the cooling
technique.Comment: 24 pages, 10 figures (from 16 eps files
Large-N phase transition in lattice 2-d principal chiral models
We investigate the large-N critical behavior of 2-d lattice chiral models by
Monte Carlo simulations of U(N) and SU(N) groups at large N. Numerical results
confirm strong coupling analyses, i.e. the existence of a large-N second order
phase transition at a finite .Comment: 12 pages, Revtex, 8 uuencoded postscript figure
Geometric Measurement of Topological Susceptibility on Large Lattices
The topological susceptibility of the quenched QCD vacuum is measured on
large lattices for three values from to . Charges possibly
induced by dislocations are identified and shown to have little effect
on the measured susceptibility. As increases, fewer such questionable
charges are found. Scaling is checked by examining the ratios of the
susceptibility to previously existing values of the rho mass, string tension,
F-pi, and lambda-lattice.Comment: LaTeX article, 3 pages, uuencoded compressed tar file, 2 figures
included as tex files using axismacros, DVIPS driver required to show
figures. Talk presented by Jeffrey Grandy at Lattice 93, Dallas, Texas. Los
Alamos Preprint number pendin
Gauged O(n) spin models in one dimension
We consider a gauged O(n) spin model, n >= 2, in one dimension which contains
both the pure O(n) and RP(n-1) models and which interpolates between them. We
show that this model is equivalent to the non-interacting sum of the O(n) and
Ising models. We derive the mass spectrum that scales in the continuum limit,
and demonstrate that there are two universality classes, one of which contains
the O(n) and RP(n-1) models and the other which has a tuneable parameter but
which is degenerate in the sense that it arises from the direct sum of the O(n)
and Ising models.Comment: 9 pages, no figures, LaTeX sourc
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