50 research outputs found
Systematic errors due to linear congruential random-number generators with the Swendsen-Wang algorithm: A warning
We show that linear congruential pseudo-random-number generators can cause
systematic errors in Monte Carlo simulations using the Swendsen-Wang algorithm,
if the lattice size is a multiple of a very large power of 2 and one random
number is used per bond. These systematic errors arise from correlations within
a single bond-update half-sweep. The errors can be eliminated (or at least
radically reduced) by updating the bonds in a random order or in an aperiodic
manner. It also helps to use a generator of large modulus (e.g. 60 or more
bits).Comment: Revtex4, 4 page
Parametric Representation of Noncommutative Field Theory
In this paper we investigate the Schwinger parametric representation for the
Feynman amplitudes of the recently discovered renormalizable quantum
field theory on the Moyal non commutative space. This
representation involves new {\it hyperbolic} polynomials which are the
non-commutative analogs of the usual "Kirchoff" or "Symanzik" polynomials of
commutative field theory, but contain richer topological information.Comment: 31 pages,10 figure
Spectral noncommutative geometry and quantization: a simple example
We explore the relation between noncommutative geometry, in the spectral
triple formulation, and quantum mechanics. To this aim, we consider a dynamical
theory of a noncommutative geometry defined by a spectral triple, and study its
quantization. In particular, we consider a simple model based on a finite
dimensional spectral triple (A, H, D), which mimics certain aspects of the
spectral formulation of general relativity. We find the physical phase space,
which is the space of the onshell Dirac operators compatible with A and H. We
define a natural symplectic structure over this phase space and construct the
corresponding quantum theory using a covariant canonical quantization approach.
We show that the Connes distance between certain two states over the algebra A
(two ``spacetime points''), which is an arbitrary positive number in the
classical noncommutative geometry, turns out to be discrete in the quantum
theory, and we compute its spectrum. The quantum states of the noncommutative
geometry form a Hilbert space K. D is promoted to an operator *D on the direct
product *H of H and K. The triple (A, *H, *D) can be viewed as the quantization
of the family of the triples (A, H, D).Comment: 7 pages, no figure
The One-loop UV Divergent Structure of U(1) Yang-Mills Theory on Noncommutative R^4
We show that U(1) Yang-Mills theory on noncommutative R^4 can be renormalized
at the one-loop level by multiplicative dimensional renormalization of the
coupling constant and fields of the theory. We compute the beta function of the
theory and conclude that the theory is asymptotically free. We also show that
the Weyl-Moyal matrix defining the deformed product over the space of functions
on R^4 is not renormalized at the one-loop level.Comment: 8 pages. A missing complex "i" is included in the field strength and
the divergent contributions corrected accordingly. As a result the model
turns out to be asymptotically fre
Perturbation theory of the space-time non-commutative real scalar field theories
The perturbative framework of the space-time non-commutative real scalar
field theory is formulated, based on the unitary S-matrix. Unitarity of the
S-matrix is explicitly checked order by order using the Heisenberg picture of
Lagrangian formalism of the second quantized operators, with the emphasis of
the so-called minimal realization of the time-ordering step function and of the
importance of the -time ordering. The Feynman rule is established and is
presented using scalar field theory. It is shown that the divergence
structure of space-time non-commutative theory is the same as the one of
space-space non-commutative theory, while there is no UV-IR mixing problem in
this space-time non-commutative theory.Comment: Latex 26 pages, notations modified, add reference
Dynamic critical behavior of the Swendsen--Wang Algorithm for the three-dimensional Ising model
We have performed a high-precision Monte Carlo study of the dynamic critical
behavior of the Swendsen-Wang algorithm for the three-dimensional Ising model
at the critical point. For the dynamic critical exponents associated to the
integrated autocorrelation times of the "energy-like" observables, we find
z_{int,N} = z_{int,E} = z_{int,E'} = 0.459 +- 0.005 +- 0.025, where the first
error bar represents statistical error (68% confidence interval) and the second
error bar represents possible systematic error due to corrections to scaling
(68% subjective confidence interval). For the "susceptibility-like"
observables, we find z_{int,M^2} = z_{int,S_2} = 0.443 +- 0.005 +- 0.030. For
the dynamic critical exponent associated to the exponential autocorrelation
time, we find z_{exp} \approx 0.481. Our data are consistent with the
Coddington-Baillie conjecture z_{SW} = \beta/\nu \approx 0.5183, especially if
it is interpreted as referring to z_{exp}.Comment: LaTex2e, 39 pages including 5 figure
Noncommutative Field Theories and Smooth Commutative Limits
We consider two model field theories on a noncommutative plane that have
smooth commutative limits. One is the single-component fermion theory with
quartic interaction that vanishes identically in the commutative limit. The
other is a scalar-fermion theory, which extends the scalar field theory with
quartic interaction by adding a fermion. We compute the bound state energies
and the two particle scattering amplitudes exactly.Comment: 8 pages, 2 figure