659 research outputs found
Series expansions without diagrams
We discuss the use of recursive enumeration schemes to obtain low and high
temperature series expansions for discrete statistical systems. Using linear
combinations of generalized helical lattices, the method is competitive with
diagramatic approaches and is easily generalizable. We illustrate the approach
using the Ising model and generate low temperature series in up to five
dimensions and high temperature series in three dimensions. The method is
general and can be applied to any discrete model. We describe how it would work
for Potts models.Comment: 24 pages, IASSNS-HEP-93/1
Large Nc Continuum Reduction and the Thermodynamics of QCD
It is noted that if large Nc continuum reduction applies to an observable,
then that observable is independent of temperature for all temperatures below
some critical value. This fact, plus the fact that mesons and glueballs are
weakly interacting at large Nc is used as the basis for a derivation of large
Nc continuum reduction for the chiral condensate. The structure of this
derivation is quite general and can be extended to a wide class of observables
Thermostatistics of extensive and non-extensive systems using generalized entropies
We describe in detail two numerical simulation methods valid to study systems
whose thermostatistics is described by generalized entropies, such as Tsallis.
The methods are useful for applications to non-trivial interacting systems with
a large number of degrees of freedom, and both short-range and long-range
interactions. The first method is quite general and it is based on the
numerical evaluation of the density of states with a given energy. The second
method is more specific for Tsallis thermostatistics and it is based on a
standard Monte Carlo Metropolis algorithm along with a numerical integration
procedure. We show here that both methods are robust and efficient. We present
results of the application of the methods to the one-dimensional Ising model
both in a short-range case and in a long-range (non-extensive) case. We show
that the thermodynamic potentials for different values of the system size N and
different values of the non-extensivity parameter q can be described by scaling
relations which are an extension of the ones holding for the Boltzmann-Gibbs
statistics (q=1). Finally, we discuss the differences in using standard or
non-standard mean value definitions in the Tsallis thermostatistics formalism
and present a microcanonical ensemble calculation approach of the averages.Comment: Submitted to Physica A. LaTeX format, 38 pages, 17 EPS figures.
IMEDEA-UIB, 07071 Palma de Mallorca, Spain, http://www.imedea.uib.e
Numerical Determination of the Distribution of Energies for the XY-model
We compute numerically the distribution of energies W(E,N) for the XY-model
with short-range and long-range interactions. We find that in both cases the
distribution can be fitted to the functional form: W(E,N) ~ exp(N f(E,N)), with
f(E,N) an intensive function of the energy.Comment: 4 pages, 1 figure. Submitted to Physica
Numerical results from large N reduced QCD_2
Some results in QCD_2 at large N are presented using the reduced model on the
lattice. Overlap fermions are used to compute meson propagators.Comment: 3 pages, contribution to Lattice 2002, Bosto
New Algorithm of the Finite Lattice Method for the High-temperature Expansion of the Ising Model in Three Dimensions
We propose a new algorithm of the finite lattice method to generate the
high-temperature series for the Ising model in three dimensions. It enables us
to extend the series for the free energy of the simple cubic lattice from the
previous series of 26th order to 46th order in the inverse temperature. The
obtained series give the estimate of the critical exponent for the specific
heat in high precision.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Letter
Breakdown of large-N quenched reduction in SU(N) lattice gauge theories
We study the validity of the large-N equivalence between four-dimensional
SU(N) lattice gauge theory and its momentum quenched version--the Quenched
Eguchi-Kawai (QEK) model. We find that the assumptions needed for the proofs of
equivalence do not automatically follow from the quenching prescription. We use
weak-coupling arguments to show that large-N equivalence is in fact likely to
break down in the QEK model, and that this is due to dynamically generated
correlations between different Euclidean components of the gauge fields. We
then use Monte-Carlo simulations at intermediate couplings with 20 <= N <= 200
to provide strong evidence for the presence of these correlations and for the
consequent breakdown of reduction. This evidence includes a large discrepancy
between the transition coupling of the "bulk" transition in lattice gauge
theories and the coupling at which the QEK model goes through a strongly
first-order transition. To accurately measure this discrepancy we adapt the
recently introduced Wang-Landau algorithm to gauge theories.Comment: 51 pages, 16 figures, Published verion. Historical inaccuracies in
the review of the quenched Eguchi-Kawai model are corrected, discussion on
reduction at strong-coupling added, references updated, typos corrected. No
changes to results or conclusion
The Effects of Spinal Mobilizations, Manual Stretching, and Exercises in the Treatment of Testicular Pain: A Case Report
The purpose of this case report was to describe the PT management in relieving testicular pain related to genitofemoral nerve entrapment
Phases of three dimensional large N QCD on a continuum torus
It is established by numerical means that continuum large N QCD defined on a
three dimensional torus can exist in four different phases. They are (i)
confined phase; (ii) deconfined phase; (iii) small box at zero temperature and
(iv) small box at high temperatures.Comment: 11 pages, 6 figures, 1 tabl
Modular Invariance, Finiteness, and Misaligned Supersymmetry: New Constraints on the Numbers of Physical String States
We investigate the generic distribution of bosonic and fermionic states at
all mass levels in non-supersymmetric string theories, and find that a hidden
``misaligned supersymmetry'' must always appear in the string spectrum. We show
that this misaligned supersymmetry is ultimately responsible for the finiteness
of string amplitudes in the absence of full spacetime supersymmetry, and
therefore the existence of misaligned supersymmetry provides a natural
constraint on the degree to which spacetime supersymmetry can be broken in
string theory without destroying the finiteness of string amplitudes.
Misaligned supersymmetry also explains how the requirements of modular
invariance and absence of physical tachyons generically affect the distribution
of states throughout the string spectrum, and implicitly furnishes a
two-variable generalization of some well-known results in the theory of modular
functions.Comment: standard LaTeX; 55 pages, 4 figures. (Note: This replaced version
matches the version which was published in Nuclear Physics B.
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