1,066 research outputs found
Two-particle wave function in four dimensional Ising model
An exploratory study of two-particle wave function is carried out with a four
dimensional simple model. The wave functions not only for two-particle ground
and first excited states but also for an unstable state are calculated from
three- and four-point functions using the diagonalization method suggested by
L\"uscher and Wolff. The scattering phase shift is evaluated from these wave
functions.Comment: Poster presented at Lattice2004(spectrum), Fermilab, June 21-26, 200
Perturbative versus Non-perturbative QFT -- Lessons from the O(3) NLS Model
The two-point functions of the energy-momentum tensor and the Noether current
are used to probe the O(3) nonlinear sigma model in an energy range below 10^4
in units of the mass gap . We argue that the form factor approach, with the
form factor series trunctated at the 6-particle level, provides an almost exact
solution of the model in this energy range. The onset of the (2-loop)
perturbative regime is found to occur only at energies around .Comment: 13 pages LaTex, 4 PostScript figures; version published in Physics
Letters
Polynomial Form Factors in the O(3) Nonlinear sigma-Model
We study the general structure of Smirnov's axioms on form factors of local
operators in integrable models. We find various consistency conditions that the
form factor functions have to satisfy. For the special case of the
-model we construct simple polynomial solutions for the operators of
the spin-field, current, energy-momentum tensor and topological charge density.Comment: 11 pages, plain LaTeX, KFKI-1994-10/
PACS photometer calibration block analysis
The absolute stability of the PACS bolometer response over the entire mission
lifetime without applying any corrections is about 0.5% (standard deviation) or
about 8% peak-to-peak. This fantastic stability allows us to calibrate all
scientific measurements by a fixed and time-independent response file, without
using any information from the PACS internal calibration sources. However, the
analysis of calibration block observations revealed clear correlations of the
internal source signals with the evaporator temperature and a signal drift
during the first half hour after the cooler recycling. These effects are small,
but can be seen in repeated measurements of standard stars. From our analysis
we established corrections for both effects which push the stability of the
PACS bolometer response to about 0.2% (stdev) or 2% in the blue, 3% in the
green and 5% in the red channel (peak-to-peak). After both corrections we still
see a correlation of the signals with PACS FPU temperatures, possibly caused by
parasitic heat influences via the Kevlar wires which connect the bolometers
with the PACS Focal Plane Unit. No aging effect or degradation of the
photometric system during the mission lifetime has been found.Comment: 15 pages, accepted for publication in Experimental Astronom
An ideal toy model for confining, walking and conformal gauge theories: the O(3) sigma model with theta-term
A toy model is proposed for four dimensional non-abelian gauge theories
coupled to a large number of fermionic degrees of freedom. As the number of
flavors is varied the gauge theory may be confining, walking or conformal. The
toy model mimicking this feature is the two dimensional O(3) sigma model with a
theta-term. For all theta the model is asymptotically free. For small theta the
model is confining in the infra red, for theta = pi the model has a non-trivial
infra red fixed point and consequently for theta slightly below pi the coupling
walks. The first step in investigating the notoriously difficult systematic
effects of the gauge theory in the toy model is to establish non-perturbatively
that the theta parameter is actually a relevant coupling. This is done by
showing that there exist quantities that are entirely given by the total
topological charge and are well defined in the continuum limit and are
non-zero, despite the fact that the topological susceptibility is divergent.
More precisely it is established that the differences of connected correlation
functions of the topological charge (the cumulants) are finite and non-zero and
consequently there is only a single divergent parameter in Z(theta) but
otherwise it is finite. This divergent constant can be removed by an
appropriate counter term rendering the theory completely finite even at theta >
0.Comment: 9 pages, 2 figures, minor modification, references adde
Broad expertise retrieval in sparse data environments
Expertise retrieval has been largely unexplored on data other than the W3C collection. At the same time, many intranets of universities and other knowledge-intensive organisations offer examples of relatively small but clean multilingual expertise data, covering broad ranges of expertise areas. We first present two main expertise retrieval tasks, along with a set of baseline approaches based on generative language modeling, aimed at finding expertise relations between topics and people. For our experimental evaluation, we introduce (and release) a new test set based on a crawl of a university site. Using this test set, we conduct two series of experiments. The first is aimed at determining the effectiveness of baseline expertise retrieval methods applied to the new test set. The second is aimed at assessing refined models that exploit characteristic features of the new test set, such as the organizational structure of the university, and the hierarchical structure of the topics in the test set. Expertise retrieval models are shown to be robust with respect to environments smaller than the W3C collection, and current techniques appear to be generalizable to other settings
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