1,822 research outputs found
Exploring the Dynamics of Three-Dimensional Lattice Gauge Theories by External Fields
We investigate the dynamics of three-dimensional lattice gauge theories by
means of an external Abelian magnetic field. For the SU(2) lattice gauge theory
we find evidence of the unstable modes.Comment: 3 pages, PostScript. Contribution to the LATTICE 93 Conference
(Dallas, U.S.A., September 1993) preprint BARI-TH-162/9
Perturbative Wilson loops from unquenched Monte Carlo simulations at weak couplings
Perturbative expansions of several small Wilson loops are computed through
next-to-next-to-leading order in unquenched lattice QCD, from Monte Carlo
simulations at weak couplings. This approach provides a much simpler
alternative to conventional diagrammatic perturbation theory, and is applied
here for the first time to full QCD. Two different sets of lattice actions are
considered: one set uses the unimproved plaquette gluon action together with
the unimproved staggered-quark action; the other set uses the one-loop-improved
Symanzik gauge-field action together with the so-called ``asqtad''
improved-staggered quark action. Simulations are also done with different
numbers of dynamical fermions. An extensive study of the systematic
uncertainties is presented, which demonstrates that the small third-order
perturbative component of the observables can be reliably extracted from
simulation data. We also investigate the use of the rational hybrid Monte Carlo
algorithm for unquenched simulations with unimproved-staggered fermions. Our
results are in excellent agreement with diagrammatic perturbation theory, and
provide an important cross-check of the perturbation theory input to a recent
determination of the strong coupling by the HPQCD
collaboration.Comment: 14 pages, 8 figure
Development and validation of clinical profiles of patients hospitalized due to behavioral and psychological symptoms of dementia.
Patients hospitalized on acute psychogeriatric wards are a heterogeneous population. Cluster analysis is a useful statistical method for partitioning a sample of patients into well separated groups of patients who present common characteristics. Several patient profile studies exist, but they are not adapted to acutely hospitalized psychogeriatric patients with cognitive impairment. The present study aims to partition patients hospitalized due to behavioral and psychological symptoms of dementia into profiles based on a global evaluation of mental health using cluster analysis.
Using nine of the 13 items from the Health of the Nation Outcome Scales for elderly people (HoNOS65+), data were collected from a sample of 542 inpatients with dementia who were hospitalized between 2011 and 2014 in acute psychogeriatric wards of a Swiss university hospital. An optimal clustering solution was generated to represent various profiles, by using a mixed approach combining hierarchical and non-hierarchical (k-means) cluster analyses associated with a split-sample cross-validation. The quality of the clustering solution was evaluated based on a cross-validation, on a k-means method with 100 random initial seeds, on validation indexes, and on clinical interpretation.
The final solution consisted of four clinically distinct and homogeneous profiles labeled (1) BPSD-affective, (2) BPSD-functional, (3) BPSD-somatic and (4) BPSD-psychotic according to their predominant clinical features. The four profiles differed in cognitive status, length of hospital stay, and legal admission status.
In the present study, clustering methods allowed us to identify four profiles with distinctive characteristics. This clustering solution may be developed into a classification system that may allow clinicians to differentiate patient needs in order to promptly identify tailored interventions and promote better allocation of available resources
The Savvidy ``ferromagnetic vacuum'' in three-dimensional lattice gauge theory
The vacuum effective potential of three-dimensional SU(2) lattice gauge
theory in an applied color-magnetic field is computed over a wide range of
field strengths. The background field is induced by an external current, as in
continuum field theory. Scaling and finite volume effects are analyzed
systematically. The first evidence from lattice simulations is obtained of the
existence of a nontrivial minimum in the effective potential. This supports a
``ferromagnetic'' picture of gluon condensation, proposed by Savvidy on the
basis of a one-loop calculation in (3+1)-dimensional QCD.Comment: 9pp (REVTEX manuscript). Postscript figures appende
Unstable Modes in Three-Dimensional SU(2) Gauge Theory
We investigate SU(2) gauge theory in a constant chromomagnetic field in three
dimensions both in the continuum and on the lattice. Using a variational method
to stabilize the unstable modes, we evaluate the vacuum energy density in the
one-loop approximation. We compare our theoretical results with the outcomes of
the numerical simulations.Comment: 24 pages, REVTEX 3.0, 3 Postscript figures included. (the whole
postscript file (text+figures) is available on request from
[email protected]
A Non-Abelian Variation on the Savvidy Vacuum of the Yang-Mills Gauge Theory
As a prelude to a truly non-perturbative evaluation of the effective
potential in terms of lattice QCD, the one loop effective potential for a
non-Abelian gauge configuration is calculated using the background field
method. Through a non-trivial correlation between the space and color
orientations the new background field avoids the possible coordinate
singularity, , observed recently by Ken Johnson and his
collaborators in their Schr\"{o}dinger functional study of the SU(2) Yang-Mills
theory. In addition, since our ansatz generates a constant color magnetic field
through the commutator terms rather than derivative terms, many of the
technical drawbacks the Savvidy ansatz suffers on a lattice can be avoided. Our
one loop study yields qualitatively the same result as that of Savvidy's.Comment: 9 pages, preprint BU-HEP-93-2
Numerical Stochastic Perturbation Theory for full QCD
We give a full account of the Numerical Stochastic Perturbation Theory method
for Lattice Gauge Theories. Particular relevance is given to the inclusion of
dynamical fermions, which turns out to be surprisingly cheap in this context.
We analyse the underlying stochastic process and discuss the convergence
properties. We perform some benchmark calculations and - as a byproduct - we
present original results for Wilson loops and the 3-loop critical mass for
Wilson fermions.Comment: 35 pages, 5 figures; syntax revise
Meson Decay Constants from Isospin Mass Splittings in the Quark Model
Decay constants of and mesons are estimated within the framework of a
heavy-quark approach using measured isospin mass splittings in the , ,
and states to isolate the electromagnetic hyperfine interaction between
quarks. The values MeV and MeV are
obtained. Only experimental errors are given; possible theoretical ambiguities,
and suggestions for reducing them, are noted.Comment: 7 pages, LaTeX, EFI-92-3
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