181 research outputs found
Nuclear Lattice Simulations with Chiral Effective Field Theory
We study nuclear and neutron matter by combining chiral effective field
theory with non-perturbative lattice methods. In our approach nucleons and
pions are treated as point particles on a lattice. This allows us to probe
larger volumes, lower temperatures, and greater nuclear densities than in
lattice QCD. The low energy interactions of these particles are governed by
chiral effective theory and operator coefficients are determined by fitting to
zero temperature few-body scattering data. Any dependence on the lattice
spacing can be understood from the renormalization group and absorbed by
renormalizing operator coefficients. In this way we have a realistic simulation
of many-body nuclear phenomena with no free parameters, a systematic expansion,
and a clear theoretical connection to QCD. We present results for hot neutron
matter at temperatures 20 to 40 MeV and densities below twice nuclear matter
density.Comment: 41 pages, 23 figure
The Asymptotic Expansion of Lattice Loop Integrals Around the Continuum Limit
We present a method of computing any one-loop integral in lattice
perturbation theory by systematically expanding around its continuum limit. At
any order in the expansion in the lattice spacing, the result can be written as
a sum of continuum loop integrals in analytic regularization and a few genuine
lattice integrals (``master integrals''). These lattice master integrals are
independent of external momenta and masses and can be computed numerically. At
the one-loop level, there are four master integrals in a theory with only
bosonic fields, seven in HQET and sixteen in QED or QCD with Wilson fermions.Comment: 9 pages, 2 figure
Quark condensate in one-flavor QCD
We compute the condensate in QCD with a single quark flavor using numerical
simulations with the overlap formulation of lattice fermions. The condensate is
extracted by fitting the distribution of low lying eigenvalues of the Dirac
operator in sectors of fixed topological charge to the predictions of Random
Matrix Theory. Our results are in excellent agreement with estimates from the
orientifold large-N_c expansion.Comment: 12 pages, 4 figures, REVTeX4, v2: Small changes, extended
introduction, published versio
Currents, Charges, and Canonical Structure of Pseudodual Chiral Models
We discuss the pseudodual chiral model to illustrate a class of
two-dimensional theories which have an infinite number of conservation laws but
allow particle production, at variance with naive expectations. We describe the
symmetries of the pseudodual model, both local and nonlocal, as transmutations
of the symmetries of the usual chiral model. We refine the conventional
algorithm to more efficiently produce the nonlocal symmetries of the model, and
we discuss the complete local current algebra for the pseudodual theory. We
also exhibit the canonical transformation which connects the usual chiral model
to its fully equivalent dual, further distinguishing the pseudodual theory.Comment: 15 pages, ANL-HEP-PR-93-85,Miami-TH-1-93,Revtex (references updated,
format improved to Revtex
Spectrum of the Dirac Operator and Multigrid Algorithm with Dynamical Staggered Fermions
Complete spectra of the staggered Dirac operator \Dirac are determined in
quenched four-dimensional gauge fields, and also in the presence of
dynamical fermions.
Periodic as well as antiperiodic boundary conditions are used.
An attempt is made to relate the performance of multigrid (MG) and conjugate
gradient (CG) algorithms for propagators with the distribution of the
eigenvalues of~\Dirac.
The convergence of the CG algorithm is determined only by the condition
number~ and by the lattice size.
Since~'s do not vary significantly when quarks become dynamic,
CG convergence in unquenched fields can be predicted from quenched
simulations.
On the other hand, MG convergence is not affected by~ but depends on
the spectrum in a more subtle way.Comment: 19 pages, 8 figures, HUB-IEP-94/12 and KL-TH 19/94; comes as a
uuencoded tar-compressed .ps-fil
Critical Phenomena with Linked Cluster Expansions in a Finite Volume
Linked cluster expansions are generalized from an infinite to a finite
volume. They are performed to 20th order in the expansion parameter to approach
the critical region from the symmetric phase. A new criterion is proposed to
distinguish 1st from 2nd order transitions within a finite size scaling
analysis. The criterion applies also to other methods for investigating the
phase structure such as Monte Carlo simulations. Our computational tools are
illustrated at the example of scalar O(N) models with four and six-point
couplings for and in three dimensions. It is shown how to localize
the tricritical line in these models. We indicate some further applications of
our methods to the electroweak transition as well as to models for
superconductivity.Comment: 36 pages, latex2e, 7 eps figures included, uuencoded, gzipped and
tarred tex file hdth9607.te
Treatment with higher dosages of heart failure medication is associated with improved outcome following cardiac resynchronization therapy
Background Cardiac resynchronization therapy (CRT) is associated with improved morbidity and mortality in patients with chronic heart failure (CHF) on optimal medical therapy. The impact of CHF medication optimization following CRT, however, has never been comprehensively evaluated. In the current study, we therefore investigated the effect of CHF medication dosage on morbidity and mortality in CHF patients after CRT implantation. Methods and results Chronic heart failure medication was assessed in 185 patients after CRT implantation. During an overall mean follow-up of 44.6 months, 83 patients experienced a primary endpoint (death, heart transplantation, assist device implantation, or hospitalization for CHF). Treatment with higher dosages of angiotensin-converting enzyme inhibitor (ACE-I) or angiotensin receptor blockers (ARBs) (P = 0.001) and beta-blockers (P < 0.001) as well as with lower dosages of loop diuretics (P < 0.001) was associated with a reduced risk for the primary combined endpoint as well as for all-cause mortality. Echocardiographic super-responders to CRT were treated with higher average dosages of ACE-I/ARBs (68.1 vs. 52.4%, P < 0.01) and beta-blockers (59 vs. 42.2%, P < 0.01). During follow-up, the average dosage of loop diuretics was decreased by 20% in super-responders, but increased by 30% in non-super-responders (P < 0.03). Conclusion The use of higher dosages of neurohormonal blockers and lower dosages of diuretics is associated with reduced morbidity and mortality following CRT implantation. Our data imply a beneficial effect of increasing neurohormonal blockade whenever possible following CRT implantatio
Complex Time Solutions with Nontrivial Topology and Multi Particle Scattering in Yang-Mills Theory
A classical solution to the Yang-Mills theory is given a new semiclassical
interpretation in terms of particle scattering. It solves the complex time
boundary value problem, which arises in the semiclassical approximation to a
multi particle transition probability in the one-instanton sector at fixed
energy. The imaginary part of the action of the solution on the complex time
contour and its topological charge obey the same relation as the self-dual
Euclidean configurations. Hence the solution is relevant for the problem of
tunneling with fermion number violation in the electroweak theory. It describes
transitions from an initial state with a smaller number of particles to a final
state with a larger number of particles. The implications of these results for
multi particle production in the electroweak theory are also discussed.Comment: 10 pgs. (LaTeX), JHU-TIPAC-93001
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