12,766 research outputs found
Progress using generalized lattice Dirac operators to parametrize the Fixed-Point QCD action
We report on an ongoing project to parametrize the Fixed-Point Dirac operator
for massless quarks, using a very general construction which has arbitrarily
many fermion offsets and gauge paths, the complete Clifford algebra and
satisfies all required symmetries. Optimizing a specific construction with
hypercubic fermion offsets, we present some preliminary results.Comment: Lattice 2000 (Improvement), 9 pages, based on a talk by K.H. and a
poster by T.J. References adde
The construction of generalized Dirac operators on the lattice
We discuss the steps to construct Dirac operators which have arbitrary
fermion offsets, gauge paths, a general structure in Dirac space and satisfy
the basic symmetries (gauge symmetry, hermiticity condition, charge
conjugation, hypercubic rotations and reflections) on the lattice. We give an
extensive set of examples and offer help to add further structures.Comment: 19 pages, latex, maple code attache
AlkoxyalleneâBased LANCA ThreeâComponent Synthesis of 1,2âDiketones, Quinoxalines, and Unique Isoindenone Dimers and a Computational Study of the Isoindenone Dimerization
A series of ÎČâalkoxyâÎČâketoenamides was prepared by the wellâestablished LANCA threeâcomponent reaction of lithiated 1â(2âtrimethylsilylethoxy)âsubstituted allenes, nitriles, and α,ÎČâunsaturated carboxylic acids. The αâtertâbutylâsubstituted compounds were smoothly converted into the expected 1,2âdiketones by treatment with trifluoroacetic acid. A subsequent condensation of the 1,2âdiketones with oâphenylenediamine provided the desired highly substituted quinoxalines in good overall yield. Surprisingly, the αâphenylâsubstituted ÎČâalkoxyâÎČâketoenamides investigated afford not only the expected 1,2âdiketones, but also pentacyclic compounds with an antiâtricyclo[4.2.1.12,5]decaâ3,7âdieneâ9,10âdione core. These interesting products are very likely the result of an isoindenone dimerization which was mechanistically studied with the support of DFT calculations. Under the strongly acidic reaction conditions, a stepwise reaction is likely leading to a protonated isoindenone as reactive intermediate. It may first form a van der Waals complex with a neutral isoindenone before the two regioâ and diastereoselective ring forming steps occur. Interestingly, two neutral or two protonated isoindenones are also predicted to dimerize giving the observed pentacyclic product
Another weak first order deconfinement transition: three-dimensional SU(5) gauge theory
We examine the finite-temperature deconfinement phase transition of
(2+1)-dimensional SU(5) Yang-Mills theory via non-perturbative lattice
simulations. Unsurprisingly, we find that the transition is of first order,
however it appears to be weak. This fits naturally into the general picture of
"large" gauge groups having a first order deconfinement transition, even when
the center symmetry associated with the transition might suggest otherwise.Comment: 17 pages, 8 figure
Adaptive intelligence applied to numerical optimisation
The article presents modification strategies theoretical comparison and experimental results achieved by adaptive heuristics applied to numerical optimisation of several non-constraint test functions. The aims of the study are to identify and compare how adaptive search heuristics behave within heterogeneous search space without retuning of the search parameters. The achieved results are summarised and analysed, which could be used for comparison to other methods and further investigation
Absence of evidence for pentaquarks on the lattice
We study the question of whether or not QCD predicts a pentaquark state. We
use the improved, fixed point lattice QCD action which has very little
sensitivity to the lattice spacing and also allows us to reach light quark
masses. The analysis was performed on a single volume of size with lattice spacing of fm. We use the
correlation matrix method to identify the ground and excited states in the
isospin 0, negative parity channel. In the quenched approximation where
dynamical quark effects are omitted, we do not find any evidence for a
pentaquark resonance in QCD.Comment: 17 pages, 5 figures replaced with revised versio
Electronic structure theory of the hidden order material URuSi
We report a comprehensive electronic structure investigation of the
paramagnetic (PM), the large moment antiferromagnetic (LMAF), and the hidden
order (HO) phases of URuSi. We have performed relativistic
full-potential calculations on the basis of the density functional theory
(DFT), employing different exchange-correlation functionals to treat electron
correlations within the open -shell of uranium. Specifically, we
investigate---through a comparison between calculated and low-temperature
experimental properties---whether the electrons are localized or
delocalized in URuSi. We also performed dynamical mean field theory
calculations (LDA+DMFT) to investigate the temperature evolution of the
quasi-particle states at 100~K and above, unveiling a progressive opening of a
quasi-particle gap at the chemical potential when temperature is reduced. A
detailed comparison of calculated properties with known experimental data
demonstrates that the LSDA and GGA approaches, in which the uranium
electrons are treated as itinerant, provide an excellent explanation of the
available low-temperature experimental data of the PM and LMAF phases. We show
furthermore that due to a materials-specific Fermi surface instability a large,
but partial, Fermi surface gapping of up to 750 K occurs upon antiferromagnetic
symmetry breaking. The occurrence of the HO phase is explained through
dynamical symmetry breaking induced by a mode of long-lived antiferromagnetic
spin-fluctuations. This dynamical symmetry breaking model explains why the
Fermi surface gapping in the HO phase is similar but smaller than that in the
LMAF phase and it also explains why the HO and LMAF phases have the same Fermi
surfaces yet different order parameters. Suitable derived order parameters for
the HO are proposed to be the Fermi surface gap or the dynamic spin-spin
correlation function.Comment: 23 pages, 20 figure
Relativistic quantum mechanics and the Bohmian interpretation
Conventional relativistic quantum mechanics, based on the Klein-Gordon
equation, does not possess a natural probabilistic interpretation in
configuration space. The Bohmian interpretation, in which probabilities play a
secondary role, provides a viable interpretation of relativistic quantum
mechanics. We formulate the Bohmian interpretation of many-particle wave
functions in a Lorentz-covariant way. In contrast with the nonrelativistic
case, the relativistic Bohmian interpretation may lead to measurable
predictions on particle positions even when the conventional interpretation
does not lead to such predictions.Comment: 10 pages, revised, to appear in Found. Phys. Let
A New Metaheuristic Bat-Inspired Algorithm
Metaheuristic algorithms such as particle swarm optimization, firefly
algorithm and harmony search are now becoming powerful methods for solving many
tough optimization problems. In this paper, we propose a new metaheuristic
method, the Bat Algorithm, based on the echolocation behaviour of bats. We also
intend to combine the advantages of existing algorithms into the new bat
algorithm. After a detailed formulation and explanation of its implementation,
we will then compare the proposed algorithm with other existing algorithms,
including genetic algorithms and particle swarm optimization. Simulations show
that the proposed algorithm seems much superior to other algorithms, and
further studies are also discussed.Comment: 10 pages, 2 figure
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