20,520 research outputs found
Magnetic and axial-vector transitions of the baryon antidecuplet
We report the recent results of the magnetic transitions and axial-vector
transitions of the baryon antidecuplet within the framework of the chiral
quark-soliton model. The dynamical model parameters are fixed by experimental
data for the magnetic moments of the baryon octet, for the hyperon semileptonic
decay constants, and for the singlet axial-vector constant. The transition
magnetic moments and are well reproduced
and other octet-decuplet and octet-antidecuplet transitions are predicted. In
particular, the present calculation of is found to be
below the upper bound that the SELEX collaboration measured very
recently. The results explains consistently the recent findings of a new
resonance from the GRAAL and Tohoku LNS group. We also obtain the transition
axial-vector constants for the from which the decay width of
the pentaquark baryon is determined as a function of the
pion-nucleon sigma term . We investigate the dependence of the
decay width of the on the , with the
varied within the range of the experimental uncertainty. We show that a small
decay width of the , i.e. MeV, is
compatible with the values of all known semileptonic decays with the generally
accepted value of for the proton.Comment: 8 pages, 5 figures, Talk given at the Yukawa International Seminar
(YKIS) 2006, "New frontiers in QCD", Kyoto, Japan, 20 Nov. - 8 Dec. 200
Subtractive renormalization of the NN scattering amplitude at leading order in chiral effective theory
The leading-order nucleon-nucleon (NN) potential derived from chiral
perturbation theory consists of one-pion exchange plus a short-distance contact
interaction. We show that in the 1S0 and 3S1-3D1 channels renormalization of
the Lippmann-Schwinger equation for this potential can be achieved by
performing one subtraction. This subtraction requires as its only input
knowledge of the NN scattering lengths. This procedure leads to a set of
integral equations for the partial-wave NN t-matrix which give
cutoff-independent results for the corresponding NN phase shifts. This
reformulation of the NN scattering equation offers practical advantages,
because only observable quantities appear in the integral equation. The
scattering equation may then be analytically continued to negative energies,
where information on bound-state energies and wave functions can be extracted.Comment: 16 pages, 11 figure
Protein Docking by the Underestimation of Free Energy Funnels in the Space of Encounter Complexes
Similarly to protein folding, the association of two proteins is driven
by a free energy funnel, determined by favorable interactions in some neighborhood of the
native state. We describe a docking method based on stochastic global minimization of
funnel-shaped energy functions in the space of rigid body motions (SE(3)) while accounting
for flexibility of the interface side chains. The method, called semi-definite
programming-based underestimation (SDU), employs a general quadratic function to
underestimate a set of local energy minima and uses the resulting underestimator to bias
further sampling. While SDU effectively minimizes functions with funnel-shaped basins, its
application to docking in the rotational and translational space SE(3) is not
straightforward due to the geometry of that space. We introduce a strategy that uses
separate independent variables for side-chain optimization, center-to-center distance of the
two proteins, and five angular descriptors of the relative orientations of the molecules.
The removal of the center-to-center distance turns out to vastly improve the efficiency of
the search, because the five-dimensional space now exhibits a well-behaved energy surface
suitable for underestimation. This algorithm explores the free energy surface spanned by
encounter complexes that correspond to local free energy minima and shows similarity to the
model of macromolecular association that proceeds through a series of collisions. Results
for standard protein docking benchmarks establish that in this space the free energy
landscape is a funnel in a reasonably broad neighborhood of the native state and that the
SDU strategy can generate docking predictions with less than 5 ďż˝ ligand interface Ca
root-mean-square deviation while achieving an approximately 20-fold efficiency gain compared
to Monte Carlo methods
Magnetic moments of exotic pentaquark baryons
In this talk, we present our recent investigation on the magnetic moments of
the exotic pentaquark states, based on the chiral quark-soliton model, all
relevant intrinsic parameters being fixed by using empirical data.Comment: 5 pages, 1 figure, a talk presented at the 10th International
Conference on Baryons (Baryons04), Palaiseau, October 25-29, 200
Prediction of silicon content in hot metal based on golden sine particle swarm optimization and random forest
Particle Swarm Optimization (PSO) algorithm quickly falls into local optimum, low precision. In this paper, add the golden sine operation to the particle position update. The results show that the improved PSO algorithm has better optimization ability. The main parameters affecting the silicon content in hot metal are selected. Then, calculate the correlation coefficient and significance level between parameters and silicon content in hot metal. Finally, the prediction model of silicon content in hot metal is established based on the Random Forest (RF) optimized by improved PSO. The results show that the hit rate is 87,17 %
Prediction of silicon content in hot metal based on golden sine particle swarm optimization and random forest
Particle Swarm Optimization (PSO) algorithm quickly falls into local optimum, low precision. In this paper, add the golden sine operation to the particle position update. The results show that the improved PSO algorithm has better optimization ability. The main parameters affecting the silicon content in hot metal are selected. Then, calculate the correlation coefficient and significance level between parameters and silicon content in hot metal. Finally, the prediction model of silicon content in hot metal is established based on the Random Forest (RF) optimized by improved PSO. The results show that the hit rate is 87,17 %
Subtractive renormalization of the NN interaction in chiral effective theory up to next-to-next-to-leading order: S waves
We extend our subtractive-renormalization method in order to evaluate the 1S0
and 3S1-3D1 NN scattering phase shifts up to next-to-next-to-leading order
(NNLO) in chiral effective theory. We show that, if energy-dependent contact
terms are employed in the NN potential, the 1S0 phase shift can be obtained by
carrying out two subtractions on the Lippmann-Schwinger equation. These
subtractions use knowledge of the the scattering length and the 1S0 phase shift
at a specific energy to eliminate the low-energy constants in the contact
interaction from the scattering equation. For the J=1 coupled channel, a
similar renormalization can be achieved by three subtractions that employ
knowledge of the 3S1 scattering length, the 3S1 phase shift at a specific
energy and the 3S1-3D1 generalized scattering length. In both channels a
similar method can be applied to a potential with momentum-dependent contact
terms, except that in that case one of the subtractions must be replaced by a
fit to one piece of experimental data.
This method allows the use of arbitrarily high cutoffs in the
Lippmann-Schwinger equation. We examine the NNLO S-wave phase shifts for
cutoffs as large as 5 GeV and show that the presence of linear energy
dependence in the NN potential creates spurious poles in the scattering
amplitude. In consequence the results are in conflict with empirical data over
appreciable portions of the considered cutoff range. We also identify problems
with the use of cutoffs greater than 1 GeV when momentum-dependent contact
interactions are employed. These problems are ameliorated, but not eliminated,
by the use of spectral-function regularization for the two-pion exchange part
of the NN potentialComment: 40 pages, 21 figure
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