1,152 research outputs found
Chiral-odd generalized parton distributions in constituent quark models
We derive the overlap representation of chiral-odd generalized parton
distributions using the Fock-state decomposition in the transverse-spin basis.
This formalism is applied to the case of light-cone wave functions in a
constituent quark model. Numerical results for the four chiral-odd generalized
parton distributions at the hadronic scale are shown in different kinematics.
In the forward limit we derive the transversity distribution, the tensor charge
and the angular momentum sum rule for quarks with transverse polarization in an
unpolarized nucleon.Comment: 23 pages, 7 figures; one reference added and one formula corrected;
conclusions and discussions unchange
Chiral-Odd Generalized Parton Distributions, Transversity and Double Transverse-Spin Asymmetry in Drell-Yan Dilepton Production
Within the framework of light-cone quantization we derive the overlap
representation of generalized parton distributions for transversely polarized
quarks using the Fock-state decomposition in the transverse-spin basis. We
apply this formalism to the case of light-cone wave functions in a constituent
quark model giving numerical results for the four chiral-odd generalized parton
distributions in a region where they describe the emission and reabsorption of
a quark by the nucleon. With the transversity distribution obtained in the
forward limit of the generalized distribution, we provide some predictions for
the double transverse-spin asymmetry in Drell-Yan dilepton production in the
kinematics of the PAX experiment.Comment: 8 pages, 4 figures. To appear in the Proceedings of the "XI
Conference on Problems in Theoretical Nuclear Physics", Cortona, Italy, 11-14
October 200
Parallel three-dimensional simulations of quasi-static elastoplastic solids
Hypo-elastoplasticity is a flexible framework for modeling the mechanics of
many hard materials under small elastic deformation and large plastic
deformation. Under typical loading rates, most laboratory tests of these
materials happen in the quasi-static limit, but there are few existing
numerical methods tailor-made for this physical regime. In this work, we extend
to three dimensions a recent projection method for simulating quasi-static
hypo-elastoplastic materials. The method is based on a mathematical
correspondence to the incompressible Navier-Stokes equations, where the
projection method of Chorin (1968) is an established numerical technique. We
develop and utilize a three-dimensional parallel geometric multigrid solver
employed to solve a linear system for the quasi-static projection. Our method
is tested through simulation of three-dimensional shear band nucleation and
growth, a precursor to failure in many materials. As an example system, we
employ a physical model of a bulk metallic glass based on the shear
transformation zone theory, but the method can be applied to any
elastoplasticity model. We consider several examples of three-dimensional shear
banding, and examine shear band formation in physically realistic materials
with heterogeneous initial conditions under both simple shear deformation and
boundary conditions inspired by friction welding.Comment: Final version. Accepted for publication in Computer Physics
Communication
Chiral-Odd Generalized Parton Distributions and Transversity in Light-Front Constituent Quark Models
We present the general framework to calculate chiral-odd generalized parton
distributions in the overlap representation using the Fock-state decomposition
in the transverse spin basis. In the forward limit we derive the transversity
distribution, the tensor charge and the angular momentum sum rule for quarks
with transverse polarization in an unpolarized nucleon. Numerical results are
obtained by applying the formalism to the case of light-cone wavefunctions of
constituent quark models.Comment: 8 pages, 3 figures. Invited talk at the "Advanced Studies Institute
on SYMMETRIES AND SPIN" (SPIN-Praha-2006), 19-26 July, 2006, Prague. To be
pubblished in Czechoslovak Journal of Physics. Some references adde
Generalized parton distributions of the nucleon in constituent quark models
Generalized parton distributions (GPDs) are studied at the hadronic
(nonperturbative) scale within different assumptions based on a relativistic
constituent quark model. In particular, by means of a meson-cloud model we
investigate the role of nonperturbative antiquark degrees of freedom and the
valence quark contribution. A QCD evolution of the obtained GPDs is used to add
perturbative effects and to investigate the GPDs' sensitivity to the
nonperturbative ingredients of the calculation at larger (experimental) scale.Comment: 4 pages, 1 figure, presented at the Baryon-04 Conference, Palaiseau
(France), October 25-29, 2004. Nuclear Physics A, to be publishe
A continuous-time analysis of distributed stochastic gradient
We analyze the effect of synchronization on distributed stochastic gradient
algorithms. By exploiting an analogy with dynamical models of biological quorum
sensing -- where synchronization between agents is induced through
communication with a common signal -- we quantify how synchronization can
significantly reduce the magnitude of the noise felt by the individual
distributed agents and by their spatial mean. This noise reduction is in turn
associated with a reduction in the smoothing of the loss function imposed by
the stochastic gradient approximation. Through simulations on model non-convex
objectives, we demonstrate that coupling can stabilize higher noise levels and
improve convergence. We provide a convergence analysis for strongly convex
functions by deriving a bound on the expected deviation of the spatial mean of
the agents from the global minimizer for an algorithm based on quorum sensing,
the same algorithm with momentum, and the Elastic Averaging SGD (EASGD)
algorithm. We discuss extensions to new algorithms which allow each agent to
broadcast its current measure of success and shape the collective computation
accordingly. We supplement our theoretical analysis with numerical experiments
on convolutional neural networks trained on the CIFAR-10 dataset, where we note
a surprising regularizing property of EASGD even when applied to the
non-distributed case. This observation suggests alternative second-order
in-time algorithms for non-distributed optimization that are competitive with
momentum methods.Comment: 9/14/19 : Final version, accepted for publication in Neural
Computation. 4/7/19 : Significant edits: addition of simulations, deep
network results, and revisions throughout. 12/28/18: Initial submissio
On the NN-final-state-interaction in the reaction
The influence of the mutual interaction between the two outgoing nucleons
(NN-FSI) in the reaction has been investigated.
Results for various kinematics are discussed. In general, the effect of
NN-FSI depends on kinematics and the chosen final state in the excitation
spectrum of .Comment: 12 pages Revtex including 4 postscript figure
Nucleon magnetic moments in an extended chiral constituent quark model
We present results for the nucleon magnetic moments in the context of an
extended chiral constituent quark model based on the mechanism of the Goldstone
boson exchange, as suggested by the spontaneous breaking of chiral symmetry in
QCD. The electromagnetic charge-current operator is consistently deduced from
the model Hamiltonian, which includes all force components for the
pseudoscalar, vector and scalar meson exchanges. Thus, the continuity equation
is satisfied for each piece of the interaction, avoiding the introduction of
any further parameter. A good agreement with experimental values is found. The
role of isoscalar two-body operators, not constrained by the continuity
equation, is also investigated.Comment: 7 pages, 1 table, submitted for publication to Phys. Lett. B,
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