1,415 research outputs found
Calculation of fermion loops for and nucleon scalar and electromagnetic form factors
The exact evaluation of the disconnected diagram contributions to the
flavor-singlet pseudoscalar meson mass, the nucleon sigma term and the nucleon
electromagnetic form factors, is carried out utilizing GPGPU technology with
the NVIDIA CUDA platform. The disconnected loops are also computed using
stochastic methods with several noise reduction techniques. Various dilution
schemes as well as the truncated solver method are studied. We make a
comparison of these stochastic techniques to the exact results and show that
the number of noise vectors depends on the operator insertion in the fermionic
loop.Comment: Version accepted for publication in Comp. Phys. Commun. References
added. 13 pages, 12 figure
Nucleon scalar and tensor charges using lattice QCD simulations at the physical value of the pion mass
We present results on the light, strange and charm nucleon scalar and tensor
charges from lattice QCD, using simulations with flavors of twisted
mass Clover-improved fermions with a physical value of the pion mass. Both
connected and disconnected contributions are included, enabling us to extract
the isoscalar, strange and charm charges for the first time directly at the
physical point. Furthermore, the renormalization is computed non-perturbatively
for both isovector and isoscalar quantities. We investigate excited state
effects by analyzing several sink-source time separations and by employing a
set of methods to probe ground state dominance. Our final results for the
scalar charges are , ,
, and for the tensor charges
, ,
, in the scheme at 2~GeV. The first error is statistical, the second is the
systematic error due to the renormalization and the third the systematic
arising from possible contamination due to the excited states.Comment: 20 pages and 13 figure
Novel applications of Lattice QCD: Parton distribution functions, proton charge radius and neutron electric dipole moment
We briefly discuss the current status of lattice QCD simulations and review
selective results on nucleon observables focusing on recent developments in the
lattice QCD evaluation of the nucleon form factors and radii, parton
distribution functions and their moments, and the neutron electric dipole
moment. Nucleon charges and moments of parton distribution functions are
presented using simulations generated at physical values of the quark masses,
while exploratory studies are performed for the parton distribution functions
and the neutron electric dipole moment at heavier than physical value of the
pion mass.Comment: Plenary talk at XII Quark Confinement, 29 August - 3 September, 2016,
Thessaloniki, Greece, 20 pages, 21 figure
Nucleon Properties in the Perturbative Chiral Quark Model
We apply the perturbative chiral quark model (PCQM) to analyse low-energy
nucleon properties: electromagnetic form factors, meson-nucleon sigma-terms and
pion-nucleon scattering. Baryons are described as bound states of valence
quarks surrounded by a cloud of Goldstone bosons (pi, K, eta) as required by
chiral symmetry. The model is based on the following guide lines: chiral
symmetry constraints, fulfilment of low-energy theorems and proper treatment of
sea-quarks, that is meson cloud contributions. Analytic expressions for nucleon
observables are obtained in terms of fundamental parameters of low-energy
pion-nucleon physics (weak pion decay constant, axial nucleon coupling
constant, strong pion-nucleon form factor) and of only one model parameter
(radius of the nucleonic three-quark core). Our results are in good agreement
with experimental data and results of other theoretical approaches.Comment: 8 pages. Invited talk given at Workshop on the Physics of Excited
Nucleons "NSTAR2001", Mainz, Germany, March 7-10, 200
Recent Progress in Quantum Hadrodynamics
Quantum hadrodynamics (QHD) is a framework for describing the nuclear
many-body problem as a relativistic system of baryons and mesons. Motivation is
given for the utility of such an approach and for the importance of basing it
on a local, Lorentz-invariant lagrangian density. Calculations of nuclear
matter and finite nuclei in both renormalizable and nonrenormalizable,
effective QHD models are discussed. Connections are made between the effective
and renormalizable models, as well as between relativistic mean-field theory
and more sophisticated treatments. Recent work in QHD involving nuclear
structure, electroweak interactions in nuclei, relativistic transport theory,
nuclear matter under extreme conditions, and the evaluation of loop diagrams is
reviewed.Comment: 115 pages, REVTeX 3.0 with epsf.sty, ijmpe1.sty, srev.sty,
symbols.sty, plus 10 figure
A Chiral Effective Lagrangian for Nuclei
An effective hadronic lagrangian consistent with the symmetries of quantum
chromodynamics and intended for applications to finite-density systems is
constructed. The degrees of freedom are (valence) nucleons, pions, and the
low-lying non-Goldstone bosons, which account for the intermediate-range
nucleon-nucleon interactions and conveniently describe the nonvanishing
expectation values of nucleon bilinears. Chiral symmetry is realized
nonlinearly, with a light scalar meson included as a chiral singlet to describe
the mid-range nucleon-nucleon attraction. The low-energy electromagnetic
structure of the nucleon is described within the theory using vector-meson
dominance, so that external form factors are not needed. The effective
lagrangian is expanded in powers of the fields and their derivatives, with the
terms organized using Georgi's ``naive dimensional analysis''. Results are
presented for finite nuclei and nuclear matter at one-baryon-loop order, using
the single-nucleon structure determined within the model. Parameters obtained
from fits to nuclear properties show that naive dimensional analysis is a
useful principle and that a truncation of the effective lagrangian at the first
few powers of the fields and their derivatives is justified.Comment: 43 pages, REVTeX 3.0 with epsf.sty, plus 12 figure
Baryons as non-topological chiral solitons
The present review gives a survey of recent developments and applications of
the Nambu--Jona-Lasinio model with and quark flavors for the
structure of baryons. The model is an effective chiral quark theory which
incorporates the SU(N)SU(N)U(1) approximate
symmetry of Quantum chromodynamics. The approach describes the spontaneous
chiral symmetry breaking and dynamical quark mass generation. Mesons appear as
quark-antiquark excitations and baryons arise as non-topological solitons with
three valence quarks and a polarized Dirac sea. For the evaluation of the
baryon properties the present review concentrates on the non-linear
Nambu--Jona-Lasinio model with quark and Goldstone degrees of freedom which is
identical to the Chiral quark soliton model obtained from the instanton liquid
model of the QCD vacuum. In this non-linear model, a wide variety of
observables of baryons of the octet and decuplet is considered. These include,
in particular, electromagnetic, axial, pseudoscalar and pion nucleon form
factors and the related static properties like magnetic moments, radii and
coupling constants of the nucleon as well as the mass splittings and
electromagnetic form factors of hyperons. Predictions are given for the strange
form factors, the scalar form factor and the tensor charge of the nucleon.Comment: 104 pages, 27 figures as uuencoded and compressed postscript files ,
hardcopy available upon request; Prog.Part.Nucl.Phys. 37 (1996) (in print
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