26,036 research outputs found
Comparison of Nucleon Form Factors from Lattice QCD Against the Light Front Cloudy Bag Model and Extrapolation to the Physical Mass Regime
We explore the possibility of extrapolating state of the art lattice QCD
calculations of nucleon form factors to the physical regime. We find that the
lattice results can be reproduced using the Light Front Cloudy Bag Model by
letting its parameters be analytic functions of the quark mass. We then use the
model to extend the lattice calculations to large values of Q^{2} of interest
to current and planned experiments. These functions are also used to define
extrapolations to the physical value of the pion mass, thereby allowing us to
study how the predicted zero in G_{E}(Q^{2})/G_{M}(Q^{2}) varies as a function
of quark mass.Comment: 31 pages, 22 figure
Electromagnetic Gauge Invariance of the Cloudy Bag Model
We examine the question of the gauge invariance of electromagnetic form
factors calculated within the cloudy bag model. One of the assumptions of the
model is that electromagnetic form factors are most accurately evaluated in the
Breit frame. This feature is used to show that gauge invariance is respected in
this frame.Comment: 8 pages, RevTex, 1 figure, to be published in Phys. Rev.
The Radius of the Proton: Size Does Matter
The measurement by Pohl et al. [1] of the 2S_1/2^F=1 to 2P_3/2^F=2 transition
in muonic hydrogen and the subsequent analysis has led to a conclusion that the
rms charge radius of the proton differs from the accepted (CODATA [2]) value by
approximately 4%, leading to a 4.9 s.d. discrepancy. We investigate the muonic
hydrogen spectrum relevant to this transition using bound-state QED with Dirac
wave-functions and comment on the extent to which the perturbation-theory
analysis which leads to the above conclusion can be confirmed.Comment: Delayed arXiv submission. To appear in 'Proceedings of T(R)OPICALQCD
2010' (September 26 - October 1, 2010). 7 pages, 1 figure. Superseded by
arXiv:1104.297
Embedded density functional theory for covalently bonded and strongly interacting subsystems
Embedded density functional theory (e-DFT) is used to describe the electronic structure of strongly interacting molecular subsystems. We present a general implementation of the Exact Embedding (EE) method [J. Chem. Phys. 133, 084103 (2010)] to calculate the large contributions of the nonadditive kinetic potential (NAKP) in such applications. Potential energy curves are computed for the dissociation of Li^+–Be, CH_3–CF_3, and hydrogen-bonded water clusters, and e-DFT results obtained using the EE method are compared with those obtained using approximate kinetic energy functionals. In all cases, the EE method preserves excellent agreement with reference Kohn–Sham calculations, whereas the approximate functionals lead to qualitative failures in the calculated energies and equilibrium structures. We also demonstrate an accurate pairwise approximation to the NAKP that allows for efficient parallelization of the EE method in large systems; benchmark calculations on molecular crystals reveal ideal, size-independent scaling of wall-clock time with increasing system size
The Changing Financial Structure of the U.S. Farm Sector
Agricultural Finance,
Study of Lattice QCD Form Factors Using the Extended Gari-Krumpelmann Model
We explore the suitability of a modern vector meson dominance (VMD) model as
a method for chiral extrapolation of nucleon electromagnetic form factor
simulations in lattice QCD. It is found that the VMD fits to experimental data
can be readily generalized to describe the lattice simulations. However, the
converse is not true. That is, the VMD form is unsuitable as a method of
extrapolation of lattice simulations at large quark mass to the physical
regime.Comment: 14 pages, 5 figure
Taming the Pion Cloud of the Nucleon
We present a light-front determination of the pionic contribution to the
nucleon self-energy, , to second-order in pion-baryon coupling
constants that allows the pion-nucleon vertex function to be treated in a
model-independent manner constrained by experiment. The pion mass
dependence of is consistent with chiral perturbation theory
results for small values of and is also linearly dependent on for
larger values, in accord with the results of lattice QCD calculations. The
derivative of with respect to yields the dominant
contribution to the pion content, which is consistent with the
difference observed experimentally in the violation of the
Gottfried sum rule.Comment: 11 pages, 3 figure
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