Search results for "electrodynamics"
showing 10 items of 820 documents
Extended Thomas - Fermi expansion from nuclear linear response
1996
The coefficients of the successive orders of the extended Thomas - Fermi expansion of the kinetic energy density are obtained to the leading order in the density inhomogeneities. This is done by comparing the corresponding static polarizability with the exact value in two cases: a non-interacting nuclear infinite system and symmetric nuclear matter with a Skyrme interaction.
Threshold electro production of neutral pions at low q2 off the proton and off the deuteron
2000
Abstract The A1 Collaboration performs an extend program to measure threshold production of the neutral pion as test of Heavy Baryon Chiral Perturbation Theory. Starting with direct threshold measurements to extract the s wave amplitudes at threshold we continued with out of plane measurements with polarized beam to access the small p wave amplitudes. Coherent production off the deuteron is the first attempt to access the neutron amplitude in electro production.
Proton spin and the cheshire cat principle
1991
Abstract We discuss the proton matrix element of the flavor-singlet axial current (FSAC), often referred to as proton spin, in terms of the chiral bag model with due account of the axial anomaly and quantum number fractionation. We conclude that the contribution due to gluons is significant for large bag radii and that it is crucial in order to establish the Cheshire cat principle.
Polarized structure functions of the nucleon in the resonance region
2000
Abstract We present predictions for the spin structure functions of the proton in the framework of a unitary isobar model for one-pion photo- and electroproduction. Our results are compared with recent experimental data from SLAC. The first moments of the calculated structure functions fullfil the Gerasimov-Drell-Hearn and Burkhardt-Cottingham sum rules within an error of typically 5–10%.
Vacuum polarization around stars: Nonlocal approximation
2004
We compute the vacuum polarization associated with quantum massless fields around stars with spherical symmetry. The nonlocal contribution to the vacuum polarization is dominant in the weak field limit, and induces quantum corrections to the exterior metric that depend on the inner structure of the star. It also violates the null energy conditions. We argue that similar results also hold in the low energy limit of quantum gravity. Previous calculations of the vacuum polarization in spherically symmetric spacetimes, based on local approximations, are not adequate for newtonian stars.
Skyrme-force parametrization: Least-squares fit to nuclear ground-state properties.
1986
We investigate systematically the possibilities and the limits of the Skyrme force for reproducing nuclear ground-state properties in a spherical Hartree-Fock calculation. This investigation is performed by means of least-squares fits of the force parameters to the measured binding energy, diffraction radius, and surface width of eight selected nuclei. Particular emphasis is put on the density dependence of the interaction, which turns out to be determined mainly by the surface width. The least-squares fitting procedure yields the best-fit parameters together with uncertainties on them, and it also allows one to estimate the uncertainties of an extrapolation to other fields, e.g., nuclear m…
Three-nucleon calculations with local potentials
1973
The integral equations approach to the three-nucleon problem is reviewed. The results of different calculations with local potentials are compared.
On the variational approach to Jastrow correlations in nuclei
1973
The variational equation determining the Jastrow correlation function is investigated with particular emphasis on the healing problem for both nuclear matter and finite nuclei. The consequences of several healing conditions are discussed. Furthermore, influences from the choice of the single particle basis and from long range correlations are studied and are found to be small in the short range region.
On the effect of excited states in lattice calculations of the nucleon axial charge
2017
Excited-state contamination is one of the dominant uncertainties in lattice calculations of the nucleon axial-charge, $g_A$. Recently published results in leading-order chiral perturbation theory (ChPT) predict the excited-state contamination to be independent of the nucleon interpolator and positive. However, empirical results from numerical lattice calculations show negative contamination (downward curvature), indicating that present-day calculations are not in the regime where the leading-order ChPT predictions apply. In this paper we show that, under plausible assumptions, one can reproduce the behavior of lattice correlators by taking into account final-state $N \pi$ interactions, in p…
Model building by coset space dimensional reduction in ten dimensions with direct product gauge symmetry
2009
14 pages.-- ISI article identifier:000264762400083.-- ArXiv pre-print avaible at:http://arxiv.org/abs/0812.0910