O(4) Expansion of the ladder Bethe-Salpeter equation

The Bethe-Salpeter amplitude is expanded on a hyperspherical basis, thereby reducing the original 4-dimensional integral equation into an infinite set of coupled 1-dimensional ones. It is shown that this representation offers a highly accurate method to determine numerically the bound state solutions. For generic cases only a few hyperspherical waves are needed to achieve convergence, both for the ground state as well as for radially or orbitally excited states. The wave function is reconstructed for several cases and in particular it is shown that it becomes independent of the relative time in the nonrelativistic regime.Comment: 21 pages, revte

Relativistic covariance of quasipotential equations

We argue that most of the relativistic 3-D (quasipotential) equations used in hadron physics are inconsistent with the discrete symmetries like charge conjugation and CPT, yielding an incorrect Lorentz structure for the calculated Green's functions. An exception to this is the equal time approximation to the Bethe-Salpeter equation. We present a covariant quasipotential model for the pion-nucleon interaction based on hadronic degrees of freedom and satisfying the full covariance.Comment: 7 pages, LaTeX (REVTeX), incl. 4 PostScript figure

Nuclear Matter Studies with Density-dependent Meson-Nucleon Coupling Constants

Due to the internal structure of the nucleon, we should expect, in general, that the effective meson nucleon parameters may change in nuclear medium. We study such changes by using a chiral confining model of the nucleon. We use density-dependent masses for all mesons except the pion. Within a Dirac-Brueckner analysis, based on the relativistic covariant structure of the NN amplitude, we show that the effect of such a density dependence in the NN interaction on the saturation properties of nuclear matter, while not large, is quite significant. Due to the density dependence of the $g_{\sigma NN}$, as predicted by the chiral confining model, we find, in particular, a looping behavior of the binding energy at saturation as a function of the saturation density. A simple model is described, which exhibits looping and which is shown to be mainly caused by the presence of a peak in the density dependence of the medium modified $\sigma N$ coupling constant at low density. The effect of density dependence of the coupling constants and the meson masses tends to improve the results for $E/A$ and density of nuclear matter at saturation. From the present study we see that the relationship between binding energy and saturation density may not be as universal as found in nonrelativistic studies and that more model dependence is exhibited once medium modifications of the basic nuclear interactions are considered.Comment: Acknowledgements have been modified. 34 pages, revtex, uuencoded gz-compressed tar fil

Global analysis of proton elastic form factor data with two-photon exchange corrections

We use the world's data on elastic electron--proton scattering and calculations of two-photon exchange effects to extract corrected values of the proton's electric and magnetic form factors over the full Q^2 range of the existing data. Our analysis combines the corrected Rosenbluth cross section and polarization transfer data, and is the first extraction of G_Ep and G_Mp including explicit two-photon exchange corrections and their associated uncertainties. In addition, we examine the angular dependence of the corrected cross sections, and discuss the possible nonlinearities of the cross section as a function of epsilon.Comment: 13 pages, 3 figures, 4 tables, to be submitted to Phys. Rev.