Comment on "Nucleon form factors and a nonpointlike diquark"

Authors of Phys. Rev. C 60, 062201 (1999) presented a calculation of the electromagnetic form factors of the nucleon using a diquark ansatz in the relativistic three-quark Faddeev equations. In this Comment it is pointed out that the calculations of these form factors stem from a three-quark bound state current that contains overcounted contributions. The corrected expression for the three-quark bound state current is derived.Comment: 6 pages, 1 figure, revtex, eps

Implementing PCAC in Nonperturbative Models of Pion Production

Traditional few-body descriptions of pion production use integral equations to sum the strong interactions nonperturbatively. Although much physics is thereby included, there has not been a practical way of incorporating the constraints of chiral symmetry into such approaches. Thus the traditional few-body descriptions fail to reflect the underlying theory of strong interactions, QCD, which is largely chirally symmetric. In addition, the lack of chiral symmetry in the few-body approaches means that their predictions of pion production are in principle not consistent with the partial conservation of axial current (PCAC), a fact that has especially large consequences at low energies. We discuss how the recent introduction of the ``gauging of equations method'' can be used to include PCAC into traditional few-body descriptions and thereby solve this long standing problemComment: Contribution to Proceedings, 1st Asia-Pacific Conference on Few-Body Problems in Physics, Noda/Kashiwa, Japan, 23-28 August 1999, to be published by Springer-Verlag as "Few-Body Systems Supplement". 7 pages, revtex, epsf, 3 Postscript figure

In-matter three-body problem

We formulate three-dimensional equations for the finite temperature in-matter three-body problem. Our approach takes into account the full infinite series for the effective pair-interaction kernel, so that all possible two-body sub-processes allowed by the underlying Hamiltonian are retained.Comment: 5 pages, contribution to The 16th National Congress 2005 - Australian Institute of Physic

Few-Body Descriptions of the piNN System in Three and Four Dimensions

We summarise the recent theoretical progress in few-body descriptions of the piNN system. Previous descriptions, both three- and four-dimensional, are shown to possess serious theoretical inconsistencies. We illustrate how three-dimensional approaches suffer from renormalisation problems, and how four-dimensional descriptions contain both overcounting and undercounting of diagrams. We then show how such theoretical problems have been recently overcome, leading to new practical few-body equations for the piNN system.Comment: LaTeX, epsf, 8 pages + 6 figures (appended as uuencoded PS-files), invited talk at Symposium on Meson-Nucleon Physics..., Blaubeuren, Germany, July, '95. Shortened version with minor correction

On the Wilsonian renormalization group equation for nuclear current operators

We present the solution to the recently derived Wilsonian renormalization group (RG) equation for nuclear current operators. In order to eliminate the present ambiguity in the RG equation itself, we introduce a new condition specifying the cutoff independence of the five point Green function corresponding to the two-body propagator with current operator insertion. The resulting effective current operator is then shown to obey a modified Ward-Takahashi identity which differs from the usual one, but that nevertheless leads to current conservation.Comment: 12 page

Subtleties of Lorentz Invariance in Relativistic Constituent Quark Models of the Nucleon and the Spin-Dependent Quark Density

We study the effects of a barely perceivable violation of Lorentz invariance on results computed using a relativistic constituent quark model wave function. The model nucleon wave function of Gross {\it et al.} is constructed such thatthere is no orbital angular momentum and that the spin-dependent density is spherical. This model wave function is claimed to be manifestly covariant, but we show that this is not so. In particular,the seeming covariance of the matrix elements of the electromagnetic current arises from using the Breit frame. Matrix elements have a different appearance in any other frame.Comment: 7 pages, replacement includes further explanations and an acknowledgement to Prof. Franz Gros