86 research outputs found
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
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