145 research outputs found
Comment about pion electro-production and the axial form factors
The claim by Haberzettl (Phys.Rev.Lett.85 (2000) 3576) that the axial form
factor of the nucleon cannot be accessed through threshold pion
electroproduction is unfounded
Pion photo- and electroproduction and the partially-conserved axial current
The relevance of the axial current for pion production processes off the
nucleon with real or virtual photons is revisited. Employing the hypothesis of
a partially conserved axial current (PCAC), it is shown that, when all of the
relevant contributions are taken into account, PCAC does not provide any
additional constraint for threshold production processes that goes beyond the
Goldberger-Treiman relation. In particular, it is shown that pion
electroproduction processes at threshold cannot be used to extract any
information regarding the weak axial form factor. The relationships found in
previous investigations are seen to be an accident of the approximations
usually made in this context.Comment: 4 pages, 3 figures; typos corrected; references updated; some
rewording; conclusions unchange
Image analysis in sedimentology as application for high-resolution grain size analysis: a case study of lake sediments from Tangra Yumco (Tibetan Plateau)
Abstract HKT-ISTP 2013
B
GaBoDS: The Garching-Bonn Deep Survey -- II. Confirmation of EIS cluster candidates by weak gravitational lensing
We report the first confirmation of colour-selected galaxy cluster candidates
by means of weak gravitational lensing. Significant lensing signals were
identified in the course of the shear-selection programme of dark matter haloes
in the Garching-Bonn Deep Survey, which currently covers 20 square degrees of
deep, high-quality imaging data on the southern sky. The detection was made in
a field that was previously covered by the ESO Imaging Survey (EIS) in 1997. A
highly significant shear-selected mass-concentration perfectly coincides with
the richest EIS cluster candidate at z~0.2, thus confirming its cluster nature.
Several other shear patterns in the field can also be identified with cluster
candidates, one of which could possibly be part of a filament at z~0.45.Comment: 4 pages, 4 figures, submitted to A&A Letter
GaBoDS: The Garching-Bonn Deep Survey - III. Lyman-Break Galaxies in the Chandra Deep Field South
We present first results of our search for high-redshift galaxies in deep CCD
mosaic images. As a pilot study for a larger survey, very deep images of the
Chandra Deep Field South (CDFS), taken withWFI@MPG/ESO2.2m, are used to select
large samples of 1070 U-band and 565 B-band dropouts with the Lyman-break
method. The data of these Lyman-break galaxies are made public as an electronic
table. These objects are good candidates for galaxies at z~3 and z~4 which is
supported by their photometric redshifts. The distributions of apparent
magnitudes and the clustering properties of the two populations are analysed,
and they show good agreement to earlier studies. We see no evolution in the
comoving clustering scale length from z~3 to z~4. The techniques presented here
will be applied to a much larger sample of U-dropouts from the whole survey in
near future.Comment: 11 pages, 11 figures, replaced with version accepted by A&A. Minor
changes and tabular appendix with LBG catalogues. Version with full
resolution figures available at
http://www.astro.uni-bonn.de/~hendrik/2544.pd
On the pion electroproduction amplitude
We analyze amplitudes for the pion electroproduction on proton derived from
Lagrangians based on the local chiral SU(2) x SU(2) symmetries. We show that
such amplitudes do contain information on the nucleon axial form factor F_A in
both soft and hard pion regimes. This result invalidates recent Haberzettl's
claim that the pion electroproduction at threshold cannot be used to extract
any information regarding F_A.Comment: 14 pages, 6 figures, revised version, accepted for publication in
Phys. Rev.
J/psi production at the Tevatron and RHIC from s-channel cut
We report on our recent evaluation of the s-channel cut contribution to J/psi
hadroproduction. We show that it is likely significantly larger than the usual
cut contribution of the colour-singlet model (CSM), which is known to
underestimate the experimental measurements. Here the s-channel cut develops
for configurations with off-shell quarks in the bound state. A correct
treatment of its contribution requires the introduction of a four point
function, partially constrained by gauge invariance and limiting behaviours at
small and large momenta. When the unconstrained degrees of freedom are fixed to
reproduce the Tevatron data, we show that RHIC data are remarkably well
reproduced down to very low transverse momenta P_T without need of resummation
of initial-state gluon effects. This unique feature might be typical of
s-channel cut contribution.Comment: Presented by J.P. Lansberg at the Joint Meeting
Heidelberg-Liege-Paris-Wroclaw (HLPW08), Spa, Belgium, 6-8 March 2008, 10
pages, 8 figures, LaTeX, uses aip-6s.clo, aipproc.cls and aipxfm.sty
(included
Inclusive and exclusive photoproduction on the deuteron: - and -threshold phenomena
Inclusive and exclusive photoproduction on the deuteron are
investigated theoretically. Modern hyperon-nucleon forces and a recently
updated kaon photoproduction operator for the process are
used. Sizable effects of the hyperon-nucleon final state interaction are found
near the and thresholds in the inclusive reaction.
Angular distributions for the exclusive process show clear final state
interaction effects in certain kinematic regions. Precise data especially for
the inclusive process around the threshold would help to clarify
the strength and property of the interaction.Comment: 14 pages, 10 figure
Complex Conjugate Pairs in Stationary Sturmians
Sturmian eigenstates specified by stationary scattering boundary conditions
are particularly useful in contexts such as forming simple separable two
nucleon t matrices, and are determined via solution of generalised eigenvalue
equation using real and symmetric matrices. In general, the spectrum of such an
equation may contain complex eigenvalues. But to each complex eigenvalue there
is a corresponding conjugate partner. In studies using realistic
nucleon--nucleon potentials, and in certain positive energy intervals, these
complex conjugated pairs indeed appear in the Sturmian spectrum. However, as we
demonstrate herein, it is possible to recombine the complex conjugate pairs and
corresponding states into a new, sign--definite pair of real quantities with
which to effect separable expansions of the (real) nucleon--nucleon reactance
matrices.Comment: (REVTEX) 8 Pages, Padova DFPD 93/TH/78 and University of Melbourn
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