73 research outputs found
Threshold Two-Pion Photo- and Electroproduction: More neutrals than expected
We present an exploratory study of two pion photo-- and electroproduction off
the nucleon in the threshold region. To calculate the pertinent amplitudes, we
make use of heavy baryon chiral perturbation theory. We show that due to finite
chiral loops the production cross section for final states with two neutral
pions is considerably enhanced. The experimental implications are briefly
discussed.Comment: 23pp, plain TeX, 11 figures available upon request, CRN 94/1
The reaction at threshold in chiral perturbation theory
In the framework of heavy baryon chiral perturbation theory, we give thIn the
framework of heavy baryon chiral perturbation theory, we give the chiral
expansion for the threshold amplitudes and to
quadratic order in the pion mass. The theoretical results agree within one
standard deviation with the empirical values. We also derive a relation between
the two threshold amplitudes of the reaction and the S--wave scattering lengths, and , respectively, to order
. We show that there are uncertainties mostly related to
resonance excitation which make an accurate determination of the
scattering length from the threshold amplitudes at present
very difficult. The situation is different in the isospin two final
state. Here, the chiral series converges and one finds consistent with the one--loop chiral perturbation theory prediction.Comment: 30 pp, LaTeX file, uses epsf, 6 figures (appended), corrections in
sections 5 and 6, conclusions unchange
Consistent Calculation of the Nucleon Electromagnetic Polarizabilities in Chiral Perturbation Theory Beyond Next-to-Leading Order
We calculate the nucleons' electromagnetic polarizabilities in heavy baryon
chiral perturbation theory including all terms to order . The
chiral prediction of the electric polarizabilities for the neutron and the
proton are in good agreement with the data. In the case of the magnetic
polarizabilities the big positive contribution from the
resonance is largely cancelled by a non--analytic loop contribution of the type. This novel effect helps to understand the rather small empirical
value of the nucleons' magnetic polarizability.Comment: 10 pp, TeX, BUTP-93/22 and CRN-93-3
Reactions in the radiosensitizer misonidazole induced by low-energy (0–10 ev) electrons
PD/BD/114452/2016
UID/FIS/00068/2019
PD/00193/2012
ANR-10-LABX-0066
ANR-11-IDEX-0007Misonidazole (MISO) was considered as radiosensitizer for the treatment of hypoxic tumors. A prerequisite for entering a hypoxic cell is reduction of the drug, which may occur in the early physical-chemical stage of radiation damage. Here we study electron attachment to MISO and find that it very effectively captures low energy electrons to form the non-decomposed molecular anion. This associative attachment (AA) process is exclusively operative within a very narrow resonance right at threshold (zero electron energy). In addition, a variety of negatively charged fragments are observed in the electron energy range 0–10 eV arising from dissociative electron attachment (DEA) processes. The observed DEA reactions include single bond cleavages (formation of NO2−), multiple bond cleavages (excision of CN−) as well as complex reactions associated with rearrangement in the transitory anion and formation of new molecules (loss of a neutral H2O unit). While any of these AA and DEA processes represent a reduction of the MISO molecule, the radicals formed in the course of the DEA reactions may play an important role in the action of MISO as radiosensitizer inside the hypoxic cell. The present results may thus reveal details of the molecular description of the action of MISO in hypoxic cells.publishersversionpublishe
Chiral invariant renormalization of the pion--nucleon interaction
The leading divergences of the generating functional for Green functions of
quark currents between one--nucleon states are calculated with heat kernel
techniques. The results allow for a chiral invariant renormalization of all
two--nucleon Green functions of the pion--nucleon system to in the
low--energy expansion.Comment: 13 pages, LaTex, 2 figures in appended postscript file, Univ. Wien
preprint UWThPh-1994-
Strong and Radiative Meson Decays in a Generalized Nambu--Jona-Lasinio Model
We investigate strong and radiative meson decays in a generalized
Nambu--Jona-Lasinio model. The one loop order calculation provides a
satisfactory agreement with the data for the mesonic spectrum and for radiative
decays. Higher order effects for strong decays of and are
estimated to be large. We also discuss the role of the flavour mixing
determinantal interaction.Comment: 7 pages, LaTeX, 2 figs available upon request, CRN 92-4
Unification of the physics of nucleons and nuclei
I outline an ambitious program which aims to achieve a unified description of
nucleon and nuclear properties based on one chiral effective field theory.Comment: 9 pp, 6 figs, plenary talk at 17th International IUPAP Conference on
Few-body Problems in Physics, June 5-10, 2003, Durham, North Carolina, US
Baryons as Chiral Solitons in the Nambu--Jona-Lasinio Model
The description of baryons as chiral solitons of the Nambu--Jona--Lasinio
(NJL) model is reviewed. A motivation for the soliton description of baryons is
provided from large QCD. Rigorous results on the spontaneous breaking of
chiral symmetry in QCD are discussed. It is then argued that the NJL model
provides a fair description of low--energy hadron physics. The NJL model is
therefore employed to mimic the low--energy chiral flavor dynamics of QCD. The
model is bosonized by functional integral techniques and the physical content
of the emerging effective meson theory is discussed. In particular, its
relation to the Skyrme model is established. The static soliton solutions of
the bosonized NJL model are found, their properties discussed, and the
influence of various meson fields studied. These considerations provide strong
support of Witten's conjecture that baryons can be understood as soliton
solutions of effective meson theories. The chiral soliton of the NJL model is
then quantized in a semiclassical fashion and various static properties of the
nucleon are studied. The dominating corrections to the semiclassically
quantized soliton are investigated. Time--dependent meson fluctuations off the
chiral soliton are explored and employed to estimate the quantum corrections to
the soliton mass. Finally, hyperons are described as chiral solitons of the NJL
model. This is done in both, the collective rotational approach of Yabu and
Ando as well as in the bound state approach of Callan and Klebanov.Comment: 120 pages, uuencoded and compressed postscript file is submitted,
hardcopy available upon request
- Decays Beyond One Loop
The matrix elements for K\rightarrow \pi \pi \l \nu decays are described by
four form factors and . We complete previous calculations by
evaluating at next-to-leading order in the low-energy expansion. We then
estimate higher order contributions using dispersion relations and determine
the low-energy constants and from data on decays and
on elastic pion scattering. Finally, we present predictions for the slope of
the form factor and for total decay rates.Comment: 31 pages, LaTex, 3 figs. (two figures appended as postscript file),
BUTP-94/4,ROMF2 94/0
Resonance Contributions to the Electromagnetic Low Energy Constants of Chiral Perturbation Theory
The effective chiral Lagrangian of the strong and electromagnetic
interactions of the pseudoscalar mesons at low energies depends on a set of low
energy constants. We determine the contributions to the electromagnetic
coupling constants at order , which arise from resonances within a
photon loop. We give some implications of our results, in particular we discuss
in detail the effects on the corrections to Dashen's theorem.Comment: LaTex (uses epsfig.sty), 35 pages including 3 Postscript figures. The
complete paper is also available via anonymous ftp at
ftp://www-ttp.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints/ ; slightly enlarged
version. Accepted for publication in Nucl. Phys.
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