6 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
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
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
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