221 research outputs found
Spin Polarizabilities of the Nucleon from Polarized Low Energy Compton Scattering
As guideline for forthcoming experiments, we present predictions from Chiral
Effective Field Theory for polarized cross sections in low energy Compton
scattering for photon energies below 170 MeV, both on the proton and on the
neutron. Special interest is put on the role of the nucleon spin
polarizabilities which can be examined especially well in polarized Compton
scattering. We present a model-independent way to extract their energy
dependence and static values from experiment, interpreting our findings also in
terms of the low energy effective degrees of freedom inside the nucleon: The
polarizabilities are dominated by chiral dynamics from the pion cloud, except
for resonant multipoles, where contributions of the Delta(1232) resonance turn
out to be crucial. We therefore include it as an explicit degree of freedom. We
also identify some experimental settings which are particularly sensitive to
the spin polarizabilities.Comment: 30 pages, 19 figure
Radiative pion capture by a nucleon
The differential cross sections for and are computed up to in heavy baryon chiral perturbation
theory (HBChPT). The expressions at and have no free
parameters. There are three unknown parameters at , low energy
constants of the HBChPT Lagrangian, which are determined by fitting to
experimental data. Two acceptable fits are obtained, which can be separated by
comparing with earlier dispersion relation calculations of the inverse process.
Expressions for the multipoles, with emphasis on the p-wave multipoles, are
obtained and evaluated at threshold. Generally the results obtained from the
best of the two fits are in good agreement with the dispersion relation
predictions.Comment: 24 pages, Latex, using RevTe
N Delta - Transition Form Factors at Low Momentum Transfer
The three complex form factors entering the vertex
are calculated to in the framework of a chiral effective
theory with explicit (1232) degrees of freedom. Furthermore, the role
of presently unknown low energy constants that affect the values of EMR and CMR
is elucidated.Comment: 5 pages, 3 figures, Oral contribution given at the 8th International
Conference on the Structure of Baryons (Baryons '98), Bonn, Germany, Sept.
22-26, 199
Strange form factors and Chiral Perturbation Theory
We review the contributions of Chiral Perturbation Theory to the theoretical
understanding or not-quite-yet-understanding of the nucleon matrix elements of
the strange vector current.Comment: 4 pages, 6 figures, presented at the International Workshop on Parity
Violation and Hadronic Structure (PAVI04), Grenoble, France, 8-11 Jun 200
Complete one-loop analysis of the nucleon's spin polarizabilities
We present a complete one-loop analysis of the four nucleon spin
polarizabilities in the framework of heavy baryon chiral perturbation theory.
The first non-vanishing contributions to the isovector and first corrections to
the isoscalar spin polarizabilities are calculated. No unknown parameters enter
these predictions. We compare our results to various dispersive analyses. We
also discuss the convergence of the chiral expansion and the role of the delta
isobar.Comment: 4 pp, REVTE
- …