74 research outputs found
Theory of the Nucleon Spin-Polarizabilities II
Following up on the plenary talk given by Ulf Mei{\ss}ner, I discuss a
generalization of the concept of nucleon spin-polarizabilities in terms of
multipole excitation/de-excitation and present an overview of the available
theoretical predictions for these elusive but interesting structure parameters
of the nucleon.Comment: 4 pages, uses World Scientific style ws-p8-50x6-00.cls; talk given at
GDH2000 meeting, Mainz, German
Nucleon Compton Scattering in Chiral Effective Field Theories
Chiral effective field theories have a long history studying the process of
Compton scattering on the nucleon. In this contribution I want to focus on the
new developments that have occured since the last Chiral Dynamics conference in
Mainz 1997. I will focus exclusively on the spin-dependent sector, where most
of the recent work has been done.Comment: 10 pages, 2 figures, uses World Scientific style ws-p8-50x6-00.cls;
plenary talk given at Chiral Dynamics 2000 meeting, Newport News, V
Chiral Effective Field Theories with explicit Spin 3/2 Degrees of Freedom---A Status Report
Recent developments in calculations of low energy nucleon properties
utilizing effective chiral field theories with explicit spin 3/2 matter fields
are presented. In particular, the role of Delta resonances in microscopic
calculations of the anomalous magnetic moments of the Nucleon is discussed and
a comparison to lattice data is performed. Furthermore, the impact of Deltas on
the isovector Pauli form factor of the Nucleon and the problems one faces in
calculations of the isovector Nucleon-Delta transition form factors are
addressed.Comment: 8 pages, Latex, 5 eps figures, uses World Scientific style
ws-p8-50x6-00.cls; talk given at NSTAR01, Mainz, German
Chiral Magnetism of the Nucleon
We study the quark mass expansion of the magnetic moments of the nucleon in a
chiral effective field theory including nucleons, pions and delta resonances as
explicit degrees of freedom. We point out that the usual powercounting applied
so far to this problem misses important quark mass structures generated via an
intermediate isovector M1 nucleon-delta transition. We propose a modified
powercounting and compare the resulting chiral extrapolation function to
available (quenched) lattice data. The extrapolation is found to work
surprisingly well, given that the lattice data result from rather large quark
masses. Our calculation raises the hope that extrapolations of lattice data
utilizing chiral effective field theory might be applicable over a wider range
in quark masses than previously thought, and we discuss some open questions in
this context. Furthermore, we observe that within the current lattice data
uncertainties the extrapolations presented here are consistent with the Pade
fit ansatz introduced by the Adelaide group a few years ago.Comment: 30 pages, Latex, 7 figure
The electromagnetic Nucleon to Delta transition in Chiral Effective Field Theory
We present a calculation of the three complex form factors parametrizing the
nucleon to Delta transition matrix element in the framework of chiral effective
field theory with explicit Delta degrees of freedom. The interplay between
short and long range physics is discussed and estimates for systematic
uncertainties due to higher order effect are given.Comment: Talk given at the 2nd international workshop "Shape of Hadrons",
April 27-29, 2006, Athens, Greec
Chiral extrapolations of nucleon properties from lattice QCD
We report on recent work about the study of quark mass dependence of nucleon
magnetic moments and axial-vector coupling constant. We examine the feasibility
of chiral effective field theory methods for the extrapolation of lattice QCD
data obtained at relative large pion masses down to the physical values.Comment: 5pages, LaTeX, 3 figures, uses World Scientific style file; presented
at PANIC 02, Osak
Chiral Analysis of the Generalized Form Factors of the Nucleon
We apply the methods of Chiral Perturbation Theory to the analysis of the
first moments of the Generalized Parton Distributions in a Nucleon, usually
known as generalized form factors. These quantities are currently also under
investigation in Lattice QCD analyses of baryon structure, providing simulation
results at large quark masses to be extrapolated to the "real world" via Chiral
Effective Field Theory. We have performed a leading-one-loop calculation in the
covariant framework of Baryon Chiral Perturbation Theory (BChPT), predicting
both the momentum and the quark-mass dependence for all the vector and axial
(generalized) form factors. In particular we discuss the results for the limit
of vanishing four-momentum transfer where the GPD-moments reduce to the well
known moments of Parton Distribution Functions (PDFs). We fit our results to
available lattice QCD data, extrapolating down to the physical point. We
conclude by presenting outstanding results from a combined fit to different
GPDs-moments.Comment: 7 pages, 4 figures, Proceedings of Lattice 2007 (July 30 - 4 August
2007, Regensburg, Germany
- …