Effective Field Theory of the Single-Nucleon Sector

We address the issue of a consistent power counting scheme in manifestly Lorentz-invariant baryon chiral perturbation theory. We discuss the inclusion of vector mesons in the calculation of the nucleon electromagnetic form factors. We comment on the chiral expansion of the nucleon mass to order O(q**6).Comment: 4 pages, talk at "Chiral Symmetry in Hadron and Nuclear Physics" (Chiral 07), Osaka, Japan, 13-16 Nov. 200

Compton scattering from a pion and off-shell effects

We discuss the most general form of the electromagnetic vertex of an off-shell pion. The framework of chiral perturbation theory is used to illustrate the representation dependence of the electromagnetic three-point Green's function. For that purpose we discuss the concept of field transformations which, in comparison with the standard Gasser and Leutwyler Lagrangian, generate equivalent Lagrangians containing additional terms at order p^4 proportional to the lowest-order equation of motion. We consider Compton scattering from a pion to show that calculations involving different off-shell effects in the s- and u-channel pole diagrams may nevertheless lead to the same on-shell Compton scattering amplitude. This is a result of the equivalence theorem which states that two equivalent Lagrangians predict the same S-matrix elements even though they may generate a different off-shell behaviour of Green's functions. We conclude that off-shell effects are not only model dependent but also representation dependent.Comment: 10 pages, RevTex, no figures, invited talk at the conference on "Perspectives in Nuclear Physics at Intermediate Energies", Trieste, Italy, 8-12 May 199

How to define physical properties of unstable particles

In the framework of effective quantum field theory we address the definition of physical quantities characterizing unstable particles. With the aid of a one-loop calculation, we study this issue in terms of the charge and the magnetic moment of a spin-1/2 resonance. By appealing to the invariance of physical observables under field redefinitions we demonstrate that physical properties of unstable particles should be extracted from the residues at complex (double) poles of the corresponding S-matrix.Comment: 11 pages, 3 figures, REVTeX

Axial, induced pseudoscalar, and pion-nucleon form factors in manifestly Lorentz-invariant chiral perturbation theory

We calculate the nucleon form factors G_A and G_P of the isovector axial-vector current and the pion-nucleon form factor G_piN in manifestly Lorentz-invariant baryon chiral perturbation theory up to and including order O(p^4). In addition to the standard treatment including the nucleon and pions, we also consider the axial-vector meson a_1 as an explicit degree of freedom. This is achieved by using the reformulated infrared renormalization scheme. We find that the inclusion of the axial-vector meson effectively results in one additional low-energy coupling constant that we determine by a fit to the data for G_A. The inclusion of the axial-vector meson results in an improved description of the experimental data for G_A, while the contribution to G_P is small.Comment: 21 pages, 9 figures, REVTeX

An ideal model of an assistive technology assessment and delivery process

The purpose of the present work is to present some aspects of the Assistive Technology Assessment (ATA) process model compatible with the Position Paper 2012 by AAATE/EASTIN. Three aspects of the ATA process will be discussed in light of three topics of the Position Paper 2012: (i) The dimensions and the measures of the User eXperience (UX) evaluation modelled in the ATA process as a way to verify the efficient and the evidence-based practices of an AT service delivery centre; (ii) The relevance of the presence of the psychologist in the multidisciplinary team of an AT service delivery centre as necessary for a complete person-centred assistive solution empowering users to make their own choices; (iii) The new profession of the psychotechnologist, who explores users needs by seeking a proper assistive solution, leading the multidisciplinary team to observe critical issues and problems. Through the foundation of the Position Paper 2012, the 1995 HEART study, the Matching Person and Technology model, the ICF framework, and the pillars of the ATA process, this paper sets forth a concept and approach that emphasise the personal factors of the individual consumer and UX as key to positively impacting a successful outcome and AT solution

Nucleon Form Factors of the Isovector Axial-Vector Current: Situation of Experiments and Theory

The theoretical and experimental status of the isovector axial-vector current form factors G_A(q^2) and G_P(q^2) of the nucleon is reviewed. We also describe a new calculation of these form factors in manifestly Lorentz-invariant chiral perturbation theory (ChPT) with the inclusion of axial-vector mesons as explicit degrees of freedom.Comment: 5 pages, 3 figures. Talk given by M. R. Schindler at the International Workshop "From Parity Violation to Hadronic Structure and more...", Milos, Greece, May 16-20, 200

A simple model illustrating the impossibility of measuring off-shell effects

We consider a simple model and make use of field transformations in Lagrangian field theories to illustrate the impossibility of measuring off-shell effects in nucleon-nucleon bremsstrahlung and related processes.Comment: 3 pages, Latex2e, uses espcrc1.sty, contribution presented at the 16th International Conference on Few-Body Problems in Physics, Taipei, Taiwan, 6-10 March 200

Generalized Polarizabilities in a Constituent Quark Model

We discuss low-energy virtual Compton scattering off the proton within the framework of a nonrelativistic constituent quark model. A simple interpretation of the spin-averaged generalized polarizabilities is given in terms of the induced electric polarization (and magnetization). Explicit predictions for the generalized polarizabilities obtained from a multipole expansion are presented for the Isgur-Karl model and are compared with results of various models.Comment: 10 pages, Latex, 2 figures, uses ws-p8-50x6-00.cls, talk given at NSTAR2001, Workshop on "The Physics of Excited Nucleons," Mainz, Germany, March 7-10, 200