Search

The Goldberger-Miyazawa-Oehme sum rule is used to extract the pion-nucleon coupling constant from experimental $\pi$N information. Chiral perturbation theory is exploited in relating the pionic hydrogen s-wave level shift and width results to the appropriate scattering lengths. The deduced value for the coupling is $f^2 = 0.075 \pm 0.002$, where the largest source of uncertainty is the determination of the s-wave $\pi^- p$ scattering length from the atomic level shift measurement., Comment: 4 pages, 1 figure. v2: Revised the second last paragraph of 5th section and clarified the electromagnetic corrections (Tromborg vs. $\chi$PT). Also removed the KH80 slope from the fig. 1

A brief review of the pion-nucleon sigma-term is given. Aspects of both chiral perturbation theory and phenomenology are discussed., Comment: 6 pages, 9th International Symposium on Meson-Nucleon Physics and the Structure of the Nucleon, 26-31 July, 2001, Washington D.C

Most of the data from the meson factories were available only after the $\pi N$ partial wave analysis of Koch and Pietarinen was published over 20 years ago. Since then, both the experimental precision and the theoretical framework have evolved a lot as well as the computing technology. Both the new and the earlier data are to be analysed by a highly modernised version of the earlier approach. Especially the propagation of the measurement errors in the analysis will be considered in detail, visualisation tools will be developed using the Python/Tkinter combination, and the huge data base of experiments will be handled by MySQL., Comment: 6 pages, 1 figure. For the proceedings of Menu 2001, Washington DC, Jul. 26-31, 2001

We consider sigma-terms in $\pi\pi$, $\pi N$ and $K N$ scattering. While the state of the art in $\pi\pi$ is in principle crystal clear, the kaon-nucleon case is largely unexplored. The pion-nucleon system is in-between. We propose a list of topics to be investigated in kaon-nucleon scattering, in order to make optimal use of the precision data expected from DEAR., Comment: 10 pages (LaTex). Invited talk given at the Workshop "Physics and Detectors for DAFNE", Frascati, Nov. 16-19, 1999

A brief introduction to different determinations of the piNN coupling constant is given, and some comments on the topics discussed in the working group are made., Comment: 6 pages, 3 figures, 8th International Symposium on Meson-Nucleon Physics and the Structure of the Nucleon, Zuoz, Switzerland, Aug. 15-21, 1999

A brief discussion of the elastic pion-pion scattering amplitude to two loops in chiral perturbation theory is given. Some technical details of the evaluation of two-loop diagrams are addressed, and results relevant for the pionium decay are presented., Comment: 8 pages, 2 figures, Proc. Int. Workshop Hadronic Atoms and Positronium in the Standard Model, Dubna, Russia, May 26-31, 1998

We consider chiral perturbation theory in the meson sector at order $E^6$. In the terminology of the external field technique, the two--loop graphs so generated are of the sunset type. We discuss the evaluation of several of these in the case where the masses of the particles running in the loops are equal. In particular, we present integral representations that are suitable for the evaluation of diagrams in kinematical regions where branch points and cuts are present., Comment: 28 pages, LaTeX, 5 figures embedded with epsf.sty

This is the summary of the working group on $\pi\pi$ and $\pi$N interactions of the Chiral Dynamics Workshop in Mainz, September 1-5, 1997. Each talk is represented by an extended one page abstract. Some additional remarks by the convenors are added, Comment: 20 pp, LaTeX2e, uses epsf, 1 fig

A dispersion framework, appropriate for discussing the low-energy pion-nucleon interaction, is reviewed. Sensitivity of the isoscalar D-amplitude at the unphysical Cheng-Dashen point to input from different phase shift analyses and low-energy experiments is discussed., Comment: 6 pages, no figures

We present technical details of the evaluation of the elastic pi-pi scattering amplitude to two loops in chiral perturbation theory. In particular, we elaborate on the renormalization procedure at the two-loop order and on the evaluation of the relevant Feynman diagrams that can all be expressed in terms of elementary functions. For the sake of clarity, we discuss these matters both in the N-component $\phi^4$ theory (in its symmetric phase) and in chiral perturbation theory. Estimates for the relevant low-energy constants of $O(p^6)$ are presented. Threshold parameters and phase shifts are then calculated for two sets of $O(p^4)$ coupling constants and compared with experiment. We comment on the extraction of threshold parameters from phase shift data., Comment: LaTeX, uses epsf.sty, 10 figures, 52 pages

We evaluate analytically the elastic $\pi\pi$ scattering amplitude to two loops in chiral perturbation theory and give numerical values for the two $S$--wave scattering lengths and for the phase shift difference $\delta_0^0-\delta_1^1$., Comment: 10 pages, LaTeX, uses epsfig.sty, one postscript picture included. Full postscript file available at http/www.nordita.dk/locinfo/preprints/95077.ps.gz

Energies of four-quark systems have been extracted in a static quenched SU(2) lattice Monte Carlo calculation for six different geometries, both planar and non-planar, with $\beta=2.4$ and lattice size $16^3\times 32$. In all cases, it is found that the binding energy is greatly enhanced when the four quarks can be partitioned in two ways with comparable energies. Also it is shown that the energies of the four-quark states cannot be understood simply in terms of two-quark potentials., Comment: (32 pages Latex with Bib-sty included - 3 figures not included - sent on request) Preprint HU-TFT-94-7 and LTH 330

We evaluate the amplitude for $\gamma \gamma \rightarrow \pi^0 \pi^0$ to two loops in chiral perturbation theory. The three new counterterms which enter at this order in the low-energy expansion are estimated with resonance saturation. We find that the cross section agrees rather well with the available data and with dispersion theoretic calculations even substantially above threshold. Numerical results for the Compton cross section and for the neutral pion polarizabilities are also given to two-loop accuracy., Comment: 48 pages, LaTex, 11 figs. (figures not included; available upon request from sainio@finuhcb.bitnet),BUTP-93/18,LNF-93/077(P),PSI-PR-93-17

Energies of four-quark systems have been extracted in a quenched SU(2) lattice Monte Carlo calculation for two different geometries, rectangular and colinear, with $\beta=2.4$ and lattice size $16^3\times 32$. Also, by going to a lattice $24^3\times 32$ and to $\beta=2.5$, the effect of the finite lattice size and scaling are checked. An attempt is made to understand these results in terms of a model based on interquark two-body potentials but modified very significantly by a phenomenological gluon-field overlap factor., Comment: (Latex 36 pages, bib-sty included, 8 figures not included - sent on request)