Error estimates for pi-pi scattering threshold parameters in Chiral Perturbation Theory to two loops

Using the analysis of ChPT to two loops, we perform an error analysis of the threshold and low energy parameters, based on the uncertainties for the one loop low energy parameters and the resonance saturation mechanism. Different sets of one loop low energy constants have been considered.Thus, the predictive power of the effective field theory is quantified on the basis of the present experimental uncertainties.Comment: 12 pages, 2 tables, 3 figures. Numerics upgraded to v2 of ref.(8). New reference added. Typos corrected. New figure for SU(3) parameters include

pp→ppωpp\to pp\omega reaction near threshold

We analyze the total cross section data for $pp \to pp\omega$ near threshold measured recently at SATURNE. Using an effective range approximation for the on-shell $pp$ S-wave final state interaction we extract from these data the modulus $|\Omega| = 0.53$ fm$^4$ of the threshold transition amplitude $\Omega$. We present a calculation of various (tree-level) meson exchange diagrams contributing to $\Omega$. It is essential that $\omega$-emission from the anomalous $\omega\rho\pi$-vertex interferes destructively with $\omega$-emission from the proton lines. The contribution of scalar $\sigma$-meson exchange to $\Omega$ turns out to be negligibly small. Without introducing off-shell meson-nucleon form factors the experimental value $|\Omega|=0.53$ fm$^4$ can be reproduced with an $\omega N$-coupling constant of $g_{\omega N}=10.7$. The results of the present approach agree qualitatively with the J\"ulich model. We also perform a combined analysis of the reactions $pp\to pp\pi^0, pn\pi^+, pp\eta, pp\omega$ and $pn\to pn\eta$ near threshold.Comment: Latex-file 6 pages, 2 Figure

Chiral corrections to kaon-nucleon scattering lengths

We calculate the threshold T-matrices of kaon-nucleon and antikaon-nucleon scattering to one loop order in SU(3) heavy baryon chiral perturbation theory. To that order the complex-valued isospin-1 $\bar KN$ threshold T-matrix can be successfully predicted from the isospin-0 and 1 $KN$ threshold T-matrices. As expected perturbation theory fails to explain the isospin-0 $\bar KN$ threshold T-matrix which is completely dominated by the nearby subthreshold $\Lambda^*(1405)$-resonance. Cancelations of large terms of second and third chiral order are observed as they seem to be typical for SU(3) baryon chiral perturbation theory calculations. We also give the kaon and eta loop corrections to the $\pi N$ scattering lengths and we investigate $\pi\Lambda$ scattering to one-loop order. The second order s-wave low-energy constants are all of natural size and do not exceed 1 GeV$^{-1}$ in magnitude.Comment: 8 pages, 2 figures, published in Phys. Rev. C64, 045204 (2001), corrections of numerical prefactors in Eqs.(10,11,12

One-rank interaction kernel of the two-nucleon system for medium and high energies

A new version of the separable kernel of the nucleon-nucleon interaction in the Bethe-Salpeter approach is presented. The phase shifts are fitted to recent experimental data for singlet and uncoupled triplet partial waves of the neutron-proton scattering with total angular momenta J=0,1. The results are compared with other model calculations.Comment: 10 pages, 5 figures, 3 table

Charge-Asymmetry of the Nucleon-Nucleon Interaction

Based upon the Bonn meson-exchange model for the nucleon-nucleon ($NN$) interaction, we study systematically the charge-symmetry-breaking (CSB) of the $NN$ interaction due to nucleon mass splitting. Particular attention is payed to CSB generated by the $2\pi$-exchange contribution to the $NN$ interaction, $\pi\rho$ diagrams, and other multi-meson-exchanges. We calculate the CSB differences in the $^1S_0$ effective range parameters as well as phase shift differences in $S$, $P$ and higher partial waves up to 300 MeV lab. energy. We find a total CSB difference in the singlet scattering length of 1.6 fm which explains the empirical value accurately. The corresponding CSB phase-shift differences are appreciable at low energy in the $^1S_0$ state. In the other partial waves, the CSB splitting of the phase shifts is small and increases with energy, with typical values in the order of 0.1 deg at 300 MeV in $P$ and $D$ waves.Comment: 11 pages, RevTex, 14 figure

Testing QCD Sum Rule Techniques on the Lattice

Results for the first test of the ``crude'' QCD continuum model, commonly used in QCD Sum Rule analyses, are presented for baryon correlation functions. The QCD continuum model is found to effectively account for excited state contributions to the short-time regime of two-point correlation functions and allows the isolation of ground state properties. Confusion in the literature surrounding the physics represented in point-to-point correlation functions is also addressed. These results justify the use of the ``crude'' QCD continuum model and lend credence to the results of rigorous QCD Sum Rule analyses.Comment: Discussion of systematic uncertainties augmente

One-loop calculations of hyperon polarizabilities under the large N_c consistency condition

The spin-averaged electromagnetic polarizabilities of the hyperons $\Lambda$ and $\Sigma$ are calculated within the one-loop approximation by use of the dispersion theory. The photon and meson couplings to hyperons are determined so as to satisfy the large N_c consistency condition. It is shown that in order for the large N_c consistency condition to hold exotic hyperon states such as $\Sigma^{**}$ with I=2 and J=3/2 are required in the calculation of the magnetic polarizability of the $\Sigma$ state.Comment: 17 pages, REVTeX, no figure