In many processes involving low momentum transfer it is fruitful to regard the nucleon as a soliton or “monopole-like” configuration of the pion field. In particular, within this framework it is possible to obtain detailed predictions for pion-nucleon scattering amplitudes and for properties of baryon resonances. One can also derive model-independent linear relations between scattering amplitud...

We apply the effective field theory approach to the three-nucleon system. In particular , we consider neutron-deuteron scattering and the triton. Precise predictions for S = 3/2 scattering are obtained in a straightforward way. In the S = 1/2 channel, however, a unique nonperturbative renormalization takes place which requires the introduction of a three-body force at leading order. We also sho...

In addition to the E2/M1 ratio of the N → ∆ transition, the electromagnetic polarizabilities and spin-polarizabilities are important structure constants of the nucleon which serve as sensitive tests of chiral perturbation theory and of models of the nucleon. Recently, these quantities have been investigated experimentally at MAMI (Mainz) by high-precision Compton scattering using hydrogen and d...

We analyze isospin breaking through quark mass differences and virtual photons in the pion– nucleon scattering lengths in all physical channels in the framework of covariant baryon chiral perturbation theory. The so-called triangle relation is found to be violated by about 1.5 %. We encounter a substantial isospin-breaking correction to neutral-pion–nucleon scattering beyond Weinberg’s predicti...

The four-nucleon bound state and scattering below three-body breakup threshold are described based on the realistic coupledchannel potential CD Bonn + ∆ which allows the excitation of a single nucleon to a ∆ isobar. The Coulomb repulsion between protons is included. In the four-nucleon system the two-baryon coupled-channel potential yields effective two-, threeand fournucleon forces, mediated b...