We construct the complete effective chiral pion-nucleon Lagrangian to third order in small momenta based on relativistic chiral perturbation theory. We then perform the so-called heavy baryon limit and construct all terms up-to-and-including order 1/m 2 with fixed and free coefficients. As an application, we discuss in detail pionnucleon scattering. In particular, we show that for this process and to third order, the 1/m expansion of the Born graphs calculated relativistically can be recovered exactly in the heavy baryon approach without any additional momentum-dependent wave function renormalization. We fit various empirical phase shifts for pion laboratory momenta between 50 and 100 MeV. This leads to a satisfactory description of the phase shifts up to momenta of about 200 MeV. We also predict the threshold parameters, which turn out to be in good agreement with the dispersive analysis. In particular, we can sharpen the prediction for the isovector S-wave scattering length, 0.083We also consider the subthreshold parameters and give a short comparison to other calculations of πN scattering in chiral perturbation theory or modifications thereof.

No abstract

We consider the chiral expansion of the octet baryon magnetic moments in heavy baryon chiral perturbation theory including all terms which are of order $q^4$. These terms are formally of quadratic order in the quark masses. We show that despite the large non-analytic quark mass corrections to the Coleman-Glashow relations at order $q^3$, including all analytic and non-analytic corrections at order $q^4$, which in total are of moderate size, allows for a fit to the measured magnetic moments due to the appearance of counter terms with free coupling constants of natural size. In this scheme, the $\Lambda \Sigma^0$ transition moment is predicted to be $\mu_{\Lambda \Sigma^0} = (1.42 \pm 0.01) \mu_N$.Comment: 20 pp, LaTeX file, 2 figures (uses epsf), corrected versio

No abstract