Spin Observables in Pion Photoproduction and Nucleon Compton Scattering from the Chiral Lagrangian and Dispersion Relations

A scheme based on the chiral Lagrangian, analyticity and unitarity is applied to spin observables in pion photoproduction and nucleon Compton scattering. Subthreshold partial-wave amplitudes are calculated in chiral perturbation theory and extrapolated beyond the threshold region imposing the micro-causality and the unitarity constraint. A reasonable description of various spin observables up to energies [Formula: see text] MeV is obtained in terms of the parameters relevant at order [Formula: see text] in the chiral Lagrangian. Nucleon spin-polarizabilities predicted in our scheme are consistent with recent measurements of double polarization asymmetries at MAMI.

UNITARITY CONSTRAINT ON GENERAL SUPERSYMMETRY ALGEBRA

The existence of massless unitary representations of the general supersymmetry algebra, which contains a vector-spinor generator, is examined. It is shown that unitary representations exist when parameters in the algebra satisfy certain relations. However, the algebra in that case turns out to be a trivial extension of the ordinary supersymmetry algebra.