Compton scattering from chiral dynamics with unitarity and causality
Proton Compton scattering is analyzed with the chiral Lagrangian. Partial-wave amplitudes are obtained by an analytic extrapolation of subthreshold reaction amplitudes computed in chiral perturbation theory, where the constraints set by electromagnetic-gauge invariance, causality and unitarity are used to stabilize the extrapolation. We present and discuss predictions for various spin observables and polarizabilties of the proton. While for the transition polarizabilities $\gamma_{E1M2}, \gamma_{M1E2}$ we recover the results of strict chiral perturbation theory, for the diagonal $\gamma_{E1E1}, \gamma_{M1M1}$ elements we find significant effects from rescattering.