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 polarizabilities of the proton. While for the transition polarizabilities γE1M2, γM1E2 we recover the results of strict chiral perturbation theory, for the diagonal γE1E1, γM1M1 elements we find significant effects from rescattering.