Nucleons with chiral loops: Electromagnetic polarizabilities

We investigate the electric (α) and magnetic (β) polarizabilities to one-loop order in chiral perturbation theory. Our calculation sheds light on the two most prominent empirical features, namely that (i) the sum of the magnetic and the electric polarizabilities of the neutron and the proton are approximately the same (α_p + β_p ≈ α_n + β_n) and (ii) that the proton and the neutron behave essentially as electric dipoles (α_p,n ≫ β_p,n). Furthermore, we discuss the connection between the nucleons' polarizabilities and the pion photoproduction processes.