THEORETICAL ASPECTS OF THE POLARIZABILITY OF THE NUCLEON

Two aspects of the nucleon electromagnetic polarizabilities, alpha(N) and beta(N), are discussed. The first one is the interrelation between static and Compton polarizabilities. Relativistically consistent trea tment of the polarization effects based on effective Lagrangians resul ts in the conclusion that the Compton polarizabilities, rather than th e static ones, drive the energy shift of the nucleon in external field s. The cluster substructure of the static polarizabilities. is shown t o be crucial for consistent calculations of the polarizabilities. The second aspect concerns the dominant role of pion degrees of freedom in alpha(N) as seen through dispersion relations, chiral perturbation th eory, and constituent models. The reported calculations of alpha(N) wi thin soliton models are shown to be inconsistent with gauge invariance . The difficulties in explaining the observed large diamagnetic compon ent of beta(N) are emphasized.