We reconsider the Dirac-Foldy contribution $\mu^2/m$ to the neutron electric polarizability. Using a Dirac equation approach to neutron-nucleus scattering, we review the definitions of Compton continuum ($\bar{ \alpha}$), classical static ($\alpha^n_E$), and Schr\"{ o}dinger ($\alpha_{ Sch}$) polarizabilities and discuss in some detail their relationship. The latter $\alpha_{ Sch}$ is the value of the neutron electric polarizability as obtained from an analysis using the Schr\"{ o}dinger equation. We find in particular $\alpha_{ Sch} = \bar{ \alpha} - \mu^2/m$ , where $\mu$ is the magnitude of the magnetic moment of a neutron of mass $m$. However, we argue that the static polarizability $\alpha^n_E$ is correctly defined in the rest frame of the particle, leading to the conclusion that twice the Dirac-Foldy contribution should be added to $\alpha_{ Sch}$ to obtain the static polarizability $\alpha^n_E$.
Categories: nucl-th hep-ph