Dirac-Foldy term and the electromagnetic polarizability of the neutron

Abstract

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 (${\alpha }_E^n$), and Schrödinger (${\alpha }_{Sch}$) 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 Schrödinger 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 ${\alpha }_E^n$ 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 ${\alpha }_E^n$.

Comments: 11 pages, RevTeX, to appear in Physical Review C