Retardation effects on the Efimov states

The retardation effect causes a small but finite change in the two-body pot ential, which in turn results in a large reduction in the scattering length A when the strength is near its critical value for forming a zero-energy b ound state. This coupling to the vacuum fluctuation field thus affects the two-body dynamics such that the Efimov phenomenon is destroyed. Enhanced re sponse of the scattering length Delta A for a small change in the two-body potential may be employed to gain efficiency and accuracy in experiments; f or example, in testing body bound states in a cold atomic gas. The retardat ion effect can remove several Efimov bound states, depending on how large t he change in scattering length is. Manipulation of the two-body potential b y external fields is suggested to modify or eliminate some Efimov states. T he optimal choice suggested from this analysis is to manipulate A such that A/Delta A much less than 1. Also included is a discussion on the additivit y correction to the two-body polarization potential due to the Casimir effe ct. [S1050-2947(99)04309-7].