TTP96-12 BINARY BOOSTS

The relativistic motion of an isolated two–body system (bound or unbound) of given lab energy $K^{0}$ in QED is separated into cms motion and relative motion. The relative motion equation ${\cal K}_{L}} \psi_{L} ({\bf r}_{L} ) =0$ contains the momentum eigenvalue ${\bf K}$ of the cms motion. It is greatly simplified by a binary boost to the atomic rest frame, where $K^{0}$ and ${\bf K}$ appear only in a Lorentz–invariant combination. This boost is not a product of single–particle boosts, which are useful only for perturbative interactions. CPT–invariance is demonstrated, and orthogonality