Relativistic corrections to the electric polarizability of compound systems - art. no. 051601

The widely used relation <(<alpha>)over tilde> = alpha (o) + Delta alpha fo r the electric polarizability, where Delta alpha is proportional to the r.m .s. charge radius of the system, is revisited within a simple model of two spinless particles bound electromagnetically. A complete set of the relativ istic corrections to ceo following from the Breit Hamiltonian is obtained. It is shown that these corrections modify the result for a in comparison to that obtained with ao taken in the nonrelativistic approximation. We propo se that the same situation can take place in the more complicated case of h adrons. Special attention is devoted to the correct definition of the cente r-of-mass coordinates which are found to be very important.