The Mean Square Radius of Deuteron in the Bethe-Salpeter Formalism

We investigate the mean square radius of the deuteron in the Bethe-Salpeter formalism with Lorentz covariance. All possible relativistic effects are considered within the additive current concerning the constituent nucleons. We argue the possibilities to explain the discrepancy in the mean square radius of the deuteron between experiment and non-relativistic nuclear potential models. It is found that the relativistic corrections cannot account for the discrepancy, since the relevant relativistic corrections cancel each other. For the relativistic corrections to the non-relativistic theory, it is necessary to have at least a consistent treatment of both the equation and the electromag· netic current of the deuteron as a bound system. Furthermore, we estimate the contributions of the off-shell effects for the photon-nucleon interaction vertex. These off-shell effects may be candidates to explain the discrepancy.