Mesonic degrees of freedom in nuclei and retardation effects in meson-exchange currents

In the present paper we give a brief review of a consistent calculation of meson-exchange effects. For the charge density these currents are calculated up to the order of $\text{O(}\text{1}\text{M}{}^3\text{)}$ for π, ρ- and ω-exchange. The retardation currents arising from the recoil and wave function reorthonormalization currents are derived. A quantitative discussion of the retardation currents is done for the example of the deuteron form factors. As for the quadrupole form factor the retardation contribution is shown to be important. In the case of the charge form factor these effects are unimportant for our choice of deuteron wave functions.