Meson-exchange effects in neutrinoless nuclear double beta decay

Explicit expression for the effective meson-exchange weak NN potential appropriate for the lepton number non-conserving, (0+-0+) neutrinoless nuclear double beta decay is obtained in the two-nucleon mechanism of Primakoff and Rosen. It is shown that in the case of neutrinoless nuclear double beta decay mediated by a heavy Majorana neutrino, pion-exchange effects are indeed very important and therefore must be included in nuclear matrix element calculations for the process