CHIRAL LAGRANGIAN APPROACH TO EXCHANGE VECTOR CURRENTS IN NUCLEI

Nuclear exchange vector currents applicable to any finite nucleus are calculated up to one-loop order (corresponding to next-to-next-to-lead ing order) in chiral perturbation theory. As an illustration of the po wer of the approach, we apply the formalism to the classic nuclear pro cess n + p --> d + gamma at thermal energy. The exchange current corre ction comes out to be (4.5 +/- 0.3)% in amplitude giving a predicted c ross section sigma = (334 +/- 3)mb in excellent agreement with the exp erimental value (334.2 +/- 0.5) mb. Together with the axial charge tra nsitions computed previously, this result provides strong support for the power of chiral Lagrangians in nuclear physics. Certain aspects pe rtinent to heavy nuclei are also discussed. A by-product of our result s is an open problem only partially addressed in the paper in the appl ication of the chiral Lagrangian approach to nuclear processes that ha s to do with giving a physical meaning to the short-range correlations that play an important role in nuclei.