Collective description of nuclear double beta decay transitions

A consistent treatment of the intrinsic and collective coordinates relevant for the calculation of matrix elements describing nuclear double beta decay transitions is introduced. The method, which was originally developed for the case of nuclear rotations, is adapted to include isospin and number of particles degrees of freedom. To illustrate its main features we apply the formalism to the case of Fermi transitions in a simplified model. From the corresponding results we conclude that the uncertainties found in many existing double beta decay calculations might be largely due to the mixing of physical and spurious effects in the treatment of isospin dependent interactions.