DOUBLE-BETA DECAY AND THE PROTON-NEUTRON RESIDUAL INTERACTION

The validity of the pn-QRPA and -RQRPA descriptions of double beta dec ay transition amplitudes is analyzed by using an exactly solvable mode l. It is shown that the collapse of the QRPA is physically meaningful and that it is associated with the appearance of a state with zero ene rgy in the spectrum, It is shown that in the RQRPA this particular fea ture is not present and that this approach leads to finite but otherwi se spurious results for the double beta decay transition amplitudes ne ar the point of collapse.