General behavior of double beta decay amplitudes in the quasiparticle random phase approximation.

Simple formulae for the 0+ → 0+ double beta decay matrix elements, as a function of the particle-particle strength gpp, have been designed within the quasiparticle random phase approximation. The 2ν amplitude is a bilinear function of gpp, and all 0ν moments behave as ratios of a linear function and the square root of another linear function of gpp. It is suggested that these results are of general validity and that any modifications of the nuclear hamiltonian or the configuration space cannot lead to a different functional dependence.