abstract
- The sum-energy spectrum of electrons emitted in double-beta decay is a well-known diagnostic for the nature of the physics which is responsible for the decay. Three types of spectra are usually considered when these experiments are analysed: one each for the standard two-neutrino decay, the neutrinoless process and a scalar-emitting decay. It has recently been shown that two other electron spectra can be possible for scalar-emitting modes, in addition to these traditional three. One of these is softer than the Standard-Model two-neutrino decay, while the other is intermediate between this and the usual majoron-emitting spectrum. The models which predict these new spectra are generically more natural than those which predict the traditional majoron-emitting spectrum, in that they can accomodate the constraints following from the steadily improving limits on neutrinoless decay without requiring the fine-tuning that is endemic to the usual models. This article reviews the properties of the physics which can produce the new kinds of electron spectra. (Invited Talk presented to the Workshop on Double Beta Decay and Related Topics, Trento Italy, April 1995.)