Double beta decay is indispensable to solve the question of the neutrino mass
matrix together with neutrino oscillation experiments. The most sensitive
experiment since eight years - the Heidelberg-Moscow experiment in Gran-Sasso -
already now, with the experimental limit of < 0.26 eV excludes
degenerate neutrino mass scenarios allowing neutrinos as hot dark matter in the
universe for the small angle MSW solution of the solar neutrino problem. It
probes cosmological models including hot dark matter already now on the level
of future satellite experiments MAP and PLANCK. It further probes many topics
of beyond Standard Model physics at the TeV scale. Future experiments should
give access to the multi-TeV range and complement on many ways the search for
new physics at future colliders like LHC and NLC. For neutrino physics some of
them (GENIUS) will allow to test almost all neutrino mass scenarios allowed by
the present neutrino oscillation experiments. A GENIUS Test Facility has just
been funded and will come into operation by end of 2001.Comment: 16 pages, revtex, 8 figures, Talk was presented at the second
Workshop on "Neutrino Oscillations and Their Origin", NOON'2000, Dec. 6-8
(2000) Tokyo, Japan, ed: Y. Suzuki et al. World Scientific, Singapore (2001);
Home Page of Heidelberg-Moscow Experiment:
http://www.mpi-hd.mpg.de/non_acc/Talks.htm
