CONSTRAINING ALMOST DEGENERATE 3-FLAVOR NEUTRINOS

We discuss constraints on a scenario of almost degenerate three-flavor neutrinos imposed by the solar and the atmospheric neutrino anomalies , hot dark matter, and in particular by the neutrinoless double beta d ecay experiments. It is found that in the Majorana version of the mode l the region with relatively large theta(13) is favored and the model is not compatible with the popular small-theta(12) Mikheyev-Smirnov-Wo lfenstein solution of the solar neutrino problem. A constraint on the CP-violating phases including the one characteristic to Majorana neutr inos is also obtained. The stability of our conclusion against the unc ertainty of the nuclear matrix elements of double beta decay is briefl y addressed.