https://doi.org/10.1140/epjst/e2008-00792-9
Double beta decays and Majorana neutrinos
Majorana neutrino masses and neutrino-less double beta decays
RCNP, Osaka University, Ibaraki, Osaka 567-0047, Japan;
National Institute of Radiological Sciences, Chiba 263-8555, Japan;
Czech Technical University in Prague, Faculty of Nuclear Sciences
and Physical Engineering, Břehová 7, Prague, Czech Republic
Corresponding author: ejiri@rcnp.osaka-u.ac.jp
Neutrino-less double beta decays (
)
are sensitive and realistic probes for studying the Majorana nature
of neutrinos (
), the -mass spectrum, the absolute 
-mass scale, the Majorana CP phases and other fundamental
properties of neutrinos and weak interactions. Current 
experiments, which use detectors with the mass sensitivity
of the order of 300 meV, study the -mass in that mass region.
Future experiments with higher sensitivities of the orders of
100 meV and 30 meV, using different nuclei and methods
(calorimetric, spectroscopic), are indispensable for establishing
in the quasi degenerate and the inverted
hierarchy mass regions. 
for ultra-high sensitivity detectors
are encouraged for studying the normal hierarchy mass region.
Theoretical and experimental studies for evaluating nuclear matrix
elements are important for extracting the sensible ν-mass from
the rate. Charge exchange reactions by means of
nuclear, electromagnetic and ν probes provide valuable data
which are used to evaluate the nuclear matrix elenments.
International collaborations for experiments and
for the matrix elements are crucial for next generation studies.
© EDP Sciences, Springer-Verlag, 2008
