426 research outputs found
Nuclear moments for the neutrinoless double beta decay II
The recently developed formalism for the evaluation of nuclear form factors
in neutrinoless double beta decay is applied to , ,
, , and nuclei. Explicit analytical
expressions that follows from this theoretical development, in the single mode
model for the decay of , have been worked out. They are useful both
for testing the full numerical calculations, and for analytically checking the
consistency with other formalisms. Large configuration space calculations are
compared with previous studies, where alternative formulations were used. Yet,
besides using the G-matrix as residual interaction, we here use a simple
-force. Attention is paid to the connected effects of the short range
nuclear correlations and the finite nucleon size. Constraints on lepton number
violating terms in the weak Hamiltonian (effective neutrino Majorana mass and
effective right-handed current coupling strengths) are deduced.Comment: 18 pages, latex, minor changes, to appear in Nucl. Phys.
Exact evaluation of the nuclear form factor for new kinds of majoron emission in neutrinoless double beta decay
We have developed a formalism, based on the Fourier-Bessel expansion, that
facilitates the evaluation of matrix elements involving nucleon recoil
operators, such as appear in serveral exotic forms of neutrinoless double beta
decay (). The method is illustrated by applying it to the
``charged'' majoron model, which is one of the few that can hope to produce an
observable effect. From our numerical computations within the QRPA performed
for , , , and nuclei, we
test the validity of approximations made in earlier work to simplify the new
matrix elements, showing that they are accurate to within 15%. Our new method
is also suitable for computing other previously unevaluated
nuclear matrix elements.Comment: 11pp., latex, fixed minor typographical error
Conditions for detecting CP violation via neutrinoless double beta decay
Neutrinoless double beta decay data together with information on the absolute
neutrino masses obtained from the future KATRIN experiment and/or astrophysical
measurements give a chance to find CP violation in the lepton sector with
Majorana neutrinos. We derive and discuss necessary conditions which make
discovery of such CP violation possible for the future neutrino oscillation and
mass measurements data.Comment: 15 pages, 4 figures, RevTe
Double Beta Decay in pn-QRPA Model with Isospin and SU(4) Symmetry Constraints
The transition matrix elements for the double beta decays
are calculated for , , , , and
nuclei, using a -interaction. As a guide, to fix the
particle-particle interaction strengths, we exploit the fact that the missing
symmetries of the mean field approximation are restored in the random phase
approximation by the residual interaction. Thus, the T=1, S=0 and T=0, S=1
coupling strengths have been estimated by invoking the partial restoration of
the isospin and Wigner SU(4) symmetries, respectively. When this recipe is
strictly applied, the calculation is consistent with the experimental limit for
the lifetime of and it also correctly reproduces the
lifetime of . In this way, however, the two-neutrino matrix elements
for the remaining nuclei are either underestimated (for and
) or overestimated (for and ) approximately by a
factor of 3. With a comparatively small variation () of the spin-triplet
parameter, near the value suggested by the SU(4) symmetry, it is possible to
reproduce the measured in all the cases. The upper limit for
the effective neutrino mass, as obtained from the theoretical estimates of
matrix elements, is eV. The dependence of the nuclear
matrix elements on the size of the configuration space has been also analyzed.Comment: 25 pages (LaTex) and 3 figures upon request, to be published in Nucl.
Phys.
Shell Model Study of the Double Beta Decays of Ge, Se and Xe
The lifetimes for the double beta decays of Ge, Se and
Xe are calculated using very large shell model spaces. The two neutrino
matrix elements obtained are in good agreement with the present experimental
data. For eV we predict the following upper bounds to the
half-lives for the neutrinoless mode: , and . These results are the first from a new generation of Shell
Model calculations reaching O(10) dimensions
Neutrino-less Double Electron Capture - a tool to research for Majorana neutrinos
The possibility to observe the neutrino-less double decay and thus
to prove the Majorana nature of neutrino as well as provide a sensitive measure
of its mass is a major challenge of to-day's neutrino physics. As an attractive
alternative we propose to study the inverse process, the radiative
neutrino-less double electron capture . The associated monoenergetic
photon provides a convenient experimental signature. Other advantages include
the favourable ratio of the to the competing capture
rates and, very importantly, the existence of coincidence trigger to suppress
the random background. These advantages partly offset the expected longer
lifetimes. Rates for the process are calculated. High Z atoms are
strongly favoured. A resonance enhancement of the capture rates is predicted at
energy release comparable to the atomic level difference. The resonance
conditions are likely to be met for decays to excited states in final nuclei.
Candidates for such studies are considered. The experimental feasibility is
estimated and found highly encouraging.Comment: New figure added, table updated, physical background discusse
Neutrinoless Double Beta Decay within QRPA with Proton-Neutron Pairing
We have investigated the role of proton-neutron pairing in the context of the
Quasiparticle Random Phase approximation formalism. This way the neutrinoless
double beta decay matrix elements of the experimentally interesting A= 48, 76,
82, 96, 100, 116, 128, 130 and 136 systems have been calculated. We have found
that the inclusion of proton-neutron pairing influences the neutrinoless double
beta decay rates significantly, in all cases allowing for larger values of the
expectation value of light neutrino masses. Using the best presently available
experimental limits on the half life-time of neutrinoless double beta decay we
have extracted the limits on lepton number violating parameters.Comment: 16 RevTex page
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