889 research outputs found
Non-collapsing renormalized QRPA with proton-neutron pairing for neutrinoless double beta decay
Using the renormalized quasiparticle random phase approximation (RQRPA), we
calculate the light neutrino mass mediated mode of neutrinoless double beta
decay of Ge76, Mo100, Te128 and Te130. Our results indicate that the simple
quasiboson approximation is not good enough to study the neutrinoless double
beta decay, because its solutions collapse for physical values of g_pp. We find
that extension of the Hilbert space and inclusion of the Pauli Principle in the
QRPA with proton-neutron pairing, allows us to extend our calculations beyond
the point of collapse, for physical values of the nuclear force strength. As a
consequence one might be able to extract more accurate values on the effective
neutrino mass by using the best available experimental limits on the half-life
of neutrinoless double beta decay.Comment: 15 pages, RevTex, 2 Postscript figures, to appear in Phys. Lett.
The Pauli principle, QRPA and the two-neutrino double beta decay
We examine the violation of the Pauli exclusion principle in the
Quasiparticle Random Phase Approximation (QRPA) calculation of the two-neutrino
double beta decay matrix elements, which has its origin in the quasi-boson
approximation. For that purpose we propose a new renormalized QRPA with
proton-neutron pairing method (full-RQRPA) for nuclear structure studies, which
includes ground state correlation beyond the QRPA. This is achieved by using of
renormalized quasi-boson approximation, in which the Pauli exclusion principle
is taken into account more carefully. The full-RQRPA has been applied to
two-neutrino double beta decay of , , and
. The nuclear matrix elements have been found significantly less
sensitive to the increasing strength of particle-particle interaction in the
physically interesting region in comparison with QRPA results. The strong
differences between the results of both methods indicate that the Pauli
exclusion principle plays an important role in the evaluation of the double
beta decay. The inclusion of the Pauli principle removes the difficulties with
the strong dependence on the particle-particle strength in the QRPA on
the two-neutrino double beta decay.Comment: Accepted for publication in Nucl. Phys. A, 22 pages, including 5
figures, LaTeX (using REVTeX and epsfig-style
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
A large Hilbert space QRPA and RQRPA calculation of neutrinoless double beta decay
A large Hilbert space is used for the calculation of the nuclear matrix
elements governing the light neutrino mass mediated mode of neutrinoless double
beta decay of Ge76, Mo100, Cd116, Te128 and Xe136 within the proton-neutron
quasiparticle random phase approximation (pn-QRPA) and the renormalized QRPA
with proton-neutron pairing (full-RQRPA) methods. We have found that the
nuclear matrix elements obtained with the standard pn-QRPA for several nuclear
transitions are extremely sensitive to the renormalization of the
particle-particle component of the residual interaction of the nuclear
hamiltonian. Therefore the standard pn-QRPA does not guarantee the necessary
accuracy to allow us to extract a reliable limit on the effective neutrino
mass. This behaviour, already known from the calculation of the two-neutrino
double beta decay matrix elements, manifests itself in the neutrinoless
double-beta decay but only if a large model space is used. The full-RQRPA,
which takes into account proton-neutron pairing and considers the Pauli
principle in an approximate way, offers a stable solution in the physically
acceptable region of the particle-particle strength. In this way more accurate
values on the effective neutrino mass have been deduced from the experimental
lower limits of the half-lifes of neutrinoless double beta decay.Comment: 19 pages, RevTex, 1 Postscript figur
Short-range correlations and neutrinoless double beta decay
In this work we report on the effects of short-range correlations upon the
matrix elements of neutrinoless double beta decay. We focus on the calculation
of the matrix elements of the neutrino-mass mode of neutrinoless double beta
decays of 48Ca and 76Ge. The nuclear-structure components of the calculation,
that is the participant nuclear wave functions, have been calculated in the
shell-model scheme for 48Ca and in the proton-neutron quasiparticle
random-phase approximation (pnQRPA) scheme for 76Ge. We compare the traditional
approach of using the Jastrow correlation function with the more complete
scheme of the unitary correlation operator method (UCOM). Our results indicate
that the Jastrow method vastly exaggerates the effects of short-range
correlations on the neutrinoless double beta decay nuclear matrix elements.Comment: 12 pages, 3 figures, to appear in Physics Letters B (2007
Activated Notch2 Signaling Inhibits Differentiation of Cerebellar Granule Neuron Precursors by Maintaining Proliferation
AbstractIn the developing cerebellar cortex, granule neuron precursors (GNPs) proliferate and commence differentiation in a superficial zone, the external granule layer (EGL). The molecular basis of the transition from proliferating precursors to immature differentiating neurons remains unknown. Notch signaling is an evolutionarily conserved pathway regulating the differentiation of precursor cells of many lineages. Notch2 is specifically expressed in proliferating GNPs in the EGL. Treatment of GNPs with soluble Notch ligand Jagged1, or overexpression of activated Notch2 or its downstream target HES1, maintains precursor proliferation. The addition of GNP mitogens Jagged1 or Sonic Hedgehog (Shh) upregulates the expression of HES1, suggesting a role for HES1 in maintaining precursor proliferation
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
The Neutrinoless Double Beta Decay: The Case for Germanium Detectors
An overview of the current status of Neutrinoless Double Beta Decay is
presented, emphasizing on the case of Germanium Detectors.Comment: 5 figures, Invited contribution at the XXX International Meeting on
Fundamental Physics, IMFP2002, February 2002, Jaca, Spain. To appear in Nucl.
Phys. B (Proc. Suppl
The Single State Dominance Hypothesis and the Two-Neutrino Double Beta Decay of Mo100
The hypothesis of the single state dominance (SSD) in the calculation of the
two-neutrino double beta decay of Mo100 is tested by exact consideration of the
energy denominators of the perturbation theory. Both transitions to the ground
state as well as to the 0+ and 2+ excited states of the final nucleus Ru100 are
considered. We demonstrate, that by experimental investigation of the single
electron energy distribution and the angular correlation of the outgoing
electrons, the SSD hypothesis can be confirmed or ruled out by a precise
two-neutrino double beta decay measurement (e.g. by NEMO III collaboration).Comment: 13 pages, RevTex, 1 figur
Light-neutrino mass hierarchies, nuclear matrix elements, and the observability of neutrinoless double-beta decay
Results for neutrino flavor oscillations and neutrino mixing mechanisms,
obtained from the analysis of the Sudbury Neutrino Observatory (SNO), the
SuperKamiokande (SK), CHOOZ, KamLAND and WMAP data, are used to calculate the
effective neutrino mass relevant for the neutrinoless double-beta decay. The
observability of the decay of 76Ge is discussed within different light-neutrino
mass hierarchies and by presenting a systematics on the available nuclear
matrix elements.Comment: 25 pages, 1 figur
- …