96 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.
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
Investigating the barriers to adopting a 'human-in-nature' view in Greek biodiversity conservation
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Exact magnetohydrodynamic equilibria with flow and effects on the Shafranov shift
Exact solutions of the equation governing the equilibrium magetohydrodynamic
states of an axisymmetric plasma with incompressible flows of arbitrary
direction [H. Tasso and G.N.Throumoulopoulos, Phys. Pasmas {\bf 5}, 2378
(1998)] are constructed for toroidal current density profiles peaked on the
magnetic axis in connection with the ansatz , where ( is a parameter, labels the magnetic surfaces;
and are the density and the electrostatic potential,
respectively). They pertain to either unbounded plasmas of astrophysical
concern or bounded plasmas of arbitrary aspect ratio. For , a case which
includes flows parallel to the magnetic field, the solutions are expressed in
terms of Kummer functions while for in terms of Airy functions. On
the basis of a tokamak solution with describing a plasma surrounded
by a perfectly conducted boundary of rectangular cross-section it turns out
that the Shafranov shift is a decreasing function which can vanish for a
positive value of . This value is larger the smaller the aspect ratio of the
configuration.Comment: 13 pages, 2 figures. v2:Eq (3) has been corrected. A new figure (Fig.
2) has been added in order to illustrate u-contours in connection with
solution (24) and the Shafranov shift. Also, a sentence referring to Fig. 2
has been added after Eq. (25
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
Selection rules in the double beta decay of deformed nuclei
The 2 nu double beta decay half-lives of six nuclei, whose decays were
previously reported as theoretically forbidden, are calculated by including the
pairing interaction, which mixes different occupations and opens up the
possibility of the decay. All allowed channels for the 0 nu double beta decay
are also computed. The estimated 2 nu double beta half-lives suggest that
measurements in 244Pu may find positive signals, and that planned experiments
would succeed in detecting the 2 nu double beta decay in 160Gd. Limits for the
zero neutrino mode, in the analyzed deformed emitters, are predicted.Comment: 4 pages, 4 table
Neutrinoless Double Beta Decay in Heavy Deformed Nuclei
The zero neutrino mode of the double beta decay in heavy deformed nuclei is
investigated in the framework of the pseudo SU(3) model, which has provided an
accurate description of collective nuclear structure and predicted half-lives
for the two neutrino mode in good agreement with experiments. In the case of
the calculated zero neutrino half-life is at least three orders of
magnitude greater than the two neutrino one, giving strong support of the
identification of the radiochemically determined half-life as being the two
neutrino double beta decay. For the zero neutrino matrix elements
are of the order of magnitude of, but lesser than, those evaluated using the
QRPA. This result confirms that different nuclear models produce similar zero
neutrino matrix elements, contrary to the two neutrino case. Using these pseudo
SU(3) results and the upper limit for the neutrino mass we estimate the
half-lives for six nuclei. An upper limit for majoron
coupling constant is extracted from the experimental data.Comment: 19 pages, LaTeX, 2 figures not included, availables as poscript files
upon reques
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