80 research outputs found
Distinguishing the neutrinoless double beta decay mechanisms
Many new neutrinoless double beta decay (0nbb) experiments are planned or in
preparation. If the 0nbb-decay will be detected, the key issue will be what is
the dominant mechanism of this process. By measuring only transitions to the
ground state one can not distinguish among many of the 0nbb-decay mechanisms
(the light and heavy Majorana neutrino exchange mechanisms, the trilinear
R-parity breaking mechanisms etc.). We show that if the ratio of the 0nbb-decay
half-lifes for transitions to the 0^+ first excited and ground states is
determined both theoretically and experimentally, it might be possible to
determine, which 0nbb-decay mechanisms is dominant. For that purpose the
corresponding nuclear matrix elements have to be evaluated with high
reliability. The present work is giving strong motivations for experimental
studies of the 0nbb-decay transitions to the first excited 0^+ states of the
final nuclei.Comment: 9 pages, 2 figures, Talk at the School `Neutrinos in Astro, Particle
and Nuclear Physics', Erice, September 18-26, 2001,to appear in
Prog.Part.Nucl.Phys. 48 (2002
Double Beta Decay
We review the recent developments in the field of nuclear double beta decay,
which is presently an important topic in both nuclear and particle physics. The
mechanism of lepton number violation within the neutrinoless double beta decay
is discussed in context of the problem of neutrino mixing and the R-parity
violating supersymmetric extensions of the Standard model. The problem of
reliable determination of the nuclear matrix elements governing both
two-neutrino and neutrinoless modes of the double beta decay is addressed. The
validity of different approximation schemes in the considered nuclear structure
studies is analyzed and the role of the Pauli exclusion principle for a correct
treatment of nuclear matrix elements is emphasized. The constraints on
different lepton number violating parameters like effective electron neutrino
mass, effective right-handed weak interaction parameters, effective Majoron
coupling constant and R-parity violating SUSY parameters are derived from the
best presently available experimental limits on the half life of neutrinoless
mode of this process.Comment: 32 pages, RevTex, 6 postscript figure
Improved Description of One- and Two-Hole States after Electron Capture in 163 Holmium and the Determination of the Neutrino Mass
The atomic pair 163 Holmium and 163 Dysprosium seems due to the small Q value
of about 2.3 to 2.8 keV the best case to determine the neutrino mass by
electron capture. The bolometer spectrum measures the full deexcitation energy
of Dysprosium by X rays, by Auger electrons and by the recoil of Holmium. The
spectrum has an upper energy limit given by the Q value minus the neutrino
mass. Till now this spectrum has been calculated allowing in Dysprosium
excitations with 3s1/2, 3p1/2, 4s1/2, 4p1/2, 5s1/2, 5p1/2 one-holes only.
Robertson calculated recently also the spectrum with two electron hole
excitations in Dy. He took the probability for the excitation for the second
electron hole from work of Carlson and Nestor for Z=54 Xenon. He claims, that
the bolometer spectrum with two holes is "not well enough understood to permit
a sensitive determination of the neutrino mass in this way."
The purpose of the present work is to determine the theoretical bolometer
spectrum with two hole excitations more reliably directly in holmium and
dysprosium. In addition it will be shown, that the two-hole excitations do not
complicate more the determination of the neutrino mass compared to the
situation with one-hole states only. At the Q value the highest one-hole
resonance is dominant. Under the assumption of a Lorentzian line shape one has
to fit after inclusion of the experimental spectral function of the detector
four quantities to the data: (1) The neutrino mass, (2) the energy distance of
the dominant resonance to the Q value, (3) the line witdth and (4) the strength
of the resonance. Compared to Robertson this work includes major improvements
and it shows, that a determination of the neutrino mass is difficult but not
impossible.Comment: 10 pages and 5 figure
Determinant Monte Carlo for irreducible Feynman diagrams in the strongly correlated regime
We develop a numerically exact method for the summation of irreducible
Feynman diagrams for fermionic self-energy in the thermodynamic limit. The
technique, based on the Diagrammatic Determinant Monte Carlo and its recent
extension to connected diagrams, allows us to reach high () orders of
the weak-coupling expansion for the self-energy of the two-dimensional Hubbard
model. Access to high orders reveals a non-trivial analytic structure of the
self-energy and enables its controlled reconstruction with arbitrary momentum
resolution in the nonperturbative regime of essentially strong correlations,
which has recently been reached with ultracold atoms in optical lattices.Comment: 5 pages, 4 figures, published versio
Neutrinoless Double Beta Decay of 134Xe
In view of recent great progress achieved in the experimental study of the
neutrinoless double beta decay (0nbb-decay) of 134Xe we discuss theoretical
aspects of this process. The light and heavy Majorana neutrino exchange as well
as the trilinear R-parity breaking contributions to 0nbb-decay are considered.
We show that the sensitivity of the studied process to the signal of lepton
number violation is only by factor 2-3 weaker in comparison with the 0nbb-decay
of 136Xe. The current limits on effective neutrino mass (light and heavy) and
trilinear R-parity violating parameter lambda'_111 deduced from lower limits on
the 0nbb-decay half-lifes of various nuclei are reviewed and perspectives of
the experimental verification of recently announced evidence of the 0nbb-decay
of 76Ge are discussed.Comment: 5 pages, RevTe
Neutrino Mass, Electron Capture and the Shake-off Contributions
Electron capture can determine the electron neutrino mass, while the beta
decay of Tritium measures the electron antineutrino mass and the neutrinoless
double beta decay observes the Majorana neutrino mass. Electron capture e. g.
on 163Ho plus bound electron to 163Dy* plus neutrino can determine the electron
neutrino mass from the upper end of the decay spectrum of the excited Dy*,
which is given by the Q-Value minus the neutrino mass. The Dy* states decay by
X-ray and Auger electron emissions. The total decay energy is measured in a
bolometer. These excitations have been studied by Robertson and by Faessler et
al.. In addition the daughter atom Dy can also be excited by moving in the
capture process one electron into the continuum. The escape of these continuum
electrons is automatically included in the experimental bolometer spectrum.
Recently a method developed by Intemann and Pollock was used by DeRujula and
Lusignoli for a rough estimate of this shake-off process for "s" wave electrons
in capture on 163Ho. The purpose of the present work is to give a more reliable
description of "s" wave shake-off in electron capture on Holmium. For that one
needs very accurate atomic wave functions of Ho in its ground state and excited
atomic wave functions of Dy* including a description of the continuum
electrons. In the present approach the wave functions of Ho and Dy* are
determined selfconsistently with the antisymmetrized relativistic
Dirac-Hartree-Fock approach. The relativistic continuum electron wave functions
for the ionized Dy* are obtained in the corresponding selfconsistent
Dirac-Hartree-Fock-Potential. In this improved approach shake-off can hardly be
seen after electron capture in 163Ho and thus can probably not affect the
determination of the electron neutrino mass.Comment: 20 pages, 9 figure
nuclear matrix elements and the occupancy of individual orbits
The measured occupancies of valence orbits in Ge and Se are
used as a guideline for modification of the effective mean field energies that
results in better description of these quantities. With them, in combination
with the selfconsitent renormalized quasiparticle random phase approximation
(SRQRPA) method that ensures conservation of the mean particle number in the
correlated ground state, we show that the resulting nuclear
matrix element for the Ge Se transition is reduced by
25% compared to the previous QRPA value, and therefore the difference
between the present approach and the interacting shell model predictions
becomes correspondingly smaller. Analogous modification of the mean field
energies for the A=82 system also results in a reduction of
matrix element for the Se Kr transition, making it also
closer to the shell model prediction.Comment: 9 pages, 6 figure
Structure of the two-neutrino double- decay matrix elements within perturbation theory
The two-neutrino double- Gamow-Teller and Fermi transitions are
studied within an exactly solvable model, which allows a violation of both
spin-isospin SU(4) and isospin SU(2) symmetries, and is expressed with
generators of the SO(8) group. It is found that this model reproduces the main
features of realistic calculation within the quasiparticle random-phase
approximation with isospin symmetry restoration concerning the dependence of
the two-neutrino double- decay matrix elements on isovector and
isoscalar particle-particle interactions. By using perturbation theory an
explicit dependence of the two-neutrino double- decay matrix elements on
the like-nucleon pairing, particle-particle T=0 and T=1, and particle-hole
proton-neutron interactions is obtained. It is found that double- decay
matrix elements do not depend on the mean field part of Hamiltonian and that
they are governed by a weak violation of both SU(2) and SU(4) symmetries by the
particle-particle interaction of Hamiltonian. It is pointed out that there is a
dominance of two-neutrino double- decay transition through a single
state of intermediate nucleus. The energy position of this state relative to
energies of initial and final ground states is given by a combination of
strengths of residual interactions. Further, energy-weighted Fermi and
Gamow-Teller sum rules connecting Delta Z = 2 nuclei are discussed. It is
proposed that these sum rules can be used to study the residual interactions of
the nuclear Hamiltonian, which are relevant for charge-changing nuclear
transitions.Comment: 12 pages, 4 figure
Two-neutrino double beta decay of 76Ge within deformed QRPA: A new suppression mechanism
The effect of deformation on the two-neutrino double decay (2nbb-decay) for
ground state transition 76Ge -> 76Se is studied in the framework of the
deformed QRPA with separable Gamow-Teller residual interaction. A new
suppression mechanism of the 2nbb-decay matrix element based on the difference
in deformations of the initial and final nuclei is included. An advantage of
this suppression mechanism in comparison with that associated with ground state
correlations is that it allows a simultaneous description of the single beta
and the 2nbb-decay. By performing a detail calculation of the 2nbb-decay of
76Ge, it is found that the states of intermediate nucleus lying in the region
of the Gamow-Teller resonance contribute significantly to the matrix element of
this process.Comment: 33 pages, 12 figure
Neutrino masses from R-parity non-conserving loops
We present new formulae for the neutrino masses generated by R-parity
violating interactions within minimal supersymmetric standard model. The
importance of inclusion of CP phases in the neutrino mass matrix is discussed
in detail.Comment: I've decided to move the collection of my papers to arXiv for easier
access. Talk presented at the Cracow Epiphany Conference on Neutrinos and
Dark Matter, 5-8.1.2006, Cracow, Polan
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