Osvaldo Civitarese

Weak-interaction and nuclear-structure aspects of nuclear double beta decay

Abstract Weak-interaction and nuclear-structure aspects of double beta decay are reviewed. Starting from effective electroweak lagrangians, decay rates for the two-neutrino and neutrinoless modes of the nuclear double beta decay transitions are defined and second-order perturbative expressions for the nuclear decay amplitudes are given. Nuclear matrix elements of the relevant operators are presented, as extracted from data and from shell-model and QRPA calculations as well as from other theoretical approximations. The analysis is performed both for the two-neutrino and neutrinoless modes of the decay. The expressions for ground-state-to-ground-state and ground-state-to-excited-state transitions are presented. Updated experimental and theoretical information on β−β− decays in 48Ca, 76Ge, 82Se, 96Zr, 100Mo, 116Cd, 124Sn, 128Te, 130Te, 136Xe, 150Nd, and on β+β+, β+ EC and double EC decays in 78Kr, 92Mo, 96Ru, 106Cd, 124Xe, 130Ba, 136Ce is analyzed and compared with theoretical results. The relevance of single-beta-decay transitions feeding some of the nuclei where double-beta-decay transitions occur is pointed out. The systematics of various phase-space factors and extracted matrix elements is presented.

Review of the properties of the 0νβ−β− nuclear matrix elements

In this work we investigate general properties of the nuclear matrix elements (NMEs) related to the neutrinoless double ?? decays (0????? decays) of several nuclei of interest for double-beta-decay experiments. A summary of the values of the NMEs calculated along the years by the Jyv?skyl??La Plata collaboration is given. These NMEs are compared with those of the other available calculations and general conclusions are drawn based on these comparisons.

Neutron-proton pairing in the BCS approach

We investigate the BCS treatment of neutron-proton pairing involving time-reversed orbits. We conclude that an isospin-symmetric Hamiltonian, treated with the help of the generalized Bogolyubov transformation, fails to describe the ground state pairing properties correctly. In order for the np isovector pairs to coexist with the like-particle pairs, one has to break the isospin symmetry of the Hamiltonian by artificially increasing the strength of the np pairing interaction above its isospin-symmetric value. We briefly discuss the prescription how to choose the coupling constant of this auxiliary isospin-breaking pairing force.

Review of the properties of the 0 nu beta- beta- nuclear matrix elements

In this work we investigate general properties of the nuclear matrix elements (NMEs) related to the neutrinoless double ?? decays (0????? decays) of several nuclei of interest for double-beta-decay experiments. A summary of the values of the NMEs calculated along the years by the Jyv?skyl??La Plata collaboration is given. These NMEs are compared with those of the other available calculations and general conclusions are drawn based on these comparisons.

Double-beta decay in the pseudo SU(3) scheme

Abstract We estimate the double-beta half-life in the two-neutrino mode of several heavy deformed nuclei using the pseudo SU(3) shell-model scheme. In this approach, we used a recently developed summation procedure, avoiding the closure approximation. We find forbidden decays for five potential double-beta emitters and finite values for the half-life of six other nuclei, one of them strongly inhibited. These forbidden decays represent a possible test of our model and up to now the predictions are in good agreement with the available experimental data.

Shell-model and QRPA treatments of double beta decay

Abstract The double beta decay of a model f-shell nucleus designed to simulate real, heavier, double-beta decay candidates is calculated exactly and in the Quasiparticle Random Phase Approximation (QRPA). Several features present in QRPA treatments of real nuclei are found in the exact solution, including sensitivity to neutron-proton particle-particle and quadrupole-quadrupole forces, and to short-range nucleon-nucleon repulsion. The two-neutrino double beta decay 48 Ca → 48 Ti is then calculated in both the shell model and QRPA; a qualitative agreement between these two very different treatments is noted.

Double-beta decay of 100Mo: The deformed limit.

The double beta decay of

Nuclear Matrix Elements for Double Beta Decay in the QRPA approach: a critical review

^{100}Mo

Fermion-boson interactions and quantum algebras

to the ground state and excited states of

Gamow states as continuous linear functionals over analytical test functions

^{100}Ru