J. Barea

Nuclear matrix elements for double- β decay

Background: Direct determination of the neutrino mass through double-β decay is at the present time one of the most important areas of experimental and theoretical research in nuclear and particle physics. - Purpose: We calculate nuclear matrix elements for the extraction of the average neutrino mass in neutrinoless double-β decay. - Methods: The microscopic interacting boson model (IBM-2) is used. - Results: Nuclear matrix elements in the closure approximation are calculated for 48Ca, 76Ge, 82Se, 96Zr, 100Mo, 110Pd, 116Cd, 124Sn, 128Te, 130Te, 148Nd, 150Nd, 154Sm, 160Gd, and 198Pt decay. - Conclusions: Realistic predictions for the expected half-lives in neutrinoless double-β decay with light and heavy neutrino exchange in terms of neutrino masses are made and limits are set from current experiments.

0 ν β β and 2 ν β β nuclear matrix elements in the interacting boson model with isospin restoration

We introduce a method for isospin restoration in the calculation of nuclear matrix elements (NMEs) for 0 ν β β and 2 ν β β decay within the framework of the microscopic interacting boson model (IBM-2). With this method, we calculate the NMEs for all processes of interest in 0 ν β − β − and 2 ν β − β − and in 0 ν β + β + , 0 ν EC β + , R 0 ν ECEC , 2 ν β + β + , 2 ν EC β + , and 2 ν ECEC . With this method, the Fermi matrix elements for 2 ν β β vanish, and those for 0 ν β β are considerably reduced.

Limits on Neutrino Masses from Neutrinoless Double- β Decay

Neutrinoless double-β decay is of fundamental importance for the determining neutrino mass. By combining a calculation of nuclear matrix elements within the framework of the microscopic interacting boson model with an improved calculation of phase space factors, we set limits on the average light neutrino mass and on the average inverse heavy neutrino mass (flavor-violating parameter).

Nuclear Masses Set Bounds on Quantum Chaos

It has been suggested that chaotic motion inside the nucleus may significantly limit the accuracy with which nuclear masses can be calculated. Using a power spectrum analysis we show that the inclusion of additional physical contributions in mass calculations, through many-body interactions or local information, removes the chaotic signal in the discrepancies between calculated and measured masses. Furthermore, a systematic application of global mass formulas and of a set of relationships among neighboring nuclei to more than 2000 nuclear masses allows one to set an unambiguous upper bound for the average errors in calculated masses, which turn out to be almost an order of magnitude smaller than estimated chaotic components.

Phase transitions and critical points in the rare-earth region

A systematic study of isotope chains in the rare--earth region is presented. For the chains (144-154)Nd, (146-160)Sm, (148-162)Gd, and (150-166)Dy, energy levels, E2 transition rates, and two--neutron separation energies are described by using the most general (up to two--body terms) IBM Hamiltonian. For each isotope chain a general fit is performed in such a way that all parameters but one are kept fixed to describe the whole chain. In this region nuclei evolve from spherical to deformed shapes and a method based on catastrophe theory, in combination with a coherent state analysis to generate the IBM energy surfaces, is used to identify critical phase transition points.

Phase-space factors and half-life predictions for Majoron-emitting β−β− decay

A complete calculation of phase space factors (PSF) for Majoron emitting

Bounds on the presence of quantum chaos in nuclear masses

0\nu\beta^-\beta^-

Neutrinoless double-positron decay and positron-emitting electron capture in the interacting boson model

decay modes is presented. The calculation makes use of exact Dirac wave functions with finite nuclear size and electron screening and includes life-times, single electron spectra, summed electron spectra, and angular electron correlations. Combining these results with recent interacting boson nuclear matrix elements (NME) we make half-life predictions for the the ordinary Majoron decay (spectral index

Limits on sterile neutrino contributions to neutrinoless double beta decay

n

THE ART OF PREDICTING NUCLEAR MASSES

=1). Furthermore, comparing theoretical predictions with the obtained experimental lower bounds for this decay mode we are able to set limits on the effective Majoron-neutrino coupling constant