We approach the calculation of the nuclear matrix element of the neutrinoless double-β decay process, considering the light-neutrino-exchange channel, by way of the realistic shell-model. In ...particular the focus of our work is spotted on the role of the short-range correlations, which should be taken into account because of the short-range repulsion of the realistic potentials. Our shell-model wave functions are calculated using an effective Hamiltonian derived from the high-precision CD-Bonn nucleon-nucleon potential, the latter renormalized by way of the so-called Vlow-k approach. The renormalization procedure decouples the repulsive high-momentum component of the potential from the low-momentum ones by the introduction of a cutoff Λ, and is employed to renormalize consistently the two-body neutrino potentials to calculate the nuclear matrix elements of candidates to this decay process in mass interval ranging from A = 76 up to A = 136. We study the dependence of the decay operator on the choice of the cutoff, and compare our results with other approaches that can be found in present literature.
Three-nucleon force and continuum play important roles in reproducing the properties of atomic nuclei around driplines. Therefore it is valuable to build up a theoretical framework where both effects ...can be taken into account to solve the nuclear Schrödinger equation. To this end, in this letter, we have expressed the chiral three-nucleon force within the continuum Berggren representation, so that bound, resonant and continuum states can be treated on an equal footing in the complex-momentum space. To reduce the model dimension and computational cost, the three-nucleon force is truncated at the normal-ordered two-body level and limited in the sd-shell model space, with the residual three-body term being neglected. We choose neutron-rich oxygen isotopes as the test ground because they have been well studied experimentally, with the neutron dripline determined. The calculations have been carried out within the Gamow shell model. The quality of our results in reproducing the properties of oxygen isotopes around the neutron dripline shows the relevance of the interplay between three-nucleon force and the coupling to continuum states. We also analyze the role played by the chiral three-nucleon force, by dissecting the contributions of the 2π exchange, 1π exchange and contact terms.
This paper discusses the derivation of an effective shell-model hamiltonian starting from a realistic nucleon–nucleon potential by way of perturbation theory. More precisely, we present the state of ...the art of this approach when the starting point is the perturbative expansion of the Qˆ-box vertex function. Questions arising from diagrammatics, intermediate-states and order-by-order convergences, and their dependence on the chosen nucleon–nucleon potential, are discussed in detail, and the results of numerical applications for the p-shell model space starting from chiral next-to-next-to-next-to-leading order potentials are shown. Moreover, an alternative graphical method to derive the effective hamiltonian, based on the Zˆ-box vertex function recently introduced by Suzuki et al., is applied to the case of a non-degenerate (0+2)ħω model space. Finally, our shell-model results are compared with the exact ones obtained from no-core shell-model calculations.
► The derivation of nuclear realistic shell-model effective hamiltonians is studied. ► Perturbation theory. ► Diagrammatics, intermediate-states and order-by-order convergences are investigated. ► Shell-model calculations in degenerate and non-degenerate model spaces are presented. ► Shell-model results are compared with the exact ones.
Electron-capture reaction rates on medium-heavy nuclei are a key ingredient to describe the evolution of core-collapse and thermonuclear supernovae. To estimate these rates it is necessary to know ...the Gamow-Teller strength distributions involved. In this paper we report some preliminary results of the calculations of Gamow-Teller strength distributions for pf-shell nuclei performed in the framework of the realistic shell model.
Abstract
The need of a reliable calculation of the nuclear matrix elements for the 0
νββ
decay has ignited a new interest about the quenching of the axial coupling constant
g
A
, a procedure ...introduced to reproduce experimental results connected with GT decays. The goal of this work is to present a preliminary study to tackle this problem within the framework of the realistic shell model.
Starting from chiral two-nucleon (2NF) and chiral three-nucleon (3NF) potentials, we present a detailed study of 17Ne, a Borromean system, with the Gamow shell model which can capture continuum ...effects. More precisely, we take advantage of the normal-ordering approach to include the 3NF and the Berggren representation to treat bound, resonant and continuum states on equal footing in a complex-momentum plane. In our framework, 3NF is essential to reproduce the Borromean structure of 17Ne, while the continuum is more crucial for the halo property of the nucleus. The two-proton halo structure is demonstrated by calculating the valence proton density and correlation density. The astrophysically interesting 3/2− excited state has its energy above the threshold of the proton emission, and therefore the two-proton decay should be expected from the state.
The low-lying structures of the midshell νg9/2 Ni isotopes 72Ni and 74Ni have been investigated at the RIBF facility in RIKEN within the EURICA collaboration. Previously unobserved low-lying states ...were accessed for the first time following β decay of the mother nuclei 72Co and 74Co. As a result, we provide a complete picture in terms of the seniority scheme up to the first (8+) levels for both nuclei. The experimental results are compared to shell-model calculations in order to define to what extent the seniority quantum number is preserved in the first neutron g9/2 shell. We find that the disappearance of the seniority isomerism in the (81+) states can be explained by a lowering of the seniority-four (6+) levels as predicted years ago. For 74Ni, the internal de-excitation pattern of the newly observed (62+) state supports a restoration of the normal seniority ordering up to spin J=4. This property, unexplained by the shell-model calculations, is in agreement with a dominance of the single-particle spherical regime near 78Ni.
Elastic-scattering processes in the
Be reaction are studied on the basis of the 2
three-body cluster model of the
Be nucleus. The
Be three-body wave function obtained by the variational method in the ...Gaussian basis is used to derive an analytic representation of nuclear-matter density distribution. The interaction potential calculated for the
Be system by the double-folding method is employed to analyze experimental data on the differential cross section for the elastic-scattering process
Be (
He,
He)
Be at collision energies between 30 and 60 MeV.
We report on the calculation of double-β decay properties of 130Te and 136Xe within the framework of the realistic shell model. The effective shell-model Hamiltonian and Gamow-Teller transition ...operator are derived by way of many-body perturbation theory, in order to not to resort to an empirical quenching of the axial coupling constant gA. The results compare well with experimental data, paving the way to the calculation of the neutrinoless double-β decay nuclear matrix element for the nuclei that are currently the experimental target for the detection of this process. In this work we investigate about the perturbative properties of our approach, and the theoretical reliability of the realistic shell model.
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