The electric dipole response of even-even 154-164Dy isotopes

The excitation of pygmy dipole resonance (PDR) and giant dipole resonance (GDR) in even-even 154-164Dy isotopes is examined through quasiparticle random-phase approximation (QRPA) with the effective interactions that restores the broken translational and Galilean invariances. In each isotope, an electric response emerges by showing ample distribution at energies below and above 10 MeV. We, therefore, study the transition cross sections and probabilities, photon strength functions, transition strengths, isospin character, and collectivity of the predicted E1 responses.

Estimation of nuclear matrix elements of double-$$\varvec{\beta }$$ decay from shell model and quasiparticle random-phase approximation

The nuclear matrix element (NME) of neutrinoless double-$$\beta $$ β ($$0\nu \beta \beta $$ 0 ν β β ) decay is an essential input for determining the neutrino effective mass, if the half-life of this decay is measured. Reliable calculation of this NME has been a long-standing problem because of the diversity of the predicted values of the NME, which depends on the calculation method. In this study, we focus on the shell model and the QRPA. The shell model has a rich amount of the many-particle many-hole correlations, and the quasiparticle random-phase approximation (QRPA) can obtain the convergence of the calculation results with respect to the extension of the single-particle space. It is difficult for the shell model to obtain the convergence of the $$0\nu \beta \beta $$ 0 ν β β NME with respect to the valence single-particle space. The many-body correlations of the QRPA may be insufficient, depending on the nuclei. We propose a new method to phenomenologically modify the results of the shell model and the QRPA compensating for the insufficiencies of each method using the information of other methods in a complementary manner. Extrapolations of the components of the $$0\nu \beta \beta $$ 0 ν β β NME of the shell model are made toward a very large valence single-particle space. We introduce a modification factor to the components of the $$0\nu \beta \beta $$ 0 ν β β NME of the QRPA. Our modification method yields similar values of the $$0\nu \beta \beta $$ 0 ν β β NME for the two methods with respect to $$^{48}$$ 48 Ca. The NME of the two-neutrino double-$$\beta $$ β decay is also modified in a similar but simpler manner, and the consistency of the two methods is improved.

Comparison of Microscopic Interacting Boson Model and Quasiparticle Random Phase Approximation 0νββ Decay Nuclear Matrix Elements

The fundamental nature of the neutrino is presently a subject of great interest. A way to access the absolute mass scale and the fundamental nature of the neutrino is to utilize the atomic nuclei through their rare decays, the neutrinoless double beta (0νββ) decay in particular. The experimentally measurable observable is the half-life of the decay, which can be factorized to consist of phase space factor, axial vector coupling constant, nuclear matrix element, and function containing physics beyond the standard model. Thus reliable description of nuclear matrix element is of crucial importance in order to extract information governed by the function containing physics beyond the standard model, neutrino mass parameter in particular. Comparison of double beta decay nuclear matrix elements obtained using microscopic interacting boson model (IBM-2) and quasiparticle random phase approximation (QRPA) has revealed close correspondence, even though the assumptions in these two models are rather different. The origin of this compatibility is not yet clear, and thorough investigation of decomposed matrix elements in terms of different contributions arising from induced currents and the finite nucleon size is expected to contribute to more accurate values for the double beta decay nuclear matrix elements. Such comparison is performed using detailed calculations on both models and obtained results are then discussed together with recent experimental results.

Comparative Analysis of Nuclear Matrix Elements of 0νβ+β+ Decay and Muon Capture in 106Cd

Comparative analyses of the nuclear matrix elements (NMEs) related to the 0νβ+β+ decay of 106Cd to the ground state of 106Pd and the ordinary muon capture (OMC) in 106Cd are performed. This is the first time the OMC NMEs are studied for a nucleus decaying via positron-emitting/electron-capture modes of double beta decay. All the present calculations are based on the proton-neutron quasiparticle random-phase approximation with large no-core single-particle bases and realistic two-nucleon interactions. The effect of the particle-particle interaction parameter gpp of pnQRPA on the NMEs is discussed. In the case of the OMC, the effect of different bound-muon wave functions is studied.

Theoretical investigation of giant dipole resonance in 146−152Nd isotopes with QRPA

We investigate the electric dipole ([Formula: see text]) structure properties of the deformed [Formula: see text]Nd nuclei in the giant dipole resonance (GDR) region within the framework of the quasiparticle random-phase approximation (QRPA). Translational and Galilean invariance (TGI) QRPA with separable isovector dipole–dipole residual interaction have been employed for the calculations. We have computed the photoabsorption cross-section and then we have compared with the experimental data. Our calculations revealed that while the photoabsorption cross-section shows a Lorentzian line in the neighborhood of spherical geometry, it starts to shift to an asymmetric shape by increasing deformation in [Formula: see text]Nd isotopes by increasing neutron number. In addition to this, we have also observed that the splitting of the [Formula: see text] strength distribution and the separation between [Formula: see text] and [Formula: see text] branches are increasing. We have calculated the contribution of the electric and magnetic parts of total dipole strength up to 20[Formula: see text]MeV for the nuclei of interest. This calculation shows that the electric part dominates the total dipole strength and [Formula: see text] excitation dominates the electric part.