arXiv subjects

N. Lyutorovich

Publications and source records attributed to N. Lyutorovich.

17 recordsLinked to original sources

arXiv2024

Description of the odd $^{249-253}$No nuclei using Skyrme functionals with modified spin-spin interaction

The Skyrme energy-density functionals with modified spin-spin interaction and pairing strength are used for description of the $^{249}$No, $^{251}$No, and $^{253}$No excited states. The results of the HFB and cranked HFB calculations taking into account the blocking effect are in reasonable agreement with the available data. For many states, including rotational and three-quasiparticle states, the results of self-consistent calculations were obtained for the first time.

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arXiv2023

Multiphonon structure of high-spin states in $^{40}$Ca, $^{90}$Zr, and $^{208}$Pb

The method of description of the high-spin states, which was previously developed and applied for the states of this type in $^{208}$Pb, is generalized for the case of the states having more complex multiphonon structure. In this method, the harmonic approximation with the renormalized phonons is used in which the phonons themselves are determined within the non-linear version of the model based on the random-phase approximation (RPA) and including both the RPA correlations and the beyond-RPA ones. The mean field and the residual interaction are derived within the framework of the self-consistent RPA from the energy-density functional of the Skyrme type. The method is applied for the analysis of the available experimental data in doubly magic $^{208}$Pb and $^{40}$Ca and in semi-magic $^{90}$Zr.

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arXiv2022

Electric and Magnetic Moments and Transition Probabilities in $^{208}$Pb $\pm 1$ Nuclei

We present moments and transition probabilities in the neighboring odd-mass nuclei of $^{208}$Pb calculated fully self-consistently from the s.p. properties of $^{208}$Pb with polarization corrections from its excitations, both given from previous Skyrme-Hartree-Fock and RPA calculations. The electric results agree nicely with the data with two very interesting exceptions. In the magnetic case we obtain similar results. We discuss also polarization contributions to the $l$-forbidden $M1$ transitions, which are, however, much too small compared to the data. With a modified external field operator which accounts effectively for mesonic and many-body effects the description of the data can be substantially improved.

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arXiv2021

Self-consistent description of high-spin states in doubly magic $^{208}$Pb

We analyze recent data on a long series of high-spin states in $^{208}$Pb with a self-consistent phonon-coupling model for nuclear excitations based on the Skyrme functionals. The model is the renormalized time-blocking approximation (RenTBA) which takes the coherent one-particle-one-hole (1p1h) states of the random-phase approximation (RPA) as starting point and develops from that more complex configurations beyond RPA. To the best of our knowledge, this is the first investigation of high spin states in $^{208}$Pb using self-consistent nuclear models. The interesting point here is that complex configurations are compulsory to describe the upper end of the long spin series at all. The data thus provide an ideal testing ground for phonon-coupling models as they give direct access to complex configurations. We find that standard Skyrme functionals which perform well in ground state properties and giant resonance excitations deliver at once an agreeable description of these high spin states.

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arXiv2020

M1 resonance in $^{208}$Pb within the self-consistent phonon-coupling model

The main goal of the paper is to investigate theoretically the experimentally observed fragmentation of the isovector $M1$ resonance in $^{208}$Pb within a self-consistent model based on an energy-density functional (EDF) of the Skyrme type. This fragmentation (spread of the $M1$ strength) is not reproduced in a conventional one-particle--one-hole ($1p1h$) random-phase approximation (RPA) and thus has to be investigated in the framework of more complicated models. However, previously applied models of this type were not self-consistent. In the present work, we use a recently developed renormalized version of the self-consistent time blocking approximation (RenTBA) in which the $1p1h\otimes$phonon configurations are included on top of the RPA $1p1h$ configurations. We have determined several sets of the parameters of the modified Skyrme EDF fitted within the RenTBA and RPA and have found the necessary condition of producing the fragmentation of the $M1$ resonance in $^{208}$Pb in our model. We present also the results of the RenTBA and RPA calculations for the first excited states of the natural parity modes in $^{208}$Pb obtained with these modified parametrizations.

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arXiv2020

Skyrme RPA for nuclear resonances: trouble with magnetic modes

We discuss major differences between electric and magnetic excitations in nuclei appearing in self-consistent calculation based on Skyrme energy-density functionals. Tools of analysis are Landau-Migdal parameters for bulk properties and RPA for resonance modes of $^{208}$Pb as representative of finite nuclei. We show that the relation between the effective mass and the effective particle-hole interaction, well known in the Landau-Migdal theory, explains the success of self-consistent calculations of electric transitions in such approaches. This effect, however, does not automatically exist in the magnetic case. This calls for further developments of the Skyrme functional in the spin channel.

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arXiv2019

Low-energy M1 excitations in $^{208}$Pb and the spin channel of the Skyrme energy-density functional

We investigate the spin dependent part of the Skyrme energy-density functional, in particular its impact on the residual particle-hole interaction in self-consistent calculations of excitations. Test cases are the low-energy M1 excitations in $^{208}$Pb treated within the self-consistent random-phase approximation based on the Skyrme energy-density functional. We investigate different parametrizations of the functionals to find out which parameters of the functional have strongest correlations with M1 properties. We explore a simple method of the modification of the spin-related parameters which delivers a better description of M1 excitations while basically maintaining the good description of ground state properties.

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arXiv2018

Excitation spectra of exotic nuclei in a self-consistent phonon-coupling model

We explore giant resonance spectra and low-lying dipole strength in the Ni and Sn chains from proton rich to very neutron rich isotopes, relevant in astrophysical reaction chains. For the theoretical description we employ the random-phase approximation (RPA) plus many-body effects through a phonon coupling model with optimized selection of phonons. The nuclear force is based on the Skyrme-Hartree-Fock energy functional carried consistently through all steps of modelling. The main effect of phonon coupling is a broadening of the spectral distributions (collisional width). This broadening is particularly dramatic for low-lying dipole strength in very neutron rich nuclei delivering there a qualitative change of the spectra.

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arXiv2017

Self-consistency in the phonon space of the particle-phonon coupling model

In the paper the non-linear generalization of the time blocking approximation (TBA) is presented. The TBA is one of the versions of the extended random-phase approximation (RPA) developed within the Green-function method and the particle-phonon coupling model. In the generalized version of the TBA the self-consistency principle is extended onto the phonon space of the model. The numerical examples show that this non-linear version of the TBA leads to the convergence of the results with respect to enlarging the phonon space of the model.

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arXiv2017

Optimizing phonon space in the phonon-coupling model

We present a new scheme to select the most relevant phonons in the phonon-coupling model, named here time-blocking approximation (TBA). The new criterion, based on the phonon-nucleon coupling strengths rather than on $B(EL)$ values, is more selective and thus produces much smaller phonon spaces in TBA. This is beneficial in two respects: first, it curbs down the computational cost, and second, it reduces the danger of double counting in the expansion basis of TBA. We use here TBA in a form where the coupling strength is regularized to keep the given Hartree-Fock ground state stable. The scheme is implemented in an RPA and TBA code based on the Skyrme energy functional. We first explore carefully the cutoff dependence with the new criterion and can work out a natural (optimal) cutoff parameter. Then we use the freshly developed and tested scheme to a survey of giant resonances and low-lying collective states in six doubly magic nuclei looking also on the dependence of the results when varying the Skyrme parametrization.

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arXiv2016

Application of an Extended Random Phase Approximation on Giant Resonances in Light, Medium and Heavy Mass Nuclei

We present results of the time blocking approximation (TBA) on giant resonances in light, medium and heavy mass nuclei. The TBA is an extension of the widely used random-phase approximation (RPA) adding complex configurations by coupling to phonon excitations. A new method for handling the single-particle continuum is developed and applied in the present calculations. We investigate in detail the dependence of the numerical results on the size of the single particle space and the number of phonons as well as on nuclear matter properties. Our approach is self-consistent, based on an energy-density functional of Skyrme type where we used seven different parameter sets. The numerical results are compared with experimental data.

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arXiv2016

The phonon-coupling model for Skyrme forces

A short review on the self-consistent RPA based on a energy-density functional of the Skyrme type is given. We also present an extension of the RPA where the coupling of phonons to the single-particle states is considered. Within this approach we present numerical results which are compared with data. The self-consistent approach is compared with the Landau-Migdal theory. Here we derive from the self-consistent $ph$ interaction, the Landau-Migdal parameters as well as their density dependence. In the Appendix a new derivation of the reduced matrix elements of the $ph$ interaction is presented.

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arXiv2014

Landau-Migdal vs. Skyrme

The magnitude and density-dependence of the non-spin dependent Landau-Migdal parameters are derived from Skyrme energy functionals and compared with the phenomenological ones. We perform RPA calculations with various approximations for the Landau-Migdal particle-hole interaction and compare them with the results obtained with the full Skyrme interaction. For the first time the next to leading order in the Landau-Migdal approach is considered in nuclear structure calculations.

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arXiv2012

Self-consistent calculations of the electric giant dipole resonances in light and heavy mass nuclei

While bulk properties of stable nuclei are successfully reproduced by mean-field theories employing effective interactions, the dependence of the centroid energy of the electric giant dipole resonance on the nucleon number A is not. This problem is cured by considering many-particle correlations beyond mean-field theory, which we do within the "Quasiparticle Time Blocking Approximation". The electric giant dipole resonances in $^{16}$O, $^{40}$Ca, and $^{208}$Pb are calculated using two new Skyrme interactions.

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arXiv2008

Description of the Giant Monopole Resonance in the Even-A $^{112-124}$Sn Isotopes within the Microscopic Model Including Quasiparticle-Phonon Coupling

We have calculated the strength distributions of the giant monopole resonance in the even-A tin isotopes (A = 112-124) which were recently measured in inelastic $α$-scattering. The calculations were performed within two microscopic models: the quasiparticle random phase approximation (QRPA) and the quasiparticle time blocking approximation which is an extension of the QRPA including quasiparticle-phonon coupling. We used a self-consistent calculational scheme based on the HF+BCS approximation. The single-particle continuum was exactly included on the RPA level. The self-consistent mean field and the effective interaction were derived from the Skyrme energy functional. In the calculations, two Skyrme force parametrizations were used. The T5 parametrization with comparatively low value of the incompressibility of infinite nuclear matter ($K_{\infty}$ = 202 MeV) gives theoretical results in good agreement with the experimental data including the resonance widths.

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arXiv2008

Self-consistent calculations within the Green's function method including particle-phonon coupling and the single-particle continuum

The Green's function method in the \emph{Quasiparticle Time Blocking Approximation} is applied to nuclear excitations in $^{132}$Sn and $^{208}$Pb. The calculations are performed self-consistently using a Skyrme interaction. The method combines the conventional RPA with an exact single-particle continuum treatment and considers in a consistent way the particle-phonon coupling. We reproduce not only the experimental values of low- and high-lying collective states but we also obtain fair agreement with the data of non-collective low-lying states that are strongly influenced by the particle-phonon coupling.

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arXiv2007

Self-consistent calculations within the Extended Theory of Finite Fermi Systems

The Extended Theory of Finite Fermi Systems(ETFFS) describes nuclear excitations considering phonons and pairing degrees of freedom, using experimental single particle energies and the effective Landau-Migdal interaction. Here we use the Skyrme interactions in order to extend the range of applicability of the ETFFS to experimentally not yet investigated short-lived isotopes. We find that Skyrme interactions which reproduce at the mean field level both ground state properties and nuclear excitations are able to describe the spreading widths of the giant resonances in the new approach, but produce shifts of the centroid energies. A renormalization of the Skyrme interactions is required for approaches going beyond the mean field level.

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