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Register a new userQuasiparticle RPA with finite rank approximation for Skyrme interactions
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A.P. Severyukhin
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A finite rank separable approximation for the particle-hole RPA calculations with Skyrme interactions is extended to take into account the pairing. As an illustration of the method energies and transition probabilities for the quadrupole and octupole excitations in some O, Ar, Sn and Pb isotopes are calculated. The values obtained within our approach are very close to those that were calculated within QRPA with the full Skyrme interaction. They are in reasonable agreement with experimental data.
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A finite rank separable approximation for the quasiparticle RPA with Skyrme interactions is applied to study the low lying quadrupole and octupole states in some S isotopes and giant resonances in some spherical nuclei. It is shown that characteristics calculated within the suggested approach are in a good agreement with available experimental data.
A finite rank separable approximation for the quasiparticle RPA calculations with Skyrme interactions that was proposed in our previous work is extended to take into account the coupling between one- and two-phonon terms in the wave functions of excited states. It is shown that characteristics calculated within the suggested approach are in a good agreement with available experimental data.
We have developed a fully consistent framework for calculations in the Quasiparticle Random Phase Approximation (QRPA) with $NN$ interactions from the Similarity Renormalization Group (SRG) and other unitary transformations of realistic interactions. The consistency of our calculations, which use the same Hamiltonian to determine the Hartree-Fock-Bogoliubov (HFB) ground states and the residual interaction for QRPA, guarantees an excellent decoupling of spurious strength, without the need for empirical corrections. While work is under way to include SRG-evolved 3N interactions, we presently account for some 3N effects by means of a linearly density-dependent interaction, whose strength is adjusted to reproduce the charge radii of closed-shell nuclei across the whole nuclear chart. As a first application, we perform a survey of the monopole, dipole, and quadrupole response of the calcium isotopic chain and of the underlying single-particle spectra, focusing on how their properties depend on the SRG parameter $lambda$. Unrealistic spin-orbit splittings suggest that spin-orbit terms from the 3N interaction are called for. Nevertheless, our general findings are comparable to results from phenomenological QRPA calculations using Skyrme or Gogny energy density functionals. Potentially interesting phenomena related to low-lying strength warrant more systematic investigations in the future.
We examine the response of closed-shell nuclei using a correlated interaction, derived with the Unitary Correlation Operator Method (UCOM) from the Argonne V18 potential, in second RPA (SRPA) calculations. The same correlated two-body interaction is used to derive the Hartree-Fock ground state and the SRPA equations. Our results show that the coupling of particle-hole states to higher-order configurations produces sizable effects compared with first-order RPA. A much improved description of the isovector dipole and isoscalar quadrupole resonances is obtained, thanks in part to the more fundamental treatment of the nucleon effective mass offered by SRPA. The present work suggests the prospect of describing giant resonance properties realistically and consistently within extended RPA theories. Self-consistency issues of the present SRPA method and residual three-body effects are pointed out.
The E1(T=1) isovector dipole giant resonance (GDR) in heavy and super-heavy deformed nuclei is analyzed over a sample of 18 rare-earth nuclei, 4 actinides and three chains of super-heavy elements (Z=102, 114 and 120). Basis of the description is self-consistent separable RPA (SRPA) using the Skyrme force SLy6. The self-consistent model well reproduces the experimental data (energies and widths) in the rare-earth and actinide region. The trend of the resonance peak energies follows the estimates from collective models, showing a bias to the volume mode for the rare-earths isotopes and a mix of volume and surface modes for actinides and super-heavy elements. The widths of the GDR are mainly determined by the Landau fragmentation which in turn is found to be strongly influenced by deformation. A deformation splitting of the GDR can contribute about one third to the width and about 1 MeV further broadening can be associated to mechanism beyond the mean-field description (escape, coupling with complex configurations).
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