Relativistic quasiparticle time blocking approximation: Dipole response of open-shell nuclei

Abstract

The self-consistent Relativistic Quasiparticle Random Phase Approximation (RQRPA) is extended by the quasiparticle-phonon coupling (QPC) model using the Quasiparticle Time Blocking Approximation (QTBA). The method is formulated in terms of the Bethe-Salpeter equation (BSE) in the two-quasiparticle space with an energy-dependent two-quasiparticle residual interaction. This equation is solved either in the basis of Dirac states forming the self-consistent solution of the ground state or in the momentum representation. Pairing correlations are treated within the Bardeen-Cooper-Schrieffer (BCS) model with a monopole-monopole interaction. The same NL3 set of the coupling constants generates the Dirac-Hartree-BCS single-quasiparticle spectrum, the static part of the residual two-quasiparticle interaction and the quasiparticle-phonon coupling amplitudes. A quantitative description of electric dipole excitations in the chain of tin isotopes (Z = 50) with the mass numbers A = 100, 106, 114, 116, 120, and 130 and in the chain of isotones with (N = 50) 88 Sr, 90 Zr, 92 Mo is performed within this framework.

Electric dipole response in208Pb within a new microscopic multiphonon approach

“…Going beyond QRPA is necessary since other excitation modes may contribute to the E1 transitions falling in the energy region of the PDR. The RTBA [17][18][19] is based on a modern version of the Landau-Migdal theory [20,21] and treats consistently the quasiparticle-phonon coupling by choosing selectively the two-phonon states to be coupled to the QRPA phonons. The QPM [22] relies on a separable Hamiltonian and is able to enlarge the phonon basis so as to include a selected fraction of three-phonon states.…”

Quasiparticle-vibration coupling effects on nuclear transitions of astrophysical interest

“…A precise expression of W(ω) is obtained in the framework of the relativistic nuclear field theory and can be found in Ref. [3].…”

“…The Sn region around N = 82 is particularly important for r-process studies as 132 Sn is a so-called "waiting-point" nucleus where neutron-capture and photodesintegration processes are in equilibrium and β − -decay favorably occurs. Here we calculated E1 modes and GT transitions in the (p,n) branch (GT − transitions) in a few Sn isotopes using the following numerical scheme: as a first step, the basis (k i τ , η i ) of single quasiparticles is obtained by performing a relativistic mean-field calculation using NL3 parametrization of the meson-exchange interaction [12,8] and monopole-monopole pairing force, as described in Reference [3], for which the HartreeBogoliubov approximation reduces to the Hartree+Bardeen-Cooper-Schrieffer (Hartree+BCS) one. The spectrum of collective phonons that are coupled to the quasiparticles are calculated within the RQRPA based on the same NL3 parameter set.…”

“…According to the formalism of the relativistic quasiparticle time-blocking approximation [3,5] we solve the Bethe-Salpeter equation (BSE) for the response function in the corresponding channels. In the like-particle case, the final BSE reads [3] …”

“…References [2,3,4,5]), to the description of various excitation modes of astrophysical interest. Based on the meson-nucleon Lagrangian of quantum hadrodynamics, the present approach starts from a covariant DFT description of the nucleus and uses Gorkov-Green function techniques and nuclear field theory to introduce correlations and compute the response of nuclei to various external fields.…”