Magnetic dipole excitations based on the relativistic nuclear energy density functional

Abstract

Magnetic dipole (M1) excitations build not only a fundamental mode of nucleonic transitions, but they are also relevant for nuclear astrophysics applications. We have established a theory framework for description of M1 transitions based on the relativistic nuclear energy density functional. For this purpose the relativistic quasiparticle random phase approximation (RQRPA) is established using density dependent point coupling interaction DD-PC1, supplemented with the isovectorpseudovector interaction channel in order to study unnatural parity transitions. The introduced framework has been validated using the M1 sum rule for core-plus-two-nucleon systems, and employed in studies of the spin, orbital, isoscalar and isovector M1 transition strengths in magic nuclei 48 Ca and 208 Pb, and open shell nuclei 42 Ca and 50 Ti. In these systems, the isovector spin-flip M1 transition is dominant, mainly between one or two spin-orbit partner states. It is shown that pairing correlations have a significant impact on the centroid energy and major peak position of the M1 mode. The M1 excitations could provide an additional constraint to improve nuclear energy density functionals in the future studies.I.

Nuclear magnetic transitions in the relativistic energy density functional approach

“…The relativistic quasiparticle random phase approximation (RQRPA) for description of M1 transition strength, based on relativistic point coupling interactions, was introduced in Ref. [21]. The nuclear ground state properties are described using the relativistic Hartree-Bogoliubov (RHB) model with DD-PC1 interaction, that provides singleparticle states and wave functions obtained in the canonical basis for the implementation in the RQRPA [21].…”

“…[21]. The nuclear ground state properties are described using the relativistic Hartree-Bogoliubov (RHB) model with DD-PC1 interaction, that provides singleparticle states and wave functions obtained in the canonical basis for the implementation in the RQRPA [21]. In addition to the point coupling interaction DD-PC1 used in the RHB model [21], for the description of unnatural parity excitations of the M1 type (J π = 1 + ), the RQRPA residual interaction is supplemented with the relativistic isovector-pseudovector contact interaction,…”

“…Since this term does not contribute to the ground state due to parity arguments, its strength parameter α IV−PV is constrained by the experimental data on M1 excitation energies of 48 Ca and 208 Pb [21]. By solving the RQRPA equations in the matrix formulation, the M1 transition strengths are obtained and further analyzed.…”

“…The M1 sum rule for core-plus-two-nucleon systems [25] has been used to validate the model calculations. The spin, orbital, isoscalar and isovector M1 transition strengths have been studied in detail in magic nuclei 48 Ca and 208 Pb, and open shell nuclei 42 Ca and 50 Ti [21]. In these systems, the isovector spin-flip M1 transition is dominant, mainly between one or two spin-orbit partner states.…”

“…Clearly, further theoretical studies of M1 transitions are required to resolve open questions on their properties. To respond to some of the open challenges, recently a novel theory framework has been established for studies of M1 excitations, based on the relativistic nuclear energy density functional [21,22]. This framework has been employed in several studies, including the analysis of basic M1 properties, their isotopic dependence and relationship with spinorbit interaction, the role of pairing properties, constraining the quenching of the g factors for the free nucleons, and others.…”