SDPF-MU

SDPF-MU
Name	SDPF-MU
Type	effective interaction
Developers	Takaharu Otsuka; Noritaka Kaneko; Takaharu Suzuki; Michio Honma
Region	sd shell; pf shell
Nuclei	neutron-rich magnesium isotopes; silicon isotopes; sulfur isotopes; calcium isotopes
Introduced	2012
References	Otsuka et al. (2012)

SDPF-MU is a microscopic effective interaction designed for large-scale nuclear shell-model calculations spanning the sd and pf major shells. It was formulated to describe structural evolution in neutron-rich nuclei around the island of inversion and to incorporate novel tensor-force-driven monopole components. The interaction aims to reproduce spectroscopic properties across isotopic chains such as oxygen, neon, magnesium, silicon, and calcium nuclei while remaining consistent with ab initio insights from chiral effective field theory and empirical data from facilities like RIKEN and GANIL.

Introduction

SDPF-MU was developed to address anomalies in shell evolution observed in experiments at GANIL, RIKEN, MSU (now FRIB), and ISOLDE. The interaction combines monopole terms constrained by realistic two-body forces and tensor-force effects inferred from studies of Otsuka's tensor force and comparisons with interactions such as USD, SDPF-U, and GXPF1A. It responds to phenomena including the breakdown of the N=20 magic number in the island of inversion, the emergence of deformation in neon isotopes and magnesium isotopes, and spectroscopy of neutron-rich silicon and sulfur chains.

Development and Composition

SDPF-MU's construction merges microscopic and phenomenological elements: central and tensor monopole corrections were tuned using matrix elements derived from realistic interactions like CD-Bonn potential and constrained by chiral effective field theory calculations. The model space includes the sd-shell orbits (sd1/2, sd3/2, sd5/2 equivalents as for USD family) coupled to the pf-shell orbits (pf7/2, pf5/2, p3/2, p1/2 as in GXPF1A). Adjustments were made to single-particle energies to reproduce known levels in 16O, 40Ca, and neighboring nuclei such as 34Si and 48Ca. The tensor monopole components draw conceptual lineage from studies by Otsuka, Suzuki, Holt and relate to monopole migration phenomena seen in 18O and 42Si.

Applications in Nuclear Shell-Model Calculations

SDPF-MU has been applied to calculate excitation spectra, electromagnetic transition rates, and two-neutron separation energies for isotopic chains including neon, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, and heavier neighbors toward calcium and titanium. It has been used to interpret results from knockout experiments at Michigan State University, charge-exchange studies at RIKEN, and lifetime measurements at GANIL. Shell-model calculations using SDPF-MU reproduce the lowering of intruder configurations that characterize the island of inversion and can predict spectroscopic factors relevant to transfer reactions such as (d,p) and (p,2p) measured at TRIUMF and GSI.

Performance and Benchmarking

Benchmarking of SDPF-MU against experimental data shows improved reproduction of energy levels and transition probabilities compared with earlier sd-pf cross-shell interactions like SDPF-U and empirical pf interactions such as KB3G in specific neutron-rich regimes. Quantitative comparisons include root-mean-square deviations for low-lying states in 32Mg, 30Ne, 34Si, and 42Si and agreement with measured B(E2) values from Coulomb excitation at ISOLDE and lifetime data from NSCL. Calculations using SDPF-MU have been validated against ab initio coupled-cluster and in-medium similarity renormalization group results for light-to-medium mass nuclei including 22O and 48Ca, demonstrating consistency in predicted shell gaps and spectroscopic trends.

Extensions and Modifications

Following its introduction, SDPF-MU has been modified to incorporate updated monopole corrections, refined single-particle energies, and extensions to allow larger cross-shell excitations for studies of shape coexistence in nuclei such as 44S and 40Mg. Variants have explored coupling to continuum effects relevant for dripline systems studied at RIBF and inclusion of three-nucleon force inspired shifts connected to chiral EFT three-body terms. Hybrid approaches combine SDPF-MU with interactions like GXPF1A for heavier pf-dominant systems and with microscopic effective interactions renormalized via Vlow-k or SRG techniques to improve convergence.

Impact and Reception in Nuclear Physics

SDPF-MU has been influential in reshaping interpretations of shell evolution and magicity in exotic nuclei, cited in experimental analyses from GANIL, RIKEN, MSU/FRIB, GSI, ISOLDE, TRIUMF, and theoretical overviews in journals such as Physical Review Letters and Physical Review C. Its emphasis on tensor-driven monopole migration has spurred complementary theoretical work on tensor forces by researchers affiliated with institutions including RCNP, RIKEN, University of Tokyo, and Michigan State University. The interaction remains a standard tool in shell-model studies of the sd-pf region and continues to inform the design and interpretation of experiments at next-generation facilities like FRIB and RIBF.

Category:Nuclear shell model interactions