Isovector spin-singlet (T=1, S=0) and isoscalar spin-triplet (T=0, S=1) pairing interactions and spin-isospin response

Abstract

We review several experimental and theoretical advances that emphasise common aspects of the study of T=1 and T=0 pairing correlations in nuclei. We first discuss several empirical evidences of the special role played by the T=1 pairing interaction. In particular, we show the peculiar features of the nuclear pairing interaction in the low density regime, and possible outcomes such as the BCS-BEC crossover in nuclear matter and, in an analogous way, in loosely bound nuclei. We then move to the competition between T=1 and T=0 pairing correlations. The effect of such competition on the low-lying spectra is studied in N=Z odd-odd nuclei by using a three-body model; it is shown that the inversion of the 0+ and 1+ states near the ground state, and the strong magnetic dipole transitions between them, can be considered as a clear manifestation of strong T=0 pairing correlations in these nuclei. The effect of T=0 pairing correlations is also quite evident if one studies charge-changing transitions. The Gamow-Teller (GT) states in N=Z+2 nuclei are studied here by using self-consistent HFB+QRPA calculations in which the T=0 pairing interaction is taken into account. Strong GT states are found, near the ground state of daughter nuclei; these are compared with available experimental data from charge-exchange reactions, and such comparison can pinpoint the value of the strength of the T=0 interaction. Pair transfer reactions are eventually discussed: while two-neutron transfer has been long proposed as a tool to measure the T=1 superfluidity in the nuclear ground states, the study of deuteron transfer is still in its infancy, despite its potential interest in revealing effects coming from both T=1 and T=0 interactions.

Paper submitted to Physica Scripta for inclusion in the Focus Issue entitled "Focus Issue on Nuclear Structure: Celebrating the 75 Nobel Prize" (by A. Bohr and B.R. Mottelson). arXiv admin note: text overlap with arXiv:nucl-th/0512021 by other authors

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• Comparative study on charge radii and their kinks at magic numbers
• Stellar electron capture rates based on finite temperature relativistic quasiparticle random-phase approximation
• Isovector and isoscalar proton-neutron pairing in $N>Z$ nuclei
• Medium polarization effects in 3SD1 spin-triplet pairing
• Quartetting in odd-odd self-conjugate nuclei
• Finite-temperature linear response theory based on relativistic Hartree Bogoliubov model with point-coupling interaction
• Effect of isoscalar spin-triplet pairings on spin-isospin responses in $sd-$ shell nuclei
• Neutron-proton pairing in Nuclear Matter
• Consistent description for cluster dynamics and single-particle correlation
• Isoscalar and Isovector spin response in $sd-$ shell nuclei
• Empirical pairing gaps and neutron-proton correlations
• Band-like structures and quartets in deformed N=Z nuclei
• Pairing correlations and eigenvalues of two-body density matrix in atomic nuclei
• Effects of pairing correlations on the neutron skin thickness and the symmetry energy
• Spin-Triplet Pairing in Heavy Nuclei is Stable Against Deformation
• Triplet-odd pairing in finite nuclear systems: Even-even singly closed nuclei
• Isovector spin susceptibility: Isotopic evolution of collectivity in spin response
• Isovector pair correlations in analytically solvable models
• Proton-neutron pairing and binding energies of nuclei close to N=Z line
• Coexistence of isospin I = 0 and I = 1 pairings in asymmetric nuclear matter
• Nuclear Pairing Energy vs Mean Field Energy: Do They Talk To Each Other For Searching The Energy Minimum?