518 research outputs found
Spatial structure of Cooper pairs in nuclei
We discuss the spatial structure of the Cooper pair in dilute neutron matter
and neutron-rich nuclei by means of the BCS theory and the
Skyrme-Hartree-Fock-Bogioliubov model, respectively. The neutron pairing in
dilute neutron matter is close to the region of the BCS-BEC crossover in a wide
density range, giving rise to spatially compact Cooper pair whose size is
smaller than the average interaparticle distance. This behavior extends to
moderate low density ( of the saturation density) where the
Cooper pair size becomes smallerst ( fm). The Cooper pair in finite
nuclei also exhibits the spatial correlation favoring the coupling of neutrons
at small relative distances r \lesim 3 fm with large probability.
Neutron-rich nuclei having small neutron separation energy may provide us
opportunity to probe the spatial correlation since the neutron pairing and the
spatial correlation persists also in an area of low-density neutron
distribution extending from the surface to far outside the nucleus.Comment: 13 pages, 5 figures, chapter in "Fifty Years of Nuclear BCS", eds.
R.A. Broglia and V.Zelevinsk
Collective Excitations and Pairing Effects in Drip-Line Nuclei -- Continuum RPA in Coordinate-Space HFB --
We discuss novel features of a new continuum RPA formulated in the
coordinate-space Hartree-Fock-Bogoliubov framework. This continuum
quasiparticle RPA takes into account both the one- and two-particle escaping
channels. The theory is tested with numerical calculations for monopole, dipole
and quadrupole excitations in neutron-rich oxygen isotopes near the drip-line.
Effects of the particle-particle RPA correlation caused by the pairing
interaction are discussed in detail, and importance of the selfconsistent
treatment is emphasized.Comment: PTPTeX, 10 pages, 8 figures, talk at the Yukawa International Seminar
2001 (YKIS01) on "Physics of Unstable Nuclei", November 5-10, 2001, Kyoto,
Japa
Continuum Coupling and Pair Correlation in Weakly Bound Deformed Nuclei
We formulate a new Hartree-Fock-Bogoliubov method applicable to weakly bound
deformed nuclei using the coordinate-space Green's function technique. An
emphasis is put on treatment of quasiparticle states in the continuum, on which
we impose the correct boundary condition of the asymptotic out-going wave. We
illustrate this method with numerical examples.Comment: 5 pages, 4 figures, Proceedings of the Japanese French Symposium -
New paradigms in Nuclear Physics, Paris, 29th September - 2nd October, to be
published in Int. J. of Modern Physics
Gauge-Invariant Formulation of Adiabatic Self-Consistent Collective Coordinate Method
The adiabatic self-consistent collective coordinate (ASCC) method is a
practical microscopic theory of large-amplitude collective motions in nuclei
with superfluidity. We show that its basic equations are invariant against
transformations involving the gauge angle in the particle-number space. By
virtue of this invariance, a clean separation between the large-amplitude
collective motion and the pairing rotational motion can be achieved, enabling
us to restore the particle-number symmetry broken by the
Hartree-Fock-Bogoliubov (HFB) approximation. We formulate the ASCC method
explicitly in a gauge-invariant form. In solving the ASCC equations, it is
necessary to fix the gauge. Applying this new formulation to the multi-O(4)
model, we compare different gauge-fixing procedures and demonstrate that
calculations using different gauges indeed yield the same results for
gauge-invariant quantities, such as the collective path and quantum spectra. We
suggest a gauge-fixing prescription that seems most convenient in realistic
calculations.Comment: 27 pages, 7 figures, submitted to Prog. Theor. Phy
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