arXiv subjects

Masayuki Matsuo

Publications and source records attributed to Masayuki Matsuo.

46 records · Page 3Linked to original sources

arXiv2008

Deformation around neutron-rich Cr isotopes in axially symmetric Skyrme-Hatree-Fock-Bogoliubov method

We analyse deformation mechanism in neutron-rich Cr, Fe and Ti isotopes with N=32-44 by means of a Skyrme-Hartree-Fock-Bogoliubov mean-field code employing a two-dimensional mesh representation in the cylindrical coordinate system. Evaluating systematically the quadrupole deformation energy, we show that the Skyrme parameter set SkM* gives a quadrupole instability around the neutron number N$\sim$38-42 in Cr isotopes, where the deformation energy curve suggests a transitional behavior with a shallow minimum extending to a large prolate deformation. Roles of a deformed N=38 gap and the position of the neutron g9/2 orbit are analysed in detail.

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arXiv2007

Microscopic Derivation of Collective Hamiltonian by Means of the Adiabatic Self-Consistent Collective Coordinate Method

Microscopic dynamics of the oblate-prolate shape coexistence/mixing phenomena in 68Se and 72Kr are studied by means of the adiabatic self-consistent collective coordinate (ASCC) method in conjunction with the pairing-plus-quadrupole (P+Q) Hamiltonian including the quadrupole pairing interaction. Quantum collective Hamiltonian is constructed, and excitation spectra, spectroscopic quadrupole moments and quadrupole transition properties are evaluated. The effect of the time-odd pair field on the collective mass (inertia function) of the large-amplitude vibration and the rotational moments of inertia about three principal axes is evaluated. Basic properties of the shape coexistence/mixing are well reproduced. The calculation indicates that the oblate-prolate shape mixing decreases as the angular momentum increases.

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arXiv2007

Microscopic Dynamics of Shape Coexistence Phenomena around 68Se and 72Kr

The adiabatic self-consistent collective coordinate (ASCC) method is applied to the pairing-plus-quadrupole (P + Q) model Hamiltonian including the quadrupole pairing, and the oblate-prolate shape coexistence phenomena in proton-rich nuclei, 68Se and 72Kr, are investigated. It is shown that the collective path connecting the oblate and prolate local minima runs along a triaxial valley in the beta-gamma plane. Quantum collective Hamiltonian is constructed and low-lying energy spectra and E2 transition probabilities are calculated for the first time using the ASCC method. Basic properties of the shape coexistence/mixing are well reproduced. We also clarify the effects of the time-odd pair field on the collective mass (inertial function) for the large-amplitude vibration and on the rotational moments of inertia about three principal axes.

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arXiv2007

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.

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arXiv2006

Spatial structure of neutron Cooper pair in low density uniform matter

We analyze spatial structure of the neutron Cooper pair in superfluid low-density uniform matter by means of BCS calculations employing a bare force and the effective Gogny interaction. It is shown that the Cooper pair exhibits a strong spatial di-neutron correlation in a wide range of neutron density $ρ/ρ_0\approx 10^{-4}-0.5$. This feature is related to the crossover behavior between the pairing of the weak coupling BCS type and the Bose-Einstein condensation of bound neutron pairs. We also show that the zero-range delta interaction can describe the spatial structure of the neutron Cooper pair if the density dependent interaction strength and the cut-off energy are appropriately chosen. Parameterizations of the density-dependent delta interaction satisfying this condition are discussed.

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arXiv2005

Effects of Time-Odd Components in Mean Field on Large Amplitude Collective Dynamics

We apply the adiabatic self-consistent collective coordinate (ASCC) method to the multi-O(4) model and study collective mass (inertia function) of the many-body tunneling motion. Comparing results with those of the exact diagonalization, we show that the ASCC method succeeds in describing gradual change of excitation spectra from an anharmonic vibration about the spherical shape to a doublet pattern associated with a deformed double-well potential possessing the oblate-prolate symmetry. The collective mass is significantly increased by the quadrupole-pairing contribution to time-odd components of the moving mean field. In contrast, the cranking (Inglis-Belyaev) mass based on the constrained mean field, which ignores the time-odd components, is smaller than the ASCC mass and fails to reproduce the exact spectra.

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arXiv2004

Di-neutron correlation and soft dipole excitation in medium mass neutron-rich nuclei near drip-line

The neutron pairing correlation and the soft dipole excitation in medium-mass nuclei near drip-line are investigated from a viewpoint of the di-neutron correlation. Numerical analyses by means of the coordinate-space HFB and the continuum QRPA methods are performed for even-even $^{18-24}$O, $^{50-58}$Ca and $^{80-86}$Ni. A clear signature of the di-neutron correlation is found in the HFB ground state; two neutrons are correlated at short relative distances $\lesim 2$ fm with large probability $\sim 50%$. The soft dipole excitation is influenced strongly by the neutron pairing correlation, and it accompanies a large transition density for pair motion of neutrons. This behavior originates from a coherent superposition of two-quasiparticle configurations $[l\times (l+1)]_{L=1}$ consisting of continuum states with high orbital angular momenta $l$ reaching an order of $l\sim 10$. It raises a picture that the soft dipole excitation under the influence of neutron pairing is characterized by motion of di-neutron in the nuclear exterior against the remaining $A-2$ subsystem. Sensitivity to the density dependence of effective pair force is discussed.

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arXiv2003

Fluctuation properties of strength functions associated with giant resonances

We performed fluctuation analysis by means of the local scaling dimension for the strength function of the isoscalar (IS) and the isovector (IV) giant quadrupole resonances (GQR) in $^{40}$Ca, where the strength functions are obtained by the shell model calculation within up to the 2p2h configurations. It is found that at small energy scale, fluctuation of the strength function almost obeys the Gaussian orthogonal ensemble (GOE) random matrix theory limit. On the other hand, we found a deviation from the GOE limit at the intermediate energy scale about 1.7MeV for the IS and at 0.9MeV for the IV. The results imply that different types of fluctuations coexist at different energy scales. Detailed analysis strongly suggests that GOE fluctuation at small energy scale is due to the complicated nature of 2p2h states and that fluctuation at the intermediate energy scale is associated with the spreading width of the Tamm-Dancoff 1p1h states.

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arXiv2002

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.

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arXiv1999

Scaling Analysis of Fluctuating Strength Function

We propose a new method to analyze fluctuations in the strength function phenomena in highly excited nuclei. Extending the method of multifractal analysis to the cases where the strength fluctuations do not obey power scaling laws, we introduce a new measure of fluctuation, called the local scaling dimension, which characterizes scaling behavior of the strength fluctuation as a function of energy bin width subdividing the strength function. We discuss properties of the new measure by applying it to a model system which simulates the doorway damping mechanism of giant resonances. It is found that the local scaling dimension characterizes well fluctuations and their energy scales of fine structures in the strength function associated with the damped collective motions.

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