arXiv subjects

R. Okamoto

Publications and source records attributed to R. Okamoto.

25 records · Page 2Linked to original sources

arXiv2003

Charge-dependent calculations of single-particle energies in nuclei around ^{16}O with modern nucleon-nucleon interactions

The binding energies of the ground states and several excited states related to single-particle and -hole states in nuclei around ^{16}O are calculated taking charge dependence into account. Effective interactions on the particle basis are constructed from modern charge-dependent nucleon-nucleon interactions and the Coulomb force within the framework of the unitary-model-operator approach. Single-particle (-hole) energies are obtained from the energy differences of the binding energies between a particle (hole) state in ^{17}O or ^{17}F (^{15}N or ^{15}O) and the ground state of ^{16}O. The resultant spin-orbit splittings are small for the hole state and large for the particle state in comparison with the experimental values though the differences between the experimental and calculated values are not very large. The charge dependence of the calculated single-particle energies for the ground states are in good agreement with the experimental values. Furthermore, the Thomas-Ehrman shift due to the Coulomb force for the 1s_{1/2} states in ^{17}O and ^{17}F can be observed.

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arXiv2002

Shell-Model Calculations for_Λ^{16}O and_Λ^{17}O Using Microscopic Effective Interactions with ΣDegrees of Freedom

Shell-model calculations in a large model space are performed for _Λ^{16}O and_Λ^{17}O. Effective interactions with degrees of freedom of Σin addition to Λand nucleons are derived from hyperon-nucleon and nucleon-nucleon interactions within the framework of the unitary-model-operator approach. Effects of the Σdegrees of freedom and the parity-mixing intershell coupling on the Λhypernuclear structure are investigated, employing the Nijmegen NSC97a-f and NSC89 hyperon-nucleon potentials.

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arXiv2000

Three-Body-Cluster Effects on Lambda Single-Particle Energies in _{Lambda}^{17}O and_{Lambda}^{41}Ca

A method for a microscopic description of Lambda hypernuclei is formulated in the framework of the unitary-model-operator approach. A unitarily transformed hamiltonian is introduced and given in a cluster expansion form. The structure of three-body-cluster terms are discussed especially on the Lambda single-particle energy. The Lambda single-particle energies including the three-body-cluster contributions are calculated for the 0s_{1/2}, 0p_{3/2} and 0p_{1/2} states in_{Lambda}^{17}O, and for the 0s_{1/2}, 0p_{3/2}, 0p_{1/2}, 0d_{5/2}, 0d_{3/2} and 1s_{1/2} states in_{Lambda}^{41}Ca, using the Nijmegen soft-core (NSC), NSC97a-f, the Juelich A (J A) and J B hyperon-nucleon interactions. It is indicated that the three-body-cluster terms bring about sizable effects in the magnitudes of the Lambda single-particle energies, but hardly affect the Lambda spin-orbit splittings.

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arXiv1999

Exact Treatment of the Pauli Exclusion Operator in Nuclear Matter Calculation

Exact expressions of the Pauli exclusion operator Q in the nuclear matter calculation are presented in detail. Exact formulae are also given for the calculations of the single-particle-potential energy and the binding energy per nucleon with the exact Q operator. Numerical calculations of the G matrix in the lowest-order Brueckner theory are carried out to check the reliability of the standard angle-average approximation for the Q operator by employing the Bonn B and C NN potentials. It is observed that the exact treatment of the operator Q brings about non-negligible and attractive contributions to the binding energy.

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arXiv1999

Unitary-model-operator approach to $Λ$ hypernuclei

A method is formulated for the description of lambda hypernuclei in the framework of the unitary-model-operator approach (UMOA). The method is applied to $_Λ^{17}$O. A lambda-nucleon effective interaction is derived, taking the coupling of the sigma-nucleon channel into account. The lambda single-particle energies are calculated for the 0s_{1/2}, 0p_{3/2} and 0p_{1/2} states employing the Nijmegen soft-core (NSC), Jülich model-Ã (JÃ) and model-B (JB) hyperon-nucleon potentials.

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arXiv1993

Approximate Treatment of Hermitian Effective Interactions and a Bound on the Error

The Hermitian effective interaction can be well-approximated by (R+R^dagger)/2 if the eigenvalues of omega^dagger omega are small or state-independent(degenerate), where R is the standard non-Hermitian effective interaction and omega maps the model-space states onto the excluded space. An error bound on this approximation is given.

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arXiv1993

Iterative Solution for Effective Interactions in a System with Non-degenerate Unperturbed Energies

We generalize the Lee-Suzuki iteration method for summing the folded diagram series to the case where the unperturbed model-space energies are non-degenerate. A condition is derived for the convergence of the iteration scheme and this depends on the choice of the model space projection operators. Two choices are examined, in the first the projection operators are defined in terms of the unperturbed states and in the second they are defined in terms of the eigenfunctions obtained at each stage of the iteration. As is illustrated by calculations with a simple model, the second procedure gives the better convergence and, by suitable choice of the starting energies, allows the reproduction of any subset of the exact eigenvalues.

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