arXiv subjects

T. T. S. Kuo

Publications and source records attributed to T. T. S. Kuo.

At least 73 records · Page 4Linked to original sources

arXiv2000

Equivalence of model space techniques and the renormalization group for a separable model problem

Lee-Suzuki similarity transformations and Krencigowa-Kuo folded diagrams are two common methods used to derive energy independent model space effective interactions for nuclear many-body systems. We demonstrate that these methods are equivalent to a Renormalization Group (RG) analysis of a separable potential model. The effective low-momentum potentials V_{eff} are shown to give the same scaling equation that RG arguments predict. We find the new result that the different model space techniques considered in this paper yield a unique low-momentum V_{eff} when applied to the toy model problem.

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arXiv2000

Realistic Shell-Model Calculations for Proton-Rich N=50 Isotones

The structure of the N=50 isotones 98Cd, 97Ag, and 96Pd is studied in terms of shell model employing a realistic effective interaction derived from the Bonn-A nucleon-nucleon potential. The single-hole energies are fixed by resorting to an analysis of the low-energy spectra of the isotones with A>= 91. Comparison shows that our results are in very satisfactory agreement with the available experimental data. This supports confidence in the predictions of our calculations

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arXiv1999

Bonn Potential and Shell-Model Calculations for N=126 Isotones

We have performed shell-model calculations for the N=126 isotones 210Po, 211At, and 212Rn using a realistic effective interaction derived from the Bonn A nucleon-nucleon potential by means of a G-matrix folded-diagram method. The calculted binding energies, energy spectra and electromagnetic properties show remarkably good agreement with the experimental data. The results of this paper complement those of our previous study on neutron hole Pb isotopes, confirming that realistic effective interactions are now able to reproduce with quantitative accuracy the spectroscopic properties of complex nuclei.

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arXiv1998

Realistic Effective Intaractions and Nuclear Structure Calculations

We address the two main questions relevant to microscopic nuclear structure calculations starting from a free NN potential. These concern the accuracy of these kinds of calculations and the extent to which they depend on the potential used as input. Regarding the first question, we present some results obtained for nuclei around doubly magic 132Sn and 208Pb by making use of an effective interaction derived from the Bonn A potential. Comparison shows that our results are in very good agreement with the experimental data. As for the second question, we present the results obtained for the nucleus 134Te by making use of four different NN potentials. They indicate that nuclear structure calculations may help in understanding the off-shell nature of the NN potential.

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arXiv1998

Bonn Potential and Shell-Model Calculations for 206,205,204Pb

The structure of the nuclei 206,205,204Pb is studied interms of shell model employing a realistic effective interaction derived from the Bonn A nucleon-nucleon potential. The energy spectra, binding energies and electromagnetic properties are calculated and compared with experiment. A very good overall agreement is obtained. This evidences the reliability of our realistic effective interaction and encourages use of modern realistic potentials in shell-model calculations for heavy-mass nuclei.

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arXiv1998

Proton Particle-Neutron Hole States in 132Sb with a Realistic Interaction

The structure of the particle-hole nucleus 132Sb provides a direct source of information on the effective neutron-proton interaction in the 132Sn region. We have performed a shell-model calculation for this nucleus using a realistic effective interaction derived from the Bonn A nucleon-nucleon potential. The results are in very good agreement with the experimental data evidencing the reliability of our effective interaction matrix elements both with isospin T=1 and T=0.

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arXiv1997

Momentum Dependence of Single Particle Potential in Dirac Brueckner Approach

The momentum dependence of the empirical scalar and vector potentials needed for describing relativistic heavy-ion collisions at 1 GeV/nucleon is compared with that derived from self-consistent Dirac-Brueckner calculations using the Bonn-A potential. Our calculated scalar and vector potentials exhibit a weak momentum dependence and their magnitudes decrease with nucleon momentum, in close similarity with the momentum dependence required by the empirical potentials. The effects of explicit momentum dependence on the properties of equilibrium nuclear matter are found to be small.

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arXiv1997

Symmetry energy of nuclear matter and properties of neutron statrs in a relativistic approach

Asymmetric nuclear matter is treated in the formalism of Dirac-Brueckner approach with Bonn one-boson-exchange nucleon-nucleon interaction. We extract the symmetry energy coefficient at the saturation to be about 31 MeV, which is in good agreement with empirical value of $30\pm 4$ MeV. The symmetry energy is found to increase almost linearly with the density, which differs considerably from the results of non-relativistic approaches. This finding also supports the linear parameterization of Prakash, Ainsworth and Lattimer. We find, furthermore, that the higher-order dependence of the nuclear equation of state on the asymmetry parameter is unimportant up to densities relevant for neutron stars. The resulting equation of state of neutron-rich matter is used to calculate the maximum mass of neutron star, and we find it to be about 2.1$M_\odot$. Possible mechanisms for the softening of the equation of state are also discussed.

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arXiv1997

Suppression of core polarization in halo nuclei

We present a microscopic study of halo nuclei, starting from the Paris and Bonn potentials and employing a two-frequency shell model approach. It is found that the core-polarization effect is dramatically suppressed in such nuclei. Consequently the effective interaction for halo nucleons is almost entirely given by the bare G-matrix alone, which presently can be evaluated with a high degree of accuracy. The experimental pairing energies between the two halo neutrons in $^6$He and $^{11}$Li nuclei are satisfactorily reproduced by our calculation. It is suggested that the fundamental nucleon-nucleon interaction can be probed in a clearer and more direct way in halo nuclei than in ordinary nuclei.

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arXiv1997

Nuclear and Neutron Matter Calculations with Different Model Spaces

In this work we investigate the so-called model-space Brueckner-Hartree-Fock (MBHF) approach for nuclear matter as well as for neutron matter and the extension of this which includes the particle-particle and hole-hole (PPHH) diagrams. A central ingredient in the model-space approach for nuclear matter is the boundary momentum $k_M$ beyond which the single-particle potential energy is set equal to zero. This is also the boundary of the model space within which the PPHH diagrams are calculated. It has been rather uncertain which value should be used for $k_M$. We have carried out model-space nuclear matter and neutron matter calculations with and without PPHH diagrams for various choices of $k_M$ and using several modern nucleon-nucleon potentials. Our results exhibit a saturation region where the nuclear and neutron matter matter energies are quite stable as $k_M$ varies. The location of this region may serve to determine an "optimum" choice for $k_M$. However, we find that the strength of the tensor force has a significant influence on binding energy variation with $k_M$. The implications for nuclear and neutron matter calculations are discussed.

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arXiv1996

Isospin Lattice-Gas Model and Liquid-Gas Phase Transition in Asymmetric Nuclear Matter

An isospin lattice-gas model, which is a spin-1 Ising model, is employed to investigate the liquid-gas phase transition in asymmetric nuclear matter. We consider nuclear matter as a lattice where each lattice site can be either empty or occupied by a proton or a neutron, with a nearest-neighbor interaction among the nucleons. With the Bragg-Williams mean field approximation, we calculate various thermodynamic properties of nuclear matter for different densities and different proton-neutron asymmetry parameter $s$. Our model exhibits liquid-gas phase transition below a critical temperature $T_c$, and predicts a monotonic decreasing of $T_c$ as the magnitude of $s$ is increased. The dependence of the nuclear matter isotherms on the asymmetry parameter $s$ is discussed.

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arXiv1996

Non-collapsing quasiparticle random phase approximation for nuclear double-beta decay

We show how the longstanding problem of the collapse of the charge-exchange QRPA near the physical value of the force strength can be circumvented. This is done by including the effect of ground state correlations into the QRPA equations of motion. The corresponding formalism, called renormalized QRPA, is briefly outlined and its consequences are discussed in the framework of a schematic model for the two-neutrino double beta decay in the $^{100}Mo \rightarrow\, ^{100}Ru$ system. The question of the conservation of the Ikeda sum rule is also addressed within the new formalism.

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arXiv1996

Violation of the Ikeda sum rule and the self-consistency in the renormalized quasiparticle random phase approximation and the nuclear double-beta decay

The effect of the inclusion of ground state correlations into the QRPA equation of motion for the two-neutrino double beta ($ββ_{2ν}$) decay is carefully analyzed. The resulting model, called renormalized QRPA (RQRPA), does not collapse near the physical value of the nuclear force strength in the particle-particle channel, as happens with the ordinary QRPA. Still, the $ββ_{2ν}$ transition amplitude is only slightly less sensitive on this parameter in the RQRPA than that in the plain QRPA. It is argued that this fact reveals once more that the characteristic behaviour of the $ββ_{2ν}$ transition amplitude within the QRPA is not an artifact of the model, but a consequence of the partial restoration of the spin-isospin $SU(4)$ symmetry. It is shown that the price paid for bypassing the collapse in the RQRPA is the violation of the Ikeda sum rule.

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arXiv1996

Realistic effective interactions for halo nuclei

We study halo nuclei using a two-frequency shell-model approach employing wave functions of two different oscillator constants $\hbarω_{in}$ and $\hbarω_{out}$, the former for the inner orbits and the latter for the halo (outer) orbits. An initial application has been made for the halo nuclei $^6$He and $^6$Li, with $0s_{1/2}$ taken as the inner and ( $0p_{3/2}$, $0p_{1/2}$) as the halo orbits. Starting from the Paris NN interaction, we have derived a G-matrix folded-diagram effective interaction for this two-frequency model space, using an essentially exact treatment for the Pauli exclusion operator for the G-matrix. While keeping $\hbarω_{in}$ fixed, we have performed calculations with different choices for $\hbarω_{out}$, treating it as a variation parameter. For $\hbarω_{in}=19.7 MeV$ and $\hbarω_{out}=8.2 MeV$, our calculated valence energies for $^6$He and $^6$Li are -2.77 and -3.55 Mev, respectively, both in good agreement with experiments. The importance of certain three-body-force diagrams is discussed.

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arXiv1995

SMMC method for two-neutrino double beta decay

Shell Model Monte Carlo (SMMC) techniques are used to calculate two-neutrino double beta decay matrix elements. We validate the approach against direct diagonalization for $^{48}$Ca in the complete $pf$-shell using the KB3 interaction. The method is then applied to the decay of $^{76}$Ge in the $(0f_{5/2},1p,0g_{9/2})$ model space using a newly calculated realistic interaction. Our result for the matrix element is $0.13\pm0.05$ MeV$^{-1}$, in agreement with the experimental value.

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arXiv1995

Isospin Lattice Gas Model and Nuclear-Matter Phase Diagram and Pressure-Volume Isotherms

We study a cubic lattice gas model for nuclear matter where each lattice site can be either occupied, by one proton or one neutron, or unoccupied. A nearest-neighbor interaction of the form $ - \sum_{ } J_{ij}τ_{zi} τ_{zj}$ is assumed. Our model is an isospin-1 Ising model, with ${τ_z}$ = (1,0,-1) representing respectively (proton, vacancy, neutron). A kinetic-energy term has been included in our model. Under the Bragg-Williams mean field approximation our model exhibits the existence of a dense phase (liquid-like) and a rare phase (gas-like). The nuclear-matter p-v isotherms given by our model are discussed.

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arXiv1995

Nuclear Shell Model Calculations with Fundamental Nucleon-Nucleon Interactions

Some fundamental Nucleon-Nucleon interactions and their applications to finite nuclei are reviewed. Results for the few-body systems and from Shell-Model calculations are discussed and compared to point out the advantages and disadvantages of the different Nucleon-Nucleon interactions. The recently developed Drexel University Shell Model (DUSM) code is mentioned.

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arXiv1993

Projected Linear Response Theory for Charge-Exchange Excitations and Double Beta Decay

The projected random phase approximation (PRPA) for charge-exchange excitations is derived from the time-dependent variational principle. Explicit results for the unperturbed energies (including the self-energy corrections), the PRPA matrices, and the transition matrix elements are presented. The effect of the projection procedure on the two-neutrino $ββ$ decay in $^{76}Ge$ is briefly discussed.

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