arXiv subjects

Tomohiro Oishi

Publications and source records attributed to Tomohiro Oishi.

At least 19 recordsLinked to original sources

arXiv2026

Mass radius and D-term of atomic nuclei in relativistic mean field theory

Based on relativistic mean field theory for atomic nuclei, we compute the mass radius and other radii associated with the energy momentum tensor for dozens of spin-0 nuclei across the nuclear chart. We also compute the D-term of these nuclei, the forward limit of the gravitational form factor $D(t=0)=D$. The dependence on the neutron number $N$ is systematically studied for calcium (Ca), nickel (Ni), zirconium (Zr), tin (Sn) and lead (Pb) isotopes. Remarkably, $|D|$ does not monotonically increase with $N$. Instead, it exhibits local maxima and minima when $N$ equals a magic number and even a sub-magic number. This results in characteristic kinks in the mass, scalar, tensor and shear radii of these isotopes. Our work for the first time elucidates the strong sensitivity of the various mechanical properties of nuclei to the nuclear shell structure.

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arXiv2026

Two-proton emission as source of spin-entangled proton pairs

We show that a two-proton emitter with a diproton-correlated initial state can act as a source of spin-correlated proton pairs. Using a time-dependent three-body model, we investigate the two-proton emission of $^{16}$Ne ($^{14}$O$+2p$) and analyze the spin correlation of the emitted protons. We find that, when the emission proceeds as a democratic three-body process from an initial state containing a spin-singlet diproton correlation, the emitted protons exhibit a pronounced spin-correlation pattern exceeding the local-hidden-variable bound. This spin correlation closely resembles that of a pure spin-singlet pair. In contrast, this pattern is lost when the process is dominated by the sequential emission or when the initial diproton correlation is absent. These results demonstrate that a certain class of two-proton emitters can deliver spin-entangled proton pairs, and their spin correlation reflects the diproton correlation embedded in the initial state.

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arXiv2025

Spin correlation in two-proton emission from $^6$Be

This paper presents a theoretical evaluation of spin correlation in the two-proton ($2p$) radioactive emission. The three-body model of $^{6}$Be with the proton-proton interaction, which is adjusted to reproduce the experimental energy release, is utilized. Time-dependent calculation is performed to compute the coupled-spin state of the emitted two protons. The spin-correlation function $S$ as the Clauser-Horne-Shimony-Holt (CHSH) indicator is evaluated as $|S| \cong 2.65$. Namely, the $2p$-spin correlation beyond the limit of local-hidden-variable (LHV) theory is suggested. This correlation is sensitive to the proton-proton interaction. The short-lived (broad-width) $2p$~state has the weaker spin correlation. In parallel, the core-proton interactions do not harm this correlation during the time-dependent decaying process. The CHSH measurement can be a novel probe into the effective nuclear interaction inside finite systems. Two-proton emitters can provide a testing field for identical-particle entanglement.

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arXiv2025

One-proton emission of $^{102}$Sb and its sensitivity to proton-neutron interaction

One-proton emission from the $^{102}$Sb nucleus is discussed, assuming an inert $^{100}$Sn core and the valence proton and neutron. There are experimentally measured bound states in the $^{100}$Sn-neutron system, whereas no particle-bound $^{100}$Sn-proton state has been observed. With time-dependent three-body calculations, the $1^+$ ground state of $^{102}$Sb is suggested as a possible proton emitter. This conclusion is reached by assuming a weakening effect on the proton-neutron ($pn$) interaction with respect to a bare deuteron. An analogous phenomenon is necessary to reproduce the empirical binding energies of $^{42}$Sc and $^{18}$F. Continuous shift from the unbound to bound regions by changing the $pn$-interaction strength is demonstrated. The lower limit of lifetime is evaluated as $τ\gtrsim 4.4 \times 10^{-18}$ seconds in the no-$pn$-interaction limit. However, the actual lifetime is expected as longer with a finite $pn$ interaction. Observation of a resonant state in $^{102}$Sb and its decay would provide a benchmark of the $pn$-pairing correlation.

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arXiv2025

Analytic continuation in coupling constant applied to two-proton emitters

For quantum meta-stable problems with three particles, the $^{6}$Be and $^{16}$Ne nuclei as two-proton ($2p$) emitters provide a testing field. Considering the complexity of many-body meta-stable systems, a tractable solver has been on demand. We apply the analytic continuation in coupling constant (ACCC) to these nuclei, and confirm that this method can solve such problems consistently to the time-dependent results as well as to the experimental data. The sensitivity of the $2p$ energies and widths to the proton-proton interaction is also investigated. The $^{6}$Be shows a smooth shift from short-life to long-life systems according to the proton-proton interaction. Same is concluded for the $2^+$ resonance of $^{16}$Ne. In contrast, for the first and second $0^+$ resonances of $^{16}$Ne, their energies and widths show the avoid-crossing behaviour, due to the coupling of two configurations in the core-proton subsystem, $^{15}$F. Since it requires only the bound-state solvers, the ACCC can be a low-cost option to solve three or more-body resonances.

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arXiv2024

Interference of resonances in two-proton emission of $^{16}$Ne

We investigate the two-proton ($2p$) emission from $^{16}$Ne with the time-dependent $^{14}$O$+p+p$ three-body calculations. Two $0^+$ resonances are suggested to participate. For the $0^+_1$ resonance, the true emission of the spatially localized two protons is dominant, if the single-particle $s_{1/2}$ resonance locates above the $2p$ energy. By evaluating a time-evolution probability, the $0^+_2$ resonance is suggested at $\cong 3$ MeV from the $2p$ threshold. The inclusion of $0^+_2$ resonance makes the true-$2p$~emission more dominant in the time-dependent calculations.

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arXiv2024

Triplet-odd pairing in finite nuclear systems: Even-even singly closed nuclei

Background: The appearance of the pairing condensate is an essential feature of many-fermion systems. There are two possible types of pairing: spin-singlet and spin-triplet. However, an open question remains as to whether the spin-triplet pairing condensate emerges in finite nuclei. Purpose: The aim of this work is to examine the coexistence of the spin-singlet and spin-triplet like-particle pairing condensates in nuclei. We also discuss the dependence on the type of pairing functional. Method: The Hartree-Fock-Bogoliubov calculations with a Skyrme $+$ local-pair energy-density functional (EDF) are performed to investigate the pairing condensate in the spherical ground states of Ca and Sn isotopes. Results: The spin-singlet pair EDF induces not only the spin-singlet but also the spin-triplet pairing condensates due to a strong spin-orbit splitting. By discarding the spin-orbit EDF, only the spin-singlet pairing condensate appears. The spin-triplet pair EDF, however, induces the spin-orbit splitting and accordingly the spin-singlet pairing condensate. Conclusions: The spin-orbit splitting plays an essential role in the coexistence of the spin-singlet and spin-triplet pairing condensates in nuclei.

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arXiv2023

Comparative study on charge radii and their kinks at magic numbers

Isotope dependences of charge radii, i.e., isotope shifts, calculated by the Skyrme Hartree-Fock, the relativistic mean-field, and the relativistic Hartree-Fock calculations are compared against the experimental data of magic and semimagic nuclei. It is found that the tensor interaction plays a role in reproducing the ``kink'' behavior, irregularity of isotope shifts at the neutron magic number, in the relativistic Hartree-Fock approach. With several Skyrme models, it is found that the kink behavior can be reproduced with the spin-orbit interaction having nonzero isovector channel. The single-particle orbitals near the Fermi energy are crucial to determine the kink size. The effects of the symmetry energy and the pairing interaction are also discussed in relation to the kink behavior.

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arXiv2023

Instruction of my personal computing library

This document is prepared to introduce and explain how to use the computing library composed by T. Oishi. The library-01 TOSPEM solves, for the spherical nucleus, (i) the Schroedinger equation for the single-nucleon states within the Woods-Saxon potential, (ii-a) the electric or magnetic transition strength, B(EJ) or B(MJ), between the arbitrary set of initial and final states of the nucleus of interest, and (ii-b) Weisskopf estimate for comparison with results in (ii-a). The library-02 RESONA is composed to solve the resonant eigenstates of spherical Schroedinger equations. The final version is expected to be published for educational and commercial purposes. Before the official publication, under the agreement with publishers, I make the current, preliminary version open for public. Two applications, GFORTRAN and GNUPLOT, are necessary for full usage. Feedbacks and comments on products will be appreciated. The source codes etc. are available in the GitHub repository [1].

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arXiv2023

Diproton correlation and two-proton emission from proton-rich nuclei

Open-print version of dissertation thesis. This thesis focuses on the relation between the diproton correlation and the two-proton emission with quantum entanglement. For this purpose, I developed a time-dependent three-body (proton-proton-core) model, where one Cooper pair of protons move inside the mean-field potential. The time-dependent calculation based on the three-body model provides an intuitive way to describe the quantum dynamics of the entangled fermionic pair. It has been shown that, by considering the Cooper-pairing correlation in the initial state of the two protons, (i) the experimental 2p-decay width of Be-6 is well reproduced, and (ii) the two protons are emitted mainly as a diproton-like cluster with the spin-singlet configuration in the early stage of the emission. Hence, the two-proton emission can provide an access to the diproton correlation. This thesis presented the first step to theoretically investigate the diproton correlation as well as quantum entanglement in the time-dependent radioactive emission. [NOTE] In this open-print version, several Figures were inevitably eliminated, because of the copyright and/or file-size problems. Several minor corrections have been done, but without changing the scientific discussions, results, and conclusions from the original version in 2014.

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arXiv2023

Time-dependent Dirac equation applied to one-proton radioactive emission

Relativistic energy-density functional (REDF) theory has been developed and utilized for self-consistent meanfield calculations of atomic nuclei. The proton-emitting radioactivity can provide a suitable reference to improve the predicting ability of REDF especially on the proton-drip line. One needs to consider the quantum tunneling effect, which plays an essential role in nucleon-emitting radioactive processes. However, the relativistic quantum tunneling has been less investigated compared with the non-relativistic case. This work is devoted to a theoretical evaluation of one-proton ($1p$) radioactivity based on the relativistic Dirac formalism. For this purpose, I develop the time-dependent (TD) Dirac-spinor calculation to simulate the $1p$ emission. By utilizing the relativistic Hartree-Bogoliubov (RHB) calculation with the DD-PCX parameters, single-proton potentials for the time-dependent Dirac spinor are determined. The TD-Dirac calculation is applied to the $1p$ emissions from the $^{37}$Sc and $^{39}$Sc nuclei, which can be well approximated as the valence proton and the proton-close-shell cores. The sensitivity of $1p$-emission energy and decaying width to the mass number is demonstrated. Remarkable sensitivity exists due to the size of system, which affects the nuclear part of potentials and energy levels, whereas the Coulomb barrier is common with the same atomic number. The calculated $1p$ energy and decaying lifetime are roughly consistent to the experimental limitation. The present TD-Dirac calculation is expected as applicable widely to proton-rich nuclides in order to improve the REDF by utilizing the $1p$-emission data.

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arXiv2022

Symmetry breaking of Gamow-Teller and magnetic-dipole transitions and its restoration in calcium isotopes

Nuclear magnetic-dipole (M1) and Gamow-Teller (GT) transitions provide insight into the spin-isospin properties of atomic nuclei. By considering them as unified spin-isospin transitions, the M1/GT transition strengths and excitation energies are subject to isospin symmetry. The excitation properties associated to the M1/GT symmetry need to be clarified within consistent theoretical approach. In this work, the relationship between the M1 and GT transitions in Ca isotopes is investigated in a unified framework based on the relativistic energy-density functional (REDF) with point-coupling interactions, using the relativistic quasi-particle random-phase approximation (RQRPA). It is shown that the isovector-pseudovector (IV-PV) residual interaction affects both transitions, and the symmetry of M1 and giant-GT transitions is disrupted by this interaction in closed-shell nuclei. In open-shell Ca isotopes, the proton-neutron pairing in the residual RQRPA interaction also plays a role in GT transitions. Due to the interplay between these interactions, the M1/GT symmetry can be restored especially in the $^{42}$Ca nucleus, i.e., the giant-GT strength can become comparable to that of the M1 mode in terms of the unified spin-isospin transitions by adjusting the PN-pairing strength to reproduce the experimental low-lying GT-excitation energies. The mirror symmetry of both M1 and GT transitions is also demonstrated for open-shell mirror partners, $^{42}$Ca and $^{42}$Ti. Further improvements are required to achieve simultaneous reproduction of M1 and GT-transition energies in the REDF framework.

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arXiv2021

Discerning nuclear pairing properties from magnetic dipole excitation

Pairing correlation of Cooper pair is a fundamental property of multi-fermion interacting systems. For nucleons, two modes of the Cooper-pair coupling may exist, namely of $S_{12}=0$ with $L_{12}=0$ (spin-singlet s-wave) and $S_{12}=1$ with $L_{12}=1$ (spin-triplet p-wave). In nuclear physics, it has been an open question whether the spin-singlet or spin-triplet coupling is dominant, as well as how to measure their role. We investigate a relation between the magnetic-dipole (M1) excitation of nuclei and the pairing modes within the framework of relativistic nuclear energy-density functional (RNEDF). The pairing correlations are taken into account by the relativistic Hartree-Bogoliubov (RHB) model in the ground state, and the relativistic quasi-particle random-phase approximation (RQRPA) is employed to describe M1 transitions. We have shown that M1 excitation properties display a sensitivity on the pairing model involved in the calculations. The systematic evaluation of M1 transitions together with the accurate experimental data enables us to discern the pairing properties in finite nuclei.

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arXiv2020

Role of residual interaction in the relativistic description of M1 excitation

Magnetic dipole (M1) excitation is the leading mode of multi-nucleon excitations induced by the magnetic field, and is a phenomenon of the spin-orbit (SO) splitting and residual interactions involved. In this work, we investigate the effects of the residual interactions on the M1 excitation from a novel perspective, the framework of relativistic nuclear energy-density functional (RNEDF). The relativistic Hartree-Bogoliubov (RHB) model is utilized to determine the nuclear ground state properties, while the relativistic quasi-particle random-phase approximation (RQRPA) is employed for the description of M1-excitation properties. From the analysis of M1 mode in the Ca isotope chain, role of the isovector-pseudovector (IV-PV) residual interaction is discussed. For open-shell nuclei, the pairing correlation also plays a noticeable role in the M1 mode. The experimental data on M1 mode is expected to provide a suitable reference to improve and optimize the theoretical aspects to describe the residual interactions.

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arXiv2019

Relativistic energy-density functional approach to magnetic-dipole excitation and its sum rule

Magnetic-dipole (M1) excitations of $^{18}$O and $^{42}$Ca nuclei are investigated within a relativistic nuclear energy density functional framework. In our last work \cite{2019OP}, these nuclei are found to have unique M1 excitation and its sum rule, because of their characteristic structure: the system consists of the shell-closure core plus two neutrons. For a more systematic investigation of the M1 mode, we have implemented a framework based on the relativistic nuclear energy density functional (RNEDF). For benchmark, we have performed the RNEDF calculations combined with the random-phase approximation (RPA). We evaluate the M1 excitation of $^{18}$O and $^{42}$Ca, whose sum-rule value (SRV) of the M1 transitions can be useful to test the computational implementation \cite{2019OP}. We also apply this RNEDF method to $^{208}$Pb, whose M1 property has been precisely measured \cite{1979Holt,1987Koehler,1988Laszewski,2016Birkhan}. Up to the level of the M1 sum rule, our result is in agreement with the experiments, except the discrepancy related with the quenching factors for $g$ coefficients.

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arXiv2019

Magnetic dipole excitation and its sum rule in nuclei with two valence nucleons

Background: Magnetic dipole (M1) excitation is the leading mode of nuclear excitation by the magnetic field, which couples unnatural-parity states. Since the M1 excitation occurs mainly for open-shell nuclei, the nuclear pairing effect is expected to play a role. As expected from the form of operator, this mode may provide the information on the spin-related properties, including the spin component of dineutron and diproton correlations. In general, the sum rule for M1 transition strength has not been derived yet. Purpose: To investigate the M1 excitation of the systems with two valence nucleons above the closed-shell core, with pairing correlation included, and to establish the M1 sum rule that could be used to validate theoretical and experimental approaches. Possibility to utilize the M1 excitation as a tool to investigate the pairing correlation in medium is also discussed. Method: Three-body model, which consists of a rigid spherical core and two valence nucleons, is employed. Interactions for its two-body subsystems are phenomenologically determined in order to reproduce the two-body and three-body energies. We also derive the M1 sum rule within this three-body picture. Conclusion: The introduced M1 sum rule can be utilized as a benchmark for model calculations of M1 transitions in the systems with two valence nucleons. The total sum of the M1 transition strength is related with the coupled spin of valence nucleons in the open shell, where the pairing correlation is unnegligible. The three-body-model calculations for 18 O, 18 Ne, and 42 Ca nuclei demonstrate a significant effect of the pairing correlations on the low-lying M1 transitions. Therefore, further experimental studies of M1 transitions in those systems are on demand, in order to validate proposed sum rule, provide a suitable probe for the nuclear pairing in medium, as well as to optimize the pairing models.

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arXiv2018

Supplemental note for "Two-fermion emission from spin-singlet and triplet resonances in one dimension"

Time-dependent calculation has been a suitable method to investigate the quantum dynamical processes. In Ref. [1] = [T. Oishi et al., J. of Phys. G 45, 105101 (2018)], we applied this method to the one-dimensional two-fermion tunneling in the nuclear-physics scale. Beside the specific results presented therein, some basic formalism and methods, which can be helpful for further discussions and developments to investigate time-dependent quantum systems, have been awaiting our description. This note is devoted to describe those supplemental contents. We do not limit the story to the nuclear physics, but keep it applicable to other scales and/or targets.

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arXiv2018

Time-dependent method for many-body problems and its application to nuclear resonant systems

The decay process of the schematic one-dimensional three-body system is considered. A time-dependent approach is used in combination with a one-dimensional three-body model, which is composed of a heavier core nucleus and two nucleons, with the aim of describing its evolution in two-nucleon emission. The process is calculated from the initial state, in which the three ingredient particles are confined. In this process, two different types of emission can be found: the earlier process includes the emission of spatially correlated two-nucleon pair, like a dinucleon, whereas, at a subsequent time, all the particles are separated from each other. The time-dependent method can be a suitable option to investigate the meta-stable and/or open-quantum systems, where the complicated many-body dynamics should necessarily be taken into account.

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