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Toshio Suzuki

Publications and source records attributed to Toshio Suzuki.

At least 19 recordsLinked to original sources
arXiv2025

Weak interaction rates of $sd$-shell Urca pairs in stellar environment using a shell-model approach

In this work, the weak interaction rates of $sd$-shell nuclei in the hot and dense stellar environment are calculated using the shell model. The {\it ab initio} effective interactions are employed for the calculation of Gamow-Teller strengths and weak rates in addition to the phenomenological interaction. The weak rates are evaluated in a fine grid of density and temperature. The electron capture and $β^-$-decay rates of Urca pairs of nuclei with $A = 23, 25, 29, 31$ and 33 are evaluated as a function of $\log_{10} ρY_e$ and the corresponding Urca density is obtained. The screening effects are also included for the evaluation of these stellar weak rates. In addition, the intrinsic cooling strength is evaluated for $A=29,31$ and 33 Urca pairs in neutron star crusts. The stellar weak rates, along with the neutrino energy emitted and the gamma heat production, are tabulated for $A = 29-39$ nuclei.

nucl-th↗
arXiv2025

Separation and Collapse of Equilibria Inequalities on AND-OR Trees without Shape Constraints

Herein, we investigate the zero-error randomized complexity, which is the least cost against the worst input, of AND-OR tree computation by imposing various restrictions on the algorithm to find the Boolean value of the root of that tree and no restrictions on the tree shape. When a tree satisfies a certain condition regarding its symmetry, directional algorithms proposed by Saks and Wigderson (1986), special randomized algorithms, are known to achieve the randomized complexity. Furthermore, there is a known example of a tree that is so unbalanced that no directional algorithm achieves the randomized complexity (Vereshchagin 1998). In this study, we aim to identify where deviations arise between the general randomized Boolean decision tree and its special case, directional algorithms. We show that for any AND-OR tree, randomized depth-first algorithms, which form a broader class compared with directional algorithms, have the same equilibrium as that of the directional algorithms. Thus, we get the collapse result on equilibria inequalities that holds for an arbitrary AND-OR tree. This implies that there exists a case where even depth-first algorithms cannot be the fastest, leading to the separation result on equilibria inequality. Additionally, a new algorithm is introduced as a key concept for proof of the separation result.

cs.AI↗
arXiv2025

Stellar $β^{-}$-decay rate of $^{63}$Ni and its impact on the ${s}$-process nucleosynthesis in massive stars

The $β^{-}$-decay rate of $^{63}$Ni, an important branching point, affects the subsequent nucleosynthesis in the weak component of the slow-neutron capture process (weak $s$-process). To evaluate the impact of the uncertainties of stellar lifetime of $^{63}$Ni on abundances, we calculate the contribution to $β^{-}$-decay rates from its excited states using the large-scale shell model with various interactions and also explore the atomic effects in the highly ionized plasma. In the core He burning stage and the shell C burning stage of massive stars, our new rates can be larger than those from Takahashi and Yokoi(1987) by up to a factor of 4 and 6, respectively. We evaluate the impact of the stellar decay rates of $^{63}$Ni on the nucleosynthesis of $A=60\sim90$ in a star with an initial mass of 25 $M_{\bigodot}$ and solar metalicity. We find that the new rates can lead to the abundance changes of $^{64}$Ni, $^{63}$Cu, $^{65}$Cu, $^{64}$Zn, $^{66}$Zn, $^{67}$Zn, and $^{68}$Zn by up to $18\%$, $14\%$, $7\%$, $98\%$, $16\%$, $15\%$, and $13\%$, respectively, after the shell C burning stage at the Lagrangian mass coordinate $M_{r}=2M_{\bigodot}$. The enhancement of the decay rate of $^{63}$Ni increases the weak $s$-process efficiency of nuclei after $^{65}$Cu.

astro-ph.HE↗
arXiv2025

Exploring the Neutrino Mass Hierarchy from Isotopic Ratios of Supernova Nucleosynthesis Products in Presolar Grains

We study the nucleosynthesis in a core-collapse supernova model including newly calculated neutrino-induced reaction rates with both collective and Mikheyev-Smirnov-Wolfenstein (MSW) neutrino-flavor oscillations considered. We show that the measurement of a pair of $^{11}$B/$^{10}$B and $^{138}$La/$^{139}$La or $^6$Li/$^7$Li and $^{138}$La/$^{139}$La in presolar grains that are inferred to have originated from core-collapse supernovae could constrain the neutrino mass hierarchy. The new shell-model and the model of quasi-particle random phase approximation in the estimate of three important neutrino-induced reactions, $ν+^{16}$O, $ν+^{20}$Ne, and $ν+^{138}$Ba are applied in our reaction network. The new rates decrease the calculated $^{7}$Li/$^{6}$Li ratio by a factor of five compared with the previous study. More interestingly, these new rates result in a clear separation of the isotopic ratio of $^{11}$B/$^{10}$B between normal and inverted mass hierarchies in the O/Ne, O/C, and C/He layers where $^{138}$La abundance depends strongly on the mass hierarchy. In these layers, the sensitivity of the calculated abundances of $^{10,11}$B and $^{6,7}$Li to the nuclear reaction uncertainties is also tiny. Therefore, we propose that the $^{11}$B/$^{10}$B vs. $^{138}$La/$^{139}$La and $^6$Li/$^7$Li vs. $^{138}$La/$^{139}$La in type X silicon carbide grains sampled material from C/He layer can be used as a new probe to constrain the neutrino mass hierarchy.

astro-ph.SR↗
arXiv2025

Mirror and triplet energy differences in $sd$-shell nuclei using microscopic interactions with isospin-symmetry breaking effects

In this study, we developed and tested two different isospin symmetry-breaking (ISB) versions of the microscopic DJ16A interaction. Starting with the isospin symmetric DJ16A interaction, we introduced two different Coulomb interactions- Coulomb-CD and Coulomb-w/SRC- along with phenomenological charge symmetry breaking (CSB) and charge independence breaking (CIB) effects. Then, we employed these interactions to calculate $b$- and $c$-parameters of the isobaric multiplet mass equation for $|T_z| = 1/2$ and $|T_z| = 1$ nuclei across the $sd$-shell. Our results indicate that the DJ16A$^\dagger$ interaction provides the most accurate $b$-parameter predictions between the two DJ16A-based interactions. Additionally, we explored mirror energy differences (MEDs) in low-energy spectra around $A = 20$ and demonstrated that large MEDs are primarily associated with high occupancies of the $1s_{1/2}$ orbital. Furthermore, $E2$ transition strengths were calculated using both DJ16A-based ISB interactions agreed with the experimental data, with minimal ISB effects observed on these transitions. Overall, the DJ16A$^\dagger$ interaction serves as a complementary set to the newly developed USD-family interactions, USDC, and USDCm and can be further tested for other mirror nuclei across the $sd$-shell to study nuclear structure properties and ISB effects in nuclear $β$-decay.

nucl-th↗
arXiv2024

The consistent analyses for determination of the point-nucleon distributions by electron and proton scatterings

Electron scattering cross section, as well as proton scattering cross section, observes the point-proton and the point-neutron distributions, but both cross sections are not able to determine them separately. If they are analyzed consistently with each other, there is a possibility to determine them with less ambiguity.The consistency can be examined through the moments of the charge distribution, which linearly depend on the moments of the point-proton and -neutron distributions.

nucl-th↗
arXiv2024

Shell-model study for allowed and forbidden $β^-$ decay properties in the mass region "south" of $^{208}$Pb

The large-scale shell-model calculations have been performed for the neutron-rich nuclei in the south region of $^{208}$Pb in the nuclear chart. The $β$-decay properties, such as the $\log ft$, average shape factor values, half-lives, and partial decay rates are calculated for these neutron-rich nuclei using recent effective interaction for the $^{208}$Pb region. These calculations have been performed without truncation in a particular model space for nuclei $N\leq 126$; additionally, particle-hole excitations are included in the case of core-breaking nuclei ($Z\leq 82, N>126$). An extensive comparison with the experimental data has been made, and spin parities of several states have been proposed.

nucl-th↗
arXiv2024

Study of the neutrino-oxygen cross sections of the charged-current reaction 16O($\barν_e,e^+$)16N(0 MeV,$2^-$) and the neutral-current reaction 16O($ν,ν$')16O(12.97/12.53 MeV,$2^-$), producing high-energy gamma rays

In the previous work, we discussed the cross section and the detection of 4.4-MeV $γ$ rays produced in the neutrino neutral-current (NC) reaction $^{16}$O($ν, ν^{\prime}$)$^{16}$O(12.97 MeV and 12.53 MeV, $2^-$) in a water Cherenkov detector at the low energy below 100 MeV. In this report, we further investigated both the charged-current (CC) reaction $^{16}$O($\barν_e, e^+$)$^{16}$N(0 MeV, $2^-$) and the NC reaction$^{16}$O($ν, ν^{\prime}$)$^{16}$O(12.97 MeV and 12.53 MeV, $2^-$), producing high-energy $γ$ rays, in which the more solid identification of the reactions can be applied via the coincidence method.

nucl-th↗
arXiv2023

Neutrino-induced reactions on 18O and implications of 18O mixture in water Cherenkov detectors on supernova neutrino events

Neutrino-nucleus reaction cross sections on 18O are evaluated by shell-model calculations and compared with those on 16O. Important contributions from Gamow-Teller transitions are noticed for 18O (ν_e, e^{-})18F in contrary to the case for 16O, where spin-dipole transitions are dominant contributions. Calculated cross sections for 18O(ν_e, e^{-})18F are shown to be larger than for 16O at low neutrino energies below 20 MeV in natural water with the 0.205% admixture of 18O due to the lower threshold energy (1.66 MeV) for 18O than that for 16O (15.42 MeV). The resulting electron spectra, that is, the cross sections as functions of emitted electron energy Te, are also shown to be quite different, reflecting the different threshold energies. The electron spectra from (ν_e, e^{-}) reactions on 18O and 16O in water Cherenkov detectors for supernova neutrino detection are investigated for both the cases with and without the neutrino oscillation and compared with those of the neutrino-electron scattering. It has been shown that the contribution from 18O (0.205% mixture) enhances the rates from 16O by 60% for the case without the oscillation and by 20-30% for the case with the oscillation below Te =20 MeV. For the case with the neutrino oscillation, the event rates for 18O and 16O become comparable to those of the neutrino-electron scattering. However, their rates at low energy (Te < 20 MeV) are much smaller than those of the neutrino-electron scattering, which is important for the pointing accuracy to the supernova direction.

nucl-th↗
arXiv2023

Label-free intratissue activity imaging of alveolar organoids with dynamic optical coherence tomography

An organoid is a three-dimensional (3D) in vitro cell culture emulating human organs. We applied 3D dynamic optical coherence tomography (DOCT) to visualize the intratissue and intracellular activities of human induced pluripotent stem cells (hiPSCs)-derived alveolar organoids in normal and fibrosis models. 3D DOCT data were acquired with an 840-nm spectral domain optical coherence tomography with axial and lateral resolutions of 3.8 μm (in tissue) and 4.9 μm, respectively. The DOCT images were obtained by the logarithmic-intensity-variance (LIV) algorithm, which is sensitive to the signal fluctuation magnitude. The LIV images revealed cystic structures surrounded by high-LIV borders and mesh-like structures with low LIV. The former may be alveoli with a highly dynamics epithelium, while the latter may be fibroblasts. The LIV images also demonstrated the abnormal repair of the alveolar epithelium.

physics.bio-ph↗
arXiv2023

Neutrino-induced neutral- and charged-current reactions on $^{40}$Ar

Neutrino-induced reactions on $^{40}$Ar are investigated by shell model for Gamow-Teller transitions and random-phase-approximation (RPA) for forbidden transitions. For the 1$^{+}$ multipole, an effective interaction in $sd$-$pf$ shell obtained by the extended Kuo-Krenciglowa (EKK) method from chiral interactions is used to study $B(GT)$, charged-current reaction $^{40}$Ar ($ν_e$, $e^{-}$) $^{40}$K, $B(M1)$ in $^{40}$Ar and neutral-current reaction $^{40}$Ar ($ν$, $ν$') $^{40}$Ar. A considerable quenching for spin modes is found in the analysis of $B(M1)$, and this quenching is taken into account for the evaluation of the cross sections of the neutral-current reaction. The sensitive dependence of the reaction cross sections on the quenching of the axial-vector coupling constant, $g_A$, is pointed out.

nucl-th↗
arXiv2023

Study of structure and radii for $^{20-31}$Na isotopes using microscopic interactions

In this work, Na isotopes with mass varying from $A=$ 20 to 31 have been studied using DJ16A, JISP16 and N3LO microscopic effective interactions in the $sd$-shell. These effective interactions are derived for $sd$-shell using no-core shell model wavefunctions and a unitary transformation method. We have also performed calculation with IMSRG effective interactions targeted for a particular nucleus. The studies include a detailed analysis of ground state binding energy, low-lying spectra, and electromagnetic properties such as reduced electric quadrupole transition strengths, quadrupole and magnetic dipole moments of the Na chain. The results obtained from these microscopic effective interactions were compared with the experimental data as well as with the results of phenomenological interaction USDB. The charge radii of Na isotopes are evaluated using shell model harmonic oscillator wave functions. In addition to charge radii, matter radii and neutron skin thickness in the Na chain are discussed with a focus on neutron-deficient Na isotopes.

nucl-th↗
arXiv2022

Detection of the 4.4-MeV gamma rays from $^{16}$O($ν, ν^{\prime}$)$^{16}$O(12.97 ${\rm MeV}, 2^-)$ with a water-Cherenkov detector in the supernova neutrino bursts

We first discuss and determine the isospin mixing of the two $2^-$ states (12.53 MeV and 12.97 MeV) of $^{16}$O nucleus using the inelastic electron scattering data. We then evaluate the cross section of 4.4-MeV $γ$ rays produced in the neutrino neutral-current (NC) reaction $^{16}$O($ν, ν^{\prime}$)$^{16}$O$(12.97 {\rm MeV}, 2^-$) in a water Cherenkov detector at the low energy below 100 MeV. The detection of $γ$ rays for $E_γ>5$ MeV from the NC reaction $^{16}$O($ν, ν^{\prime}$)$^{16}$O$(E_x>16\ {\rm MeV}, T=1$) with a water Cherenkov detector in the supernova neutrino bursts has been proposed and discussed by several authors previously. In this article, we discuss a new NC reaction channel from $^{16}$O(12.97 ${\rm MeV}, 2^-$) producing a 4.4-MeV $γ$ ray, the cross section of which is more robust and even larger at the low energy ($E_ν<25$ MeV) than the NC cross section from $^{16}$O$(E_x>16\ {\rm MeV}, T=1$). We also evaluate the number of such events induced by neutrinos from supernova explosion which can be observed by the Super-Kamiokande, a 32 kton water Cherenkov detector in the Earth.

astro-ph.HE↗
arXiv2022

Shell-model description for the properties of the forbidden $β^-$ decay in the region "north-east" of $^{208}$Pb

In the present work, we report a comprehensive shell-model study of the $\log ft$ values for the forbidden $β^-$ decay transitions in the north-east region of $^{208}$Pb. For this we have considered $^{210-215}$Pb $\rightarrow$ $^{210-215}$Bi and $^{210-215}$Bi $\rightarrow$ $^{210-215}$Po transitions. We have performed shell-model calculation using KHPE interaction in valence shell 82-126 for protons and 126-184 for neutrons without any truncation. We have also calculated half-lives and Q-values for the concerned nuclei. Recently several $\log ft$ values are observed corresponding to $β^-$ decay from (8$^-$) isomeric state of $^{214}$Bi$^m$ at CERN-ISOLDE facility [Phys. Rev. C {\bf 104}, 054301 (2021)], and for the first time we have reported shell-model results for these transitions.

nucl-th↗
arXiv2022

Systematic shell-model study on spectroscopic properties in the south region of $^{208}$Pb

We aim to study the properties of nuclei in the south region of $^{208}$Pb systematically, including the binding and excitation energies and electromagnetic properties, in order to predict unknown properties of these nuclei, such as isomerism, utilizing a theoretical model which describes the experimentally known properties precisely. We also address whether the $N=126$ shell closure is robust or not when the proton number decreases from $^{208}$Pb. We performed large-scale shell-model calculations with a new Hamiltonian suggested in the present work. The model space is taken as the five proton orbits within $50<Z\leqslant82$ and the thirteen neutron orbits within $82<N\leqslant184$. And one-particle one-hole excitation is allowed across the $N=126$ gap. The Hamiltonian is constructed by combining the existing Hamiltonians, KHHE (with adjustment of its proton-proton part) and KHPE, and the monopole based universal interaction. The shell-model results well reproduce the experimentally observed binding energies and spectroscopic properties, such as isomerism, core excitation, and electromagnetic properties. Some possible isomeric states in neutron-rich Pb, Tl, and Hg isotopes are predicted with transition energies and half-lives. We also examine the effective charges and the quenching of the $g$ factors suitable for this region by systematic comparisons between observed and calculated electromagnetic properties. A new Hamiltonian is constructed for nuclei in the south region of $^{208}$Pb, mainly including Pb, Tl, Hg, Au, Pt, Ir, Os, Re, and W isotopes around $N=126$, and provides them reasonable descriptions on nuclear properties including binding energies, excitation energies and electromagnetic properties through comprehensive and systematic studies.

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