Nucleosynthesis and Evolution of Neutron Stars

Jan 27, 2025, 1:00 PM → Jan 30, 2025, 4:30 PM Asia/Tokyo

Maskawa Hall (Kyoto University)

Akira Dohi (RIKEN), Eiji Kido (Institute for Cosmic Ray Research, University of Tokyo), Hidetoshi Yamaguchi (Center for Nuclear Study, the University of Tokyo), Masakiyo Kitazawa (YITP, Kyoto University), Nobuya Nishimura (The University of Tokyo), Tomoya Naito (RIKEN iTHEMS), Toru Tamagawa (RIKEN)

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[IMPORTANT NOTICE]

Please ignore any emails regarding the workshop from travel agencies or other companies that are not from the organizers or YITP, as we do not request accommodation support from any company (9 Oct. 2024).

You need a YITP Indico account to submit an abstract or register for participation. You can easily create one, but it takes several days for approval. See detail for this page (4 Nov. 2024).

Abstract submission deadline is extended by 10 Dec. 2024 (1 Dec. 2024).

The second circular is uploaded (16 Jan. 2025).

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[Scope of This Workshop]

The primary focus of this workshop is on the various “evolutions” of neutron stars, exploring the intersection of astrophysics theory and observation, as well as the connections to fundamental microphysics, including nuclear physics.

The specific themes of the workshop will include the long-term thermal evolution of neutron stars, their evolution in binary star systems (e.g., X-ray bursts, neutron star mergers), the evolution of matter in the universe (e.g., nucleosynthesis), and various other aspects of cosmic/galactic evolution. Additionally, we will explore future research possibilities in astronomy, nuclear physics, and fundamental physics through the lens of neutron star studies.

[Topics (Scientific Sessions)]

• Stellar evolution, supernovae, and formation of compact objects
• X-ray and other astronomical observation
• High-energy astrophysics and cosmic rays
• Hydrostatic and explosive nucleosynthesis
• Nuclear physics in neutron stars: Equation of states (EoS), fusion reactions, and radioactive decay
• Neutron stars and fundamental physics
• Other related topics in nuclear astrophysics

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[Invited Speakers]

• Aya Bamba (U. Tokyo, Japan): Supernovae, Compact objects, High-energy astronomy
• Toshihiro Fujii (Osaka Metropolitan U., Japan): High-energy cosmic rays
• Yuki Fujimoto (RIKEN, Japan): Neutron stars, QCD
• Tatsuya Furuno (Osaka U., Japan): Experimental nuclear physics related to astrophysics
• Duncan Galloway (Monash U., Australia): X-ray binaries
• Xu-Guang Huang (Fudan U., China/YITP, Kyoto U., Japan): QCD
• Oliver Just (GSI, Germany): Compact-object binaries, Nuclear EoS, Neutrino
• Koutarou Kyutoku (Chiba U., Japan): Compact-object binaries, Nuclear EoS, Gravitational waves
• Yi Hua Lam (IMP, CAS, China): X-ray bursts, Nuclear-structure calculation (shell model)
• Ang Li (Xiamen U., China): Nuclear-structure calculation (hyper nuclei), Neutron stars
• Lucy McNeill (RIKEN, Japan): Steller evolution, Supernovae
• Takayuki Miyagi (U. Tsukuba, Japan): Nuclear-structure calculation (ab initio)
• Nils Paar (U. Zagreb, Croatia): Nuclear-structure calculation (density functional theory)
• Hendrik Schatz (MSU, USA): Nuclear astrophysics experiments in FRIB
• Kimiko Sekiguchi (Science Tokyo, Japan): Nuclear-physics experiments (three-body interaction)
• Motoko Serino (Aoyama Gakuin U., Japan): X-ray bursts
• Daisuke Suzuki (U. Tokyo, Japan): Experimental nuclear physics in RIBF
• Yasutaka Taniguchi (Fukuyama U., Japan): Nuclear-theory calculation (cluster structure)

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[Venue]

Maskawa Hall (First floor of Maskawa Building for Education and Research), Kyoto University

京都大学 北部総合研究教育棟 1階 益川ホール

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[Fee (Tentative)]

• JPY 1,000 for coffee break etc. (for all the on-site participants)
• JPY 2,000 (students) or 4,000 (others) for banquet (for those who join)

Both fee should be paid by cash at the reception desk.

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[Important Dates]

[Related to Abstract Submission]

• Abstract submission deadline: 01 December 2024 10 December 2024 (Extended)
• Program announcement: January 2025

[Related to Registration]

• Registration deadline for in-person participation with the visa documents: 01 December 2024 10 December 2024 (Extended)
• Registration deadline for in-person participation: 08 January 2025
• Registration deadline for online participation: 25 January 2025

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[Announcement]

• First Circular (2024-10-04)

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[Organizers]

• Akira Dohi (CPR & iTHEMS, RIKEN)
• Eiji Kido (ICRR, U. Tokyo)
• Masakiyo Kitazawa (YITP, Kyoto U.)
• Tomoya Naito (iTHEMS, RIKEN/Dept. Phys., U. Tokyo; Co-Chair)
• Nobuya Nishimura (CNS, U. Tokyo/RIKEN/NAOJ; Co-Chair)
• Toru Tamagawa (CPR & Nishina Center, RIKEN)
• Hidetoshi Yamaguchi (CNS, U. Tokyo)

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This workshop is hosted by 

• Yukawa Institute for Theoretical Physics (YITP), Kyoto University

and sponsered by

• Center for Nuclear Study (CNS), The University of Tokyo
• Foundation for Promotion of Astronomy
• IReNA (International Research Network for Nuclear Astrophysics)
• UKAKUREN

 

Conference Photo

Circulars

• First Circular
• Program
• Second Circular

Monday, January 27

1:00 PM → 1:20 PM Registration

1:20 PM → 3:40 PM Oral Presentation: Session 1

Convener: Masakiyo Kitazawa (YITP, Kyoto University)

1:20 PM Opening

Speaker: Dr Nobuya Nishimura (The University of Tokyo)

27_01_Nishimura.pdf

1:30 PM Pre-supernova stellar structure and hydrodynamics leading to the formation of neutron star

It depends on the allocated time for the talk, but generally I plan to review recent developments in 3D neutrino / hydrodynamics simulations related to questions of minimum neutron star mass / fall back supernova / neutron star birth spin etc.

Speaker: Dr Lucy McNeill (RIKEN iTHEMS)

2:10 PM 3D simulations of supernovae: a systematic investigation of neutron star properties

Systematic studies of core-collapse supernovae (CCSNe) have been conducted based on hundreds of one-dimensional artificial models (O'Connor & Ott 2011,2013; Ugliano et al. 2013, Ertl et al. 2015) and two-dimensional self-consistent simulations (Nakamura et al. 2015;2019, Burrows & Vartanyan 2020). We have performed three-dimensional magnetohydrodynamic simulations for the core-collapse of 16 progenitor models covering ZAMS mass between 9 and 24 solar masses (Nakamura et al. 2024, MNRAS accepted, arXiv:2405.08367). Our CCSN models show a wide variety of shock evolution, explosion energy, as well as the properties of the central remnants including their mass and spin. We present the dependence of these explosion properties on the progenitor structure.

Speaker: Ko Nakamura (Fukuoka University)

27_03_Nakamura.pdf

2:35 PM Instabilities in chiral plasma

Chiral plasmas may exist in supernovae and neutron stars. We will discuss the unique instabilities inherent to chiral plasmas, with particular focus on a few newly found ones inclding the chiral magnetovortical instability, chiral Hall instability, and viscosity-induced instability. We will explore the potential implications of these instabilities in supernova and neutron star physics.

Speaker: Xu-Guang Huang (Fudan University)

27_04_Huang.pdf

3:15 PM Equation of state and neutrino emissivities with kaon condensates in hyperon-mixed matter

Various phases in dense matter, which may be realized in the inner core of neutron stars, have been investigated from viewpoints of nuclear and particle physics and astrophysics. In particular, strangeness degrees of freedom such as kaon condensates (KC) and hyperons (Y=$\Lambda$, $\Xi^-$, …) may appear in highly dense system. We have considered possible coexistence of KC and Y-mixed matter [(Y+K) phase] as multi-strangeness system and clarify equation of state (EOS) of highly dense hadronic matter with (Y+K) phase. We also discuss its relevance to extra neutrino emissivities in the presence of both KC and hyperons.
The interaction model for the description of the (Y+K) phase is based on chiral symmetry for kaon-baryon and kaon-kaon interactions, being combined with the relativistic mean-field theory for two-body baryon-baryon (B-B) interaction. In addition, universal three-baryon repulsive force (UTBR) and three-nucleon attractive force (TNA) are phenomenologically introduced, where unknown parameters are fixed to satisfy the saturation properties of symmetric nuclear matter.
It is shown that the EOS with the (Y+K) phase is stiff enough to be consistent with recent observations of massive neutron stars. We also discuss roles of main neutrino emissivities such as Kaon-induced Urca processes in the presence of nucleons and hyperons, on cooling of neutron stars, in particular, on extremely cold neutron stars recently observed.

Speaker: Takumi Muto (Chiba Institute of Technology)

27_05_Muto.pdf

3:40 PM → 4:10 PM Coffee Break

4:10 PM → 5:40 PM Oral Presentation: Session 2

Convener: Toru Tamagawa (RIKEN)

4:10 PM Recent progress on supernova remnants with XRISM X-ray satellite

Supernova remnants (SNRs) are one of the key tools for understanding the SN explosion mechanism and enrichment of the universe. We have launched the X-ray satellite XRISM, which enables us to carry out excellent spectroscopy for extended sources such as SNRs. In this talk, we will summarize the recent progress on SNRs with XRISM.

Speaker: Aya Bamba (U. Tokyo)

27_06_Bamba.pdf

4:50 PM Compact Star cooling with quark-hadron continuity

Neutron stars are high-density objects remained after a supernova explosion, in which the entire star is likened to a single atomic nucleus. Due to their high density exceeding the density of the nuclear density, it has been discussed that states and particles that do not appear in a normal nucleus can appear inside a neutron star. The realisation of superfluid states of neutrons and protons, and the appearance of quark matter and/or hyperons are considered to be possible. Such states have a significant impact on neutrino emission, the dominant cooling process in neutron stars, and appear in the thermal evolution of neutron stars. In particular, the superfluid state has a large effect on suppressing neutrino emission and has a significant impact on the thermal evolution of the neutron star. Comparison of temperature observations and cooling calculations of neutron stars allows us to constrain the internal state of the neutron star.
We have developed a model for the appearance of quark matter in a colour superconducting state in the core of a neutron star and performed cooling calculations. The colour superconducting state may have multiple pairings depending on the degree of freedom of the quark colour and flavour, we assume that the CFL(Colour-Flavour Locked) or 2SC (Two-Flavour Colour Superconducting) phases appear. We also introduced a quark-hadron continuity in which the ${}^3P_2$ superfluidity of neutrons in the hadronic phase on the low-density side is taken over by unpaired d-quarks in the 2SC phase on the high-density side, and we included that state (2SC+$

$ phase) in the cooling calculations.
We found that the cooling curves of neutron stars with the 2SC+$

$ phase pass through a higher temperature range than those with the 2SC phase, and are similar to the CFL phase. According to these results, we can conclude that the 2SC+$

$ phase can be realised in neutron stars having lower observed temperatures.

Speaker: Tsuneo Noda (Kurume Institute of Technology)

27_07_Noda.pdf

5:15 PM Exploring Physics Beyond the Standard Model via Temperature Observations of Neutron Stars

I will talk about how temperature observations of neutron stars provide a unique window to explore physics beyond the Standard Model of particle physics. The presence of hypothetical particles such as axions and dark matter, predicted by theories that extend the Standard Model, could alter the cooling behavior of the neutron stars. Axions, for example, increase cooling rates, while dark matter interactions could lead to additional heating. By comparing revised theoretical predictions with observed temperature evolution, we might explore signs of these elusive particles. The talk will be based on the following papers: arXiv:2309.02633, 2308.16066, 2204.02413, 2204.02238, 2008.03924, 1905.02991, 1904.04667, 1806.07151.

Speaker: Koichi Hamaguchi (University of Tokyo)

27_08_Hamaguchi.pdf

6:00 PM → 8:00 PM Banquet

Tuesday, January 28

9:30 AM → 10:50 AM Oral Presentation: Session 3

Convener: Dr Nobuya Nishimura (The University of Tokyo)

9:30 AM Impact of cluster resonances on low-energy nuclear fusion reactions

Theoretical evaluation of fusion reaction rates, critical in astrophysical phenomena, is essential because low-energy data, which are often difficult to measure directly, are required. This talk will discuss the effects of cluster resonances on 12C+12C and 12C+16O fusion reactions. Resonances drastically increase the cross section and thus can significantly impact the reaction rate. Theoretical evaluation of the properties of resonances, such as partial decay width, is also challenging because we must deal with the channel coupling of the entrance and exit channels. The general coupling potential is unknown, and we cannot treat it phenomenologically. In this talk, we treat various channel couplings employing a microscopic model to obtain resonance states and estimate their contribution to the fusion reaction.

Speaker: Yasutaka TANIGUCHI (Fukuyama University)

10:10 AM Nuclear reactions in accreting neutron stars at FRIB

Accreting neutron stars exhibit a broad range of nuclear reactions, from the rapid proton capture process in X-ray bursts at the surface to electron captures, neutron reactions, and fusion of neutron rich nuclei in the outer crust. These reactions give rise to a range of dynamic observables. At rare isotope beam facilities such as FRIB at MSU many of these reactions can now be studied. I will review the nuclear physics of accreting neutron stars, its link to observables, and results and prospects of experiments at FRIB to study these reactions.

Speaker: Hendrik Schatz (Michigan State University)

28_02_Schatz.pdf

28_02_Schatz.pptx

10:50 AM → 11:20 AM Coffee Break

11:20 AM → 12:25 PM Oral Presentation: Session 4

Convener: Dr Nobuya Nishimura (The University of Tokyo)

11:20 AM Multimessenger astronomy with compact binary mergers in light of O4

The LIGO-Virgo-KAGRA observation run 4 have found only a surprisingly small number of compact binary coalescences involving neutron stars. In this talk, I will discuss the current status and future prospects for multimessenger astronomy with neutron stars.

Speaker: Prof. Koutarou Kyutoku (Chiba University)

28_03_Kyutoku.pdf

12:00 PM Degeneracy corrections for stellar neutron capture rates and their implications for the R-process

Heavy element synthesis within stellar bodies typically manifests in explosive
environments such as neutron star mergers. These potential sites present high
enough neutron densities that facilitate neutron degeneracy. In this work, we
study the effect of neutron degeneracy on stellar capture rates for nuclei ranging
from stability to the neutron drip line. We investigate how degeneracy can alter
traditional reaction rates over a range of thermodynamic conditions that are
typical of the r - process. Our results show that degeneracy can change the
capture of neutrons by orders of magnitude compared to captures under strictly
explosive conditions. Furthermore, we demonstrate how thermally populated
targets can further enhance the capture of degenerate neutrons. Our corrections
to stellar neutron capture rates may lead to changes in the abundance evolution
of r-process elements.

Speaker: Bryn Knight (University of Guelph)

28_04_Knight.pdf

28_04_Knight.pptx

12:25 PM → 2:00 PM Lunch

2:00 PM → 4:10 PM Oral Presentation: Session 5

Convener: Tomoya Naito (RIKEN iTHEMS)

2:00 PM Hypernuclei Studies: A Key to Resolving the Hyperon Puzzle in Neutron Stars

TBA

Speaker: Prof. ANG LI (Xiamen University)

28_05_Li.pdf

2:40 PM Nuclear structure and dynamics at finite temperature in the relativistic nuclear energy density functional approach

Nuclear processes in stellar environments, such as those occurring in core-collapse supernovae and neutron star mergers, occur at extremely high temperatures, ranging from millions to billions of kelvin. These conditions differ markedly from the zero-temperature limit typically assumed in traditional nuclear studies. In a recent study, we presented the first comprehensive mapping of nuclear drip lines at finite temperatures, extending up to 23 billion kelvin, using the finite-temperature relativistic Hartree-Bogoliubov model combined with the particle continuum subtraction technique. Our results reveal a counterintuitive increase in the number of bound nuclei at elevated temperatures, attributed to the thermal quenching of shell effects, particularly for isotopes with closed neutron shells at N=82, N=126, and N=184. Additionally, we explored key nuclear properties such as neutron emission lifetimes, quadrupole deformations, neutron skin thickness, and pairing gaps as functions of temperature. While finite-temperature effects are modest up to approximately 1 MeV, they become more pronounced at higher temperatures, leading to reduced nuclear deformations and the weakening of shell closures. We also developed a novel theoretical framework for calculating gamma strength functions, nuclear beta decays, and electron capture at finite temperatures. These insights into the behavior of hot nuclei have important implications for understanding nuclear reactions in astrophysical environments, particularly in explosive stellar phenomena.

Speaker: Nils Paar (Faculty of Science University of Zagreb)

28_06_Paar.pdf

28_06_Paar.pptx

3:20 PM BARONET: A Lightweight Nuclear Network Geared Towards Coupling with Hydrodynamic Simulations

Accounting for out-of-NSE (nuclear statistical equilibrium) r-process nucleosynthesis is one of the most sought-after goals in the (numerical) modelling of binary neutron star (BNS) mergers. While post-processing analysis via full nuclear networks is a reliable technique, the computational and storage costs prevent such calculations to be directly coupled to hydrodynamic codes, thus neglecting the dynamical influence of the r-process heating. We present a novel framework, orthogonal to reduced networks, based on a careful selection and combination of the dominant degrees of freedom of nucleosynthesis and exploiting the "beta-flow" approximation, that drastically reduces the computational and storage requirements w.r.t. a full network while returning accurate predictions for both isotope abundances and heating rate. This technique features:
1) far less degrees of freedom than a full network (~300 vs. 8000);
2) explicit split between dominant/subdominant and fast/slow reactions;
3) ability to accurately track the time evolution of abundances and heating rate.
We summarize its base assumptions and derivation, practical implementation issues, and its application to parametrized BNS ejecta along with a detailed comparison w.r.t. to full networks such as SkyNet and WinNet. Finally, we show the first results of BNS merger simulations with inline nucleosynthesis performed with this model.

Speaker: Federico Maria Guercilena (Università di Trento)

28_07_Guercilena.pdf

3:45 PM Fermion Operator Expansion: Approach to Study Neutron Star Inner Crust

The pasta phases in the inner crust of neutron stars are crucial for understanding their behavior. However, simulating these phases using coordinate-space density functional theory is computationally expensive. In this contribution, we propose to perform such simulations effectively by the fermion operator expansion method. We apply this method to investigate the slab phases described by finite-temperature Hartree-Fock-Bogoliubov theory with band structure, and show that a concise identity exists between the generalized density matrix and the Fermi-Dirac distribution of the Hamiltonian (treated as a matrix function). We introduce an algorithm to compute the Fermi-Dirac distribution based on Chebyshev expansion. It yields results in good agreement with directly solving the equation of motion, but the time complexity is lower. Once nearsightedness is assumed, this method can further accelerate the computation. Therefore, the fermion operator expansion method is a powerful tool to study the nontrivial phases in neutron stars.

Speaker: Chengpeng Yu (University of Tsukuba)

28_08_Yu.pdf

4:10 PM → 4:40 PM Coffee Break

4:40 PM → 6:00 PM Poster Presentation: Poster

4:40 PM Application of the Accretion Torque Model to the X-ray Binary Pulsar A 0535+262

We studied how the neutron star's spin changes with the mass accretion rate in the X-ray binary pulsar A 0535+262. Using the long-term light curve obtained with the MAXI/GSC and the time variation of the pulse period from the Fermi/GBM, we found a clear anti-correlation between the bolometric luminosity and the period derivative. We applied the accretion torque model proposed by Ghosh and Lamb (1979) to the data. This model predicts the relation between the luminosity and the period derivative considering the physical parameters of the neutron star including the mass and radius, so the application of the model to the data enables us to estimate these parameters. We obtained a neutron star mass of 1.1-1.2 solar mass from the A 0535+262 data. In this presentation, we will present the details of the analysis and results and discuss possible uncertainties in the results produced by the model and the data.

Speaker: Toshihiro Takagi (Ehime University)

28_P_Takagi.pdf

4:40 PM Compact Objects in Modified Gravity

Compact objects are an interdisciplinary research subject in high-energy physics, and studying compact objects has become one of the significant concerns in modified gravity theory. Modifications of gravitational theory predict the modified TOV equation, and observations of compact objects allow us to test the theory in a strong and non-perturbative gravitational field. This talk will discuss the mass-radius relation of compact objects and the new physics predicted in F(R) gravity theory. We will also consider the importance of observables other than the mass-radius relation.

Speaker: Taishi Katsuragawa (Central China Normal University)

28_P_Katsuragawa.pdf

4:40 PM Complex-valued problem on FRG analysis of relativistic BEC

Although the relativistic Bose-Einstein condensates (BEC) of pion and kaon may emerge and impact the equation of state, the behavior of mesons in neutron stars is not well understood. The functional renormalization group (FRG) seems a promising tool to study the BEC formed through a second-order phase transition, where quantum fluctuations should be taken into account. Even in the local potential approximation, however, the flow equation becomes complex-valued, leading to complex thermodynamic quantities, while preceding works usually ignore their imaginary parts or keep the flow equation real-valued by restricting values of parameters.

We clarify the physics underlying in this complex-valued problem, and solve it by imposing a physically plausible condition for the effective potential and chemical potential. Applying the condition to the FRG of the complex scalar theory, we successfully extract the real-valued BEC from the complex flow equation and obtain phase diagrams on the temperature-chemical potential plane [1]. In order to observe the effect of quantum fluctuations, we also make a comparison with the phase diagrams in the mean-field approximation (MFA) [2]. The FRG phase transition line becomes closer to that of the MFA for weak interaction while it is more deviated for strong interaction. Our finding shows that quantum fluctuations become crucial for strong coupling, revealing the application range of the MFA. This work would lead to more accurate analyses of the pion-BEC in the core of neutron stars than the MFA and one-loop approaches [3].

[1] F. Terazaki, K. Mameda, and K. Suzuki, Relativistic BEC extracted from a complex FRG flow equation, (2024), arXiv:2409.04361 [hep-ph].
[2] J. I. Kapusta, Bose-Einstein Condensation, Spontaneous Symmetry Breaking, and Gauge Theories, Phys. Rev. D 24, 426 (1981).
[3] J. Bernstein and S. Dodelson, Relativistic Bose gas, Phys. Rev. Lett. 66, 683 (1991); K. M. Benson, J. Bernstein, and S. Dodelson, Phase structure and the effective potential at fixed charge, Phys. Rev. D 44, 2480 (1991).

Speaker: Fumio Terazaki (Tokyo University of Science)

28_P_Terazaki.pdf

4:40 PM Constraining of Nuclear Matter Equation of States with Rotating Neutron Stars

Since the advent of multi-messenger astronomy, nuclear physics constrains equation of state (EoS) for nuclear matter, particularly within neutron stars. Most studies attempting to impose such constraints have traditionally relied on spherical hydrostatic conditions described by the Tolman-Oppenheimer-Volkoff (TOV) equation. However, observational evidence shows that neutron stars are rotating, with some exhibiting very high angular velocities (milli-second pulsars). In 1989, Komatsu, Eriguchi, and Hachisu proposed a numerical method for modeling rapidly rotating general relativistic stars, now known as the KEH method, which initially used a polytropic EoS. In this research, we apply the KEH method using nuclear matter EoS derived from Skyrme and Gogny interactions. Additionally, through calculations of rotating neutron stars, we discuss implications to astrophysical constraints on these nuclear matter EoS in rapidly rotating neutron stars.

Speaker: Hyukjin KWON (Institute of Science Tokyo)

28_P_Kwon.pdf

4:40 PM Dineutron-dineutron correlation in 8He

There emerges strong spatial correlation in dilute neutron matters, which is called "dineutron", and its formation also occurs on the surface of nuclei. For example, 8He can be regarded as $\alpha+^2\mathrm{n}+^2\mathrm{n}$ 3-cluster system and recently, its enhancement was observed in $0_2^+$ state. In this talk, we focus on dineutron-dineutron correlation in $^8\mathrm{He}(0_2^+)$.
We will also focus on $^{12}\mathrm{C}(0_2^+)$ to discuss similarities and differences in terms of cluster correlation.

Speaker: Kosei Nakagawa (Kyoto University)

28_P_Nakagawa.pdf

4:40 PM Effect of Magnetic Field on Urca Processes in Neutron Star mergers

Isospin-equilibrating weak processes, called “Urca" processes, are of fundamental importance in astrophysical environments like (proto-)neutron stars, neutron star mergers, and supernovae. In these environments, matter can reach high temperatures of tens of MeVs and be subject to large magnetic fields. We thus investigate Urca rates at different temperatures and field strengths by performing the full temperature and magnetic-field dependent rate integrals for different equations of state. We find that the magnetic fields play an important role at temperatures of a few MeV, especially close to or below the direct Urca threshold, which is softened by the magnetic field. At higher temperatures, the effect of the magnetic fields can be overshadowed by the thermal effects. We observe that the magnetic field more strongly influences the neutron decay rates than the electron capture rates, leading to a shift in chemical equilibrium.

Speaker: Pranjal Tambe (Inter-University Centre for Astronomy and Astrophysics)

4:40 PM Impact of internal-conversion X-rays and nuclear isomers on X-ray and gamma ray emission from neutron-rich ejecta in a binary compact-star merger

In the gravitational wave event GW170817, observed in 2017, electromagnetic counterparts were identified in a wide range of wavelengths from radio to gamma rays for the first time. A kilonova (AT2017gfo) was detected in visible and infrared bands and powered by the radioactive-decay heat of neutron-rich nuclei synthesized via the rapid neutron-capture process (r-process). Furthermore, heavy elements such as Sr and Te, whose production is theoretically expected via the r-process during a binary neutron star merger, were observationally confirmed by identifying infrared spectral lines. The optical and infrared light curves and spectral evolution strongly suggest the synthesis of lanthanides ($Z = 57–71$). However, the observational confirmation of third-peak nuclei ($Z \sim 80$), which are also theoretically expected to form, remains elusive. In this study, we calculate the time evolution of nuclear gamma-ray and internal-conversion X-ray fluxes originating from the decay of neutron-rich nuclei synthesized via the r-process in gas ejected during compact star mergers.

Employed with the same spherical symmetric, constant-velocity expansion model for the ejecta from a binary compact-star merger and nuclear reaction network as our previous work (Terada et al. 2022), we estimate the time evolution of temperature, density, and chemical composition in the ejecta, with the electron fraction ($Y_e$) as a parameter. We focus on internal-conversion X-rays and nuclear gamma rays, comprehensively considering the effects of nuclear isomers and internal-conversion X-rays, which have been understudied or unexamined in the past. We focus on the epoch within approximately one month after the merger. Our findings are as follows:
(1) We identify the flux enhancement below approximately 100 keV due to internal-conversion X-rays, particularly over one-order-of-magnitudes increase below the 60–70 keV range;
(2) Plenty of internal-conversion X-ray lines are emitted with high fluxes from the ejecta with high neutron excess $Y_e \le 0.20$;

Speaker: Dr Shin-ichiro Fujimoto (Kumamoto Kosen)

28_P_Fujimoto.pdf

4:40 PM Impacts of multineutrons on nuclear compositions and neutrino reaction rates in core-collapse supernova

The neutrino reactions play a pivotal role in determining the dynamics of core-collapse supernovae such as the contraction of the proto-neutron star and the shock wave revival. However, most simulations have not considered the detailed neutrino reactions with light elements, which are found to be abundant in supernovae at subsaturation density [1]. Previous studies have shown the weak interactions may affect the shock wave revival [2, 3, 4]. Meanwhile, some experiments and theoretical calculations suggest the quasibound systems consisting of only multiple neutrons, or multineutrons [5]. They might appear in the central region, since the matter is neutron-rich and at high-temperature [6].
To investigate their impacts, we calculated the nuclear compositions and charge-current neutrino reaction rates in the central region of the core-collapse supernova, assuming the existence of the dineutron and tetraneutron. Our results show that their presence suppresses the neutrino reactions that convert neutrons into protons, while enhancing reactions that convert protons into neutrons. The fast neutronization and contraction of the proto-neutron star may occur, leading to increased neutrino emissions and contributing to the supernova explosion or the early birth of neutron stars.

[1] Shun Furusawa and Hiroki Nagakura. Nuclei in core-collapse supernovae engine. Prog. Part. Nucl. Phys., 129:104018, 2023.
[2] Tobias Fischer, Stefan Typel, Gerd R¨opke, Niels-Uwe F. Bastian, and Gabriel Mart´ınez-Pinedo. Medium modifications for light and heavy nuclear clusters in simulations of core collapse supernovae – Impact on equation of state and weak interactions. Phys. Rev. C, 102(5):055807, 2020.
[3] Shun Furusawa, Hiroki Nagakura, Kohsuke Sumiyoshi, and Shoichi Yamada. The influence of inelastic neutrino reactions with light nuclei on the standing accretion shock instability in core-collapse supernovae. Astrophys. J., 774:78, 2013.
[4] Naofumi Ohnishi, Kei Kotake, and Shoichi Yamada. Inelastic Neutrino-Helium Scatterings and Standing Accretion Shock Instability in Core-Collapse Supernovae. Astrophys. J., 667:375–381, 2007.
[5] F. Miguel Marqu´es and Jaume Carbonell. The quest for light multineutron systems. Eur. Phys. J. A, 57(3):105, 2021.
[6] I. V. Panov and A. V. Yudin. Light Neutral Clusters in Supernova Matter. Phys. Atom. Nucl., 82(5):483–490, 2019.

Speaker: Tatsuya Matsuki (Tokyo University of Science)

28_P_Matsuki.pdf

4:40 PM Long-term supernova simulation with axion-like particles

Supernovae emit their energy mostly as neutrinos. If a galactic supernova occurs, some of thousands of neutrinos are likely to be detected in Super-Kamiokande (SK) for more than a minute. Supernovae have high temperature environments so that beyond standard model particles such as axions are likely to be produced. In this study, we implemented a supernova simulator with the effects of axion-like particles to calculate changes of neutrino emissions. Finally, I will discuss observation of neutrinos from such supernovae in SK.

Speaker: Masamitsu Mori (National Astronomical Observatory of Japan)

28_P_Mori.pdf

4:40 PM Mechanisms in production of evaporation residue for multinucleon transfer reactions with heavy nuclei

There is a limit to the production of neutron-rich nuclei by traditional fusion reactions. Therefore, in recent years, multi-nucleon transfer (MNT) reactions have attracted attention as a method of producing neutron-rich nuclei [1]. However, the reaction mechanism is not yet well understood due to its novelty and complexity. In the future, it will be necessary to estimate the physical quantity of evaporation residue (ER) in the production of neutron-rich isotopes in heavy and superheavy elements. In this study, we construct a dynamical model that describes the dynamics of the MNT reaction and verify the model by comparing it with experimental data to clarify the reaction mechanism.

This study aims to deal with the production of neutron-rich nuclei in heavy and superheavy elemental regions. As a first step, to clarify the reaction mechanism, we studied the angular momentum of the ER produced by MNT reaction and the emission angle of projectile-like nuclei. In the region of heavy and superheavy nuclei, it is known that the fission process of ERs depends on their angular momentum, and information about angular momentum is important to know the survival probability of the ER [2]. The emission angles of projectile-like nuclei are also experimentally observable data, which are necessary for angular momentum prediction. There is a correlation between angular momentum and the emission angle of projectile-like nuclei.

Our theoretical model is based on the two-center shell model to describe the configuration of nuclei [3]. The time evolution of the configuration is described by the multidimensional Langevin equation [4]. In this presentation, we show the dynamics of the MNT reaction using parameters fitted with preliminary experimental data. We will discuss the factors we need to know about in future reactions between heavy nuclei. The effect of the angular momentum of ERs on the following fission process is also discussed.

References
[1] V. Zagrebaev, et al., Phys Rev C 73, (2006) 031602.
[2] S. Tanaka, et al., Phys. Rev. C 105, (2022) L021602.
[3] J. Maruhn and W. Greiner, Z. Phys 251, (1972) 431.
[4] V. Zagrebaev and W. Greiner, J. Phys. G 34, (2007) 2265-2277.

Speaker: Kohta Nakajima (Kindai Univ.)

4:40 PM Modeling a new "Clocked" X-ray Burster SRGA J144459.2--604207

Type-I X-ray bursts, which are nuclear-burning aided brightening phenomena on the surface of accreting neutron stars, have often been observed, and most of them show irregular behavior of light curves. However, some X-ray bursters show very regular behavior, often called "Clocked" bursters, which enable us to probe the properties of accreting neutron stars and the accreted matter by comparing theoretical models with observed light curves. In this talk, we present our X-ray burst models for the newly observed Clocked burster, SRGA J144459.2-604207. We discuss the compositions of accreted matter in SRGA J1444. While all previous Clocked bursters are likely to have solar-like compositions of accreted matter, SRGA J1444 is shown to be the first Clocked burster with non-solar elemental compositions.

Speaker: Akira Dohi (RIKEN)

4:40 PM Nuclear properties at neutron-rich region

Nucleosynthesis heavier than iron is critically driven by the rapid neutron capture process (r-process), where atomic nuclei capture neutrons faster than they undergo beta decay. The r-process requires a neutron-rich environment and involves the formation of neutron-rich nuclei. This study investigates the physical properties of neutron-rich nuclei, focusing on octupole deformation and the neutron drip line.

In this work, we employed Skyrme-type density functional theory and have performed systematic calculations using the HFBTHO code (the Skyrme-Hartree–Fock–Bogolyubov solver using the harmonic oscillator basis), that is able to describe axially symmetric deformations without reflection symmetry. This presentation will focus on nuclei in the actinide region, which are known to exhibit octupole deformation. We will report the changes of canonical single-particle neutron energies as a function of octupole deformation.

Additionally, we explored the connection between the limits of nuclear existence in neutron-rich regions and the influence of electromagnetic interaction. Our findings demonstrate that electromagnetic force can expand the neutron drip line in multiple nuclei. The mechanisms of this phenomenon will be reported from a quantum mechanical perspective.

Speaker: Kenta Hagihara (University of Tsukuba)

XRB2025.pdf

4:40 PM Production probability of new superheavy element using dynamical model

In recent years, the synthesis of new superheavy element (SHE) has been paid attention around the world. When synthesizing SHEs, hot fusion using 48Ca as projectile and actinides as targets is successful for many SHEs up to Og (Z=118) [1,2]. In synthesizing SHEs after Z=119 by hot fusion, if 48Ca is used as projectile, it is necessary to use nuclides after Es (Z=99) as targets. However, nuclides after Es (Z=99) have so short half-lives, it is not practical to use them as targets. Therefore, to synthesize SHEs after Z=119, it is necessary to use projectile with a higher number of protons than 48Ca. This allows the target to be determined relatively stable nuclide in actinides.

The synthesizing of SHEs includes touching process, formation process, and decay process. We calculate evaporation residue cross section by combining three probabilities of these processes. The touching probability is calculated by coupled-channel method [3,4]. The formation probability of compound nucleus is calculated by dynamical model with Langevin equation [3]. And the survival probability of excited compound nucleus is calculated by statistical model [5]. In this study, we calculated the evaporation residue cross sections using 48Ca and 50Ti, 51V, 54Cr, which have more protons than 48Ca, as projectiles and actinides as targets. And we analyzed the effect of difference in combination of projectiles and targets on cross sections.

We mainly discuss the effects of reaction Q-value and Coulomb barrier height in the evaporation residue cross sections. We use Q-value that depends on the mass tables. And we use Bass model to estimate the Coulomb barrier height. The values of these parameters differ depending on the combinations of nuclei, and these parameters play very important roles in the estimation of the excitation functions of cross sections. In this presentation, better combinations of projectiles and targets in the synthesis of new superheavy elements will be discussed.

References
[1] Yu. Ts. Oganessian, et al., Phys. Rev. C 70, 064609 (2004).
[2] Yu. Ts. Oganessian, et al., Phys. Rev. C 74, 044602 (2006).
[3] Y. Aritomo, et al., Phys. Rev. C 85, 044614 (2012).
[4] K. Hagino, et al., Computer Physics Communications 123 (1999) 143-152.
[5] Y. Aritomo, et al., Phys. Rev. C 59, 769, February 1999.

Speaker: Kosuke Kawai (Kindai University)

4:40 PM Prompt follow-up observation of the X-ray transient MAXI J1752−457 with the CubeSat X-ray observatory NinjaSat

Prompt follow-up observation of the X-ray transient MAXI J1752−457 with the CubeSat X-ray observatory NinjaSat.

Speaker: Amira Aoyama (Tokyo University of Science)

28_P_Aoyama.pdf

4:40 PM Sensitivity Study of Type-I X-ray Burst To Nuclear Reaction Rates

Neutron stars in low-mass X-ray binaries, accreting hydrogen- or helium-rich material from a companion star, frequently exhibit thermonuclear runaways on their surfaces known as Type-I X- ray bursts (XRBs). These bursts are powered by nuclear processes, such as the triple-α process, the αp process, and rapid proton capture process, which play a critical role in model-observation comparisons. In this study, we investigate the impact of nuclear reaction uncertainties on XRBs using the ONEZONE model (Cyburt et al., 2016), considering different accreted compositions and accretion rates for the binary systems that are within the range of observed burst sources. The study is carried out in two stages. First, we determine the burst ignition conditions by simulating the settling of the accreted material with a full reaction network and a semi-analytical model. Second, we perform a sensitivity analysis by varying proton- and alpha-induced reaction rates in JINA REACLIBV2.2 within their estimated uncertainties. We explore the influence of these reactions on the XRBs light curve and the neutron star crust composition. The findings highlight key nuclear reactions that significantly affect XRB observables and the final abundances produced, offering guidance for future experimental efforts to improve our understanding of the uncertainties in the reaction rates involved in XRBs.
This work was supported by U.S. DOE grant DE-SC0022538 and by NSF grant PHY-1430152 (JINA Center for the Evolution of the Elements).

Speaker: Irin Sultana (Central Michigan University)

28_P_Sultana.pdf

4:40 PM The impacts of nuclear reaction uncertainties on explosive nucleosynthesis of core-collapse supernovae

Massive stars ($> 10 M_\odot$) undergo core-collapse supernova explosions at the end of their evolution. These explosions release elements ranging from helium to the iron peak, which are (produced during the stellar evolution) to iron peak elements (synthesized in explosive nucleosynthesis near the supernova core region). Although the explosion mechanism of core-collapse supernovae is not fully understood, 1D spherically symmetric explosion models have been constructed that relatively well reproduce the observed elemental abundances. Such models are ideal to systematically study the impact of nuclear reaction rates on the nucleosynthesis. Some of the nuclear reactions in explosive nucleosynthesis, certain nuclear reactions can be accessed through accelerator experiments, offering the potential to investigate undetermined reaction rates that are important in astrophysics. We have developed a nucleosynthesis code with Monte-Carlo framework that accounts for the uncertainties in nuclear reaction rates and applied it to processes beyond iron. Given its general applicability, our framework is naturally suited for studying explosive nucleosynthesis in supernovae. In this study, we investigate 1D explosion models using the "PUSH" method, which simulates explosions by mimicking the enhanced neutrino heating observed in multi-dimensional simulations. We focus on nucleosynthesis in progenitors with solar and sub-solar metallicity and metal-poor representatives of masses around $M_{\rm ZAMS} = 16 M_\odot$. Detailed post-process nucleosynthesis calculations with Monte Carlo analysis is employed to comprehensively explore the effects of uncertainties in relevant reaction rates. Additionally, we identify "key reaction rates" for explosive nucleosynthesis based on statistical analysis of our Monte Carlo nucleosynthesis calculations.

Speaker: Dr Nobuya Nishimura (The University of Tokyo)

28_P_Nishimura.pdf

4:40 PM The triple-alpha reaction at low temperatures by an exact three-body model

The triple-alpha reaction plays a significant role in nucleosynthesis heavier than 12C and concomitant stellar evolution [1]. The reaction rates of this reaction at the helium-burning temperatures, T_9 > 0.1, are dominated by the sequential process via two narrow resonances: alpha+alpha -> 8Be(0+_1: g.s.), 8Be+alpha -> 12C(0+_2: E=0.379 MeV) [2,3], and they have been understood relatively well through the studies of the Hoyle state. T_9 is temperature in unit of 10^9 K; E is the center-of-mass energy to the 3 alpha threshold in 12C. In contrast, the direct triple-alpha process from ternary continuum states, alpha+alpha+alpha -> 12C, for T_9 < 0.1 still seems to remain in an open question. The direct process corresponds to the non-resonant component in [4], and it is thought to be important in the astrophysical sites of novae, X-ray bursts, and Type-Ia SNe, leading to the nucleosynthesis of the hot CNO cycle and rp-process [5].

In NACRE [2], 8Be is assumed to be bound as a particle, and the reaction rates have been estimated by an improved model based on the pioneering works of [4]. To determine the rates more dynamically, the methods with hyper-spherical coordinates are used in [6-9], and the Coulomb modified Faddeev method is adopted in [10]. Whereas 8Be continuum states are treated adiabatically in [8-10], the direct process is calculated non-adiabatically in [6,7].

In this presentation, I discuss the direct triple-alpha process by using a non-adiabatic Faddeev hyper-spherical harmonics and R-matrix (HHR$^\ast$) expansion method [6]. I illustrate that the calculated photo-disintegration cross sections of 12C(2+_1(E=-2.835 MeV) -> 0+) of HHR$^\ast$ are much smaller than those of the recent adiabatic models [9,10] for 0.15 < E < 0.35 MeV. The resultant rates have the strong temperature dependence at T_9 = 0.1, as well as NACRE, and their numerical values are expressed in a simple analytic form. From the comparison between the calculations, I find that the current standard rates [2,3] can be reduced by about 10^-4 at T_9 ~ 0.05, because of the accurate description of 8Be break-up. As an example of new rates, I also examine the ignition critical density [4] of helium burning in accreting white dwarfs. The present model with [11] leads to the ignition density of about (3 x 10^8) g cm^-3 at T_9= 0.01, which seems to be consistent with [4]. Due to the reduction of the rate at T_9= 0.05, the derived ignition density appears to be insensitive to the temperatures in 0.01 < T_9 < 0.05.

[1] F. Hoyle, ApJ Suppl. Ser. 1, 121 (1954); E.E. Salpeter, ApJ 115, 326 (1952).
[2] C. Angulo, M. Arnould, M. Rayet, et al., Nucl. Phys. A 656, 3 (1999).
[3] G.R. Caughlan, W.A. Fowler, At. Data Nucl. Data Tables 40, 283 (1988).
[4] K. Nomoto, F.-K. Thielemann, S. Miyaji, Astron. Astrophys. 149, 239 (1985); K. Langanke, M. Wiescher, F.-K. Thielemann, Z. Phys. A 324, 147 (1986).
[5] R.K. Wallace, S.E. Woosley, T. Weaver, ApJ 258, 696 (1982); R.K. Wallace, S.E. Woosley, ApJ Suppl. 45, 389 (1981).
[6] M. Katsuma, arXiv:2411.03600; arXiv:2302.03844; Communications in Physics vol.32 no.4S 585 (2022).
[7] N.B. Nguyen, F.M. Nunes, I.J. Thompson, PRC 87, 054615 (2013); N.B. Nguyen, F.M. Nunes, I.J. Thompson, E.F. Brown, PRL 109, 141101 (2012).
[8] D.V. Fedorov, A.S. Jensen, PLB 389, 631 (1996).
[9] H. Suno, Y. Suzuki, P. Descouvemont, PRC 94, 054607 (2016).
[10] S. Ishikawa, PRC 87, 055804 (2013); ibid. 90, 061604 (2014).
[11] E.E. Salpeter, H.M. Van Horn, ApJ 155 (1969) 183; N. Itoh et al., ApJ 234, 1079 (1979).

Speaker: Masahiko Katsuma (Osaka City University & Universite Libre de Bruxelles)

28_P_Katsuma.pdf

4:40 PM Ultra high energy cosmic rays in large-scale astrophysical structures: neutron production and implications for cosmic ray confinement and escape

Cosmic rays are often modeled as charged particles. This allows their non-ballistic propagation in magnetized structures to be captured. In certain situations, a neutral cosmic ray component can arise. For example, cosmic ray neutrons are produced in considerable numbers through hadronic pp and p-gamma interactions. At ultrahigh energies, the decay timescales of these neutrons is dilated, allowing them to traverse distances on the scale of galactic and cosmological structures. Unlike charged cosmic rays, neutrons are not deflected by magnetic fields. They propagate ballistically at the speed of light in straight lines. The presence of a neutral baryonic cosmic ray component formed in galaxies, clusters and cosmological filaments can facilitate the escape and leakage of cosmic rays from magnetic structures that would otherwise confine them. We show that, by allowing confinement breaking, the formation of cosmic-ray neutrons by high-energy hadronic interactions in large scale astrophysical structures can modify the exchange of ultra high-energy particles across magnetic interfaces between galaxies, clusters, cosmological filaments and voids.

Speaker: Ellis Owen (RIKEN)

28_P_Owen.pdf

4:40 PM Urca Pair $^{63}$Fe-$^{63}$Mn and its Impact on the Thermal Evolution of Neutron Star Crust

The Urca cooling strength of $^{63}$Fe-$^{63}$Mn exhibits a large range of variation due to the the uncertainty in the spin-parity of ground state of $^{63}$Fe, which is approaching the Island of Inversion at $N=40$, characterized by large nuclear deformation. To investigate the cooling effect on the thermal evolution of neutron star crust, we preformed simulations by using models for computing neutron star structure and evolution. Cooling strength obtained from various experiments on the $\beta ^{-}$ decay of $^{63}$Mn are included in this work. When adopting data recommended by NNDC, the cooling strength of $^{63}$Fe-$^{63}$Mn pair could have significant impact on the crust thermal evolution of neutron star including the crust cooling in quiescent phase and on the superburst ignition. More precise measurements of the $\beta^{-}$ decay of $^{63}$Mn are needed to better understand the Urca cooling effect of the $^{63}$Mn-$^{63}$Fe pair, as well as other potential Urca pairs in the neutron-rich region.

Speaker: Hao Huang (Institute of Modren Physics, Chinese Academy of Science)

28_P_Huang.pdf

Wednesday, January 29

9:30 AM → 10:50 AM Oral Presentation: Session 6

Convener: Nils Paar (Faculty of Science University of Zagreb)

9:30 AM New Perspectives on Dense QCD Matter

I will present new perspectives on the properties of matter at high baryon density and low temperatures with the application to the description of neutron stars in mind. In particular, I will discuss the role of QCD in constraining the equation of state and the possible duality in dense matter, known as Quarkyonic duality.

Speaker: Yuki Fujimoto (University of California, Berkeley / RIKEN)

29_01_Fujimoto.pdf

10:10 AM Equation-of-state constraints from helium in kilonovae

Neutron-star mergers are excellent laboratories for stuying the properties of high-density matter. I will report our recent study modeling the imprint of helium absorption features in kilonova spectra, which revealed that the kilonova accompanying GW170817 likely did not harbor significant amounts of helium. I will discuss the implications of this finding for the lifetime of the neutron-star remnant and for the equation-of-state related properties of cold neutron stars.

Speaker: Oliver Just (GSI Darmstadt)

29_02_Just.pdf

10:50 AM → 11:20 AM Coffee Break

11:20 AM → 12:25 PM Oral Presentation: Session 7

Convener: Nils Paar (Faculty of Science University of Zagreb)

11:20 AM Recent progress of nuclear astrophysics at RI Beam Factory

Speaker: Daisuke Suzuki (RIKEN Nishina Center)

12:00 PM $\beta$-decay half-life as an indicator of shape-phase transition in neutron-rich Zr isotopes

$\beta$-decay half-life is sensitive to the shell structure near the Fermi levels. Nuclear deformation thus impacts the $\beta$-decay properties.
A first-order shape-phase transition in neutron-rich Zr isotopes is predicted by some models. We investigate the $\beta$-decay half-lives of neutron-rich nuclei around $^{110}$Zr, where the shape-phase transition is predicted to occur, to see if the $\beta$-decay half-life can be an indicator of the shape changes.
To do that, the proton-neutron quasiparticle random-phase approximation (RPA) is adopted to calculate the Gamow-Teller transitions. In addition, we apply the quasiparticle phonon-vibrational coupling (PVC) to consider the phonon couplings. Then, we found that the spherical and oblate configurations give similar half-lives but shorter ones than the prolate configuration at the RPA level. The PVC effect further reduces the half-lives in general, but the effect is smaller for the deformed configuration than that for the spherical one. As a result, it makes the shape change from the oblate configuration to the spherical configuration visible. Therefore, a sudden shortening of $\beta$-decay half-lives is always found at the nuclear shape changes.

Reference:
K. Yoshida, Y. Niu, and F. Minato, Phys. Rev. C 108 (2023), 034305.

Speaker: Kenichi Yoshida (RCNP, the University of Osaka)

29_04_Yoshida.pdf

12:25 PM → 2:00 PM Lunch

2:00 PM → 3:20 PM Oral Presentation: Session 8

Convener: Hidetoshi Yamaguchi (Center for Nuclear Study, the University of Tokyo)

2:00 PM Nuclear ab initio calculation for astrophysics

The range of applicability of nuclear ab initio calculations is expanding. Owing to developments in, for example, chiral effective field theory and renormalization group techniques, we are now able to obtain results that maintain a connection to the underlying theory of the strong interaction, quantum chromodynamics. By introducing a new storage scheme for the three-body matrix elements, we can now compute properties of heavy-mass nuclei, enabling the investigation of experimentally challenging quantities. In this presentation, I will introduce our current activities relevant to astrophysics, based on the valence-space in-medium similarity renormalization group approach, a powerful many-body method. These activities include calculations of mass and beta-decay half-lives in neutron-rich nuclei.

Speaker: Takayuki Miyagi (University of Tsukuba)

2:40 PM Experimental approach to three-nucleon forces – recent topics -

Understanding the strong nuclear force is fundamental to understanding the formation of matter in the Universe. Since Yukawa’s meson theory, the nuclear force has been formulated in terms of two-nucleon interactions. Three-nucleon forces (3NFs), which appear when more than two nucleons interact, have been revealed in the last two decades. The establishment of high-precision two-nucleon potentials and the achievements of the ab-initio calculations with these forces suggest the necessity of 3NFs in describing various nuclear phenomena, including the equation of the state of nuclear matter.

Few nucleon systems offer opportunities to investigate three-nucleon forces by directly comparing rigorous numerical calculations with high-precision experimental data. To explore the 3NFs, experimental programs using the polarized beam and polarized target systems are in progress at RIKEN and RCNP in Japan. I will review the three-nucleon force study from an experimental point of view and discuss the impact of these forces in nuclear physics and related fields.

Speaker: Kimiko Sekiguchi (Institute of Science Tokyo)

29_06_Sekiguchi.pdf

3:20 PM → 3:50 PM Coffee Break

3:50 PM → 5:05 PM Oral Presentation: Session 9

Convener: Hidetoshi Yamaguchi (Center for Nuclear Study, the University of Tokyo)

3:50 PM Production of heaviest nuclei in compact binary mergers

Since the discovery of the kilonova associated with GW170817, neutron star mergers have been regarded as astrophysical sites of the r-process nuclei. However, it remains a mystery how the robustness of the r-process patterns (or universality) in metal-poor stars can be explained. The mechanism that leads to high Th/Eu ratios (actinide boost) has not been well understood, either. In this talk, we discuss the r-process in the ejecta from the mergers of binary neutron stars or a neutron star and a black hole with the aim of solving these problems (universality and actinide boost). The nucleosynthesis is based on the long-term, GRMHD, neutrino-transport simulations of binary mergers, which self-consistently follow the evolution of both dynamical and post-merger phases.

Speaker: Shinya Wanajo (Tohoku University)

29_07_Wanajo.pdf

4:15 PM Discovering the most important temperatures of helium burning reactions in pair-instability supernova nucleosynthesis

Pair-instability supernovae (PISNe) are the final fates of massive stars with an initial mass ranging from 140-260 $M_{\odot}$. Due to the efficient $^{56}\mathrm{Ni}$ nucleosynthesis, PISNe can be very luminous phenomena. According to some previous works, not only the PISN progenitor evolution but also the PISN nucleosynthesis is affected from $^{12}{\rm C}(\alpha,\gamma)^{16}{\rm O}\,$ reaction rate strongly. However, these works are based on the reaction rate tables changed high or low in all temperature despite the strong dependence of nuclear reactions on temperature. In this work, we considered the most important temperatures of helium burning reactions for $^{56}\mathrm{Ni}$ nucleosynthesis in PISN using Monte Carlo methods, specifically, we simulated the stellar evolution with randomized helium burning reaction rates,and we obtained the strong correlated temperature for these reactions. In this presentation, we will report the details of the results.

Speaker: Hiroki Kawashimo (The University of Tokyo, Komaba)

29_08_Kawashimo.pdf

4:40 PM GPE Calculations for Superfluid Neutron Quantum Vortices and Superconducting Proton Fluxtubes in Neutron Stars

Neutron stars exhibit sudden changes of its rotational velocity, known as "pulsar glitches". It has been believed that glitches are mainly caused by superfluid neutron vortices in the inner crust of neutron stars. However, importance of contributions of the outer core has been recently discussed, and further microscopic investigations of quantum vortices and flux-tubes in the outer core of neutron stars are highly desired.
In this study, we investigate the interaction between quantum vortices of $^3P_2$ superfluid neutrons and flux-tubes of $^1S_0$ superconducting protons in the outer core of neutron stars, based on a successful bosonic theory of superfluid, the Gross-Pitaevskii equation (GPE). In this talk, we will discuss how the $^3P_2$ superfluid vortices interact with proton flux-tubes under a magnetic field.

Speaker: Tatsuhiro HATTORI (Institute of Science Tokyo)

29_09_Hattori.pdf

Thursday, January 30

9:30 AM → 10:35 AM Oral Presentation: Session 10

Convener: Dr Eiji Kido (Institute for Cosmic Ray Research, University of Tokyo)

9:30 AM Hunting origins of ultrahigh-energy cosmic rays

Clarifying origins and acceleration mechanisms of the most energetic particles in the universe has been the 100-year endeavor, being one of the most intriguing mysteries in an interdisciplinary research among astroparticle physics, high-energy physics and nuclear physics. Since ultrahigh-energy cosmic rays (UHECRs) are deflected less strongly by the Galactic and extra-galactic magnetic fields due to their enormous kinetic energies, their arrival directions would be correlated with their origins. A next-generation “astronomy” using UHECRs is hence a potentially viable probe to uncover mysteries of extremely energetic phenomena in the nearby universe. In this talk, I will give an introduction of cosmic-ray physics, detection techniques and the latest results of the two giant observatories in operation; Telescope Array experiment and Pierre Auger Observatory including their on-going upgrades. I will also discuss a possible source scenario of UHECR produced in binary neutron star mergers.

Speaker: Toshihiro Fujii (OMU)

30_01_Fujii.pdf

10:10 AM Constraints on super-heavy UHECR source model with a large-scale structure simulation

Current observations of arrival directions of ultra-high energy cosmic rays (UHECR) whose energies are above 100 EeV do not show significant anisotropy. To explain this situation, we may assume higher source density, heavier mass composition of UHECR, or stronger magnetic fields.
Recently the idea of super-heavy UHECR (r-process nuclei like uranium) has been suggested G. Farrar 2024, B.T. Zhang et al. 2024). The super-heavy UHECR may explain the non-anisotropy of UHECRs with a longer propagation distance and larger deflection by magnetic fields.
In this talk, we assume that the arrival directions of UHECRs are isotropic, and try to constrain the possible range of source density, mass composition, and strength of magnetic fields. Based on mock events calculated from a large-scale structure simulation (Millenium Run, Springel et al. 2005), we set the limits on source density and strength of magnetic fields, in the case of single-proton/iron/uranium.

Speaker: Ryo Higuchi (RIKEN)

30_02_Higuchi.pdf

10:35 AM → 11:05 AM Coffee Break

11:05 AM → 12:25 PM Oral Presentation: Session 11

Convener: Dr Eiji Kido (Institute for Cosmic Ray Research, University of Tokyo)

11:05 AM New Views on Thermonuclear Bursts

New Views on Thermonuclear Bursts

Speaker: Duncan Galloway (Monash University)

30_03_Galloway.pdf

11:45 AM Observations of long X-ray bursts

Long X-ray bursts (XRBs) are rare events, which are only <1% of ordinary XRBs.
Although long XRBs as well as ordinary XRBs are interpreted as thermonuclear
runaway on neutron stars, their fuel or ignition conditions are still open to debate.
In addition, there are some observations which indicate interactions between bursts
and accretion disks. This talk will summarize recent observations of long XRBs and
discussions about them.

Speaker: Motoko Serino (Aoyama Gakuin University)

30_04_Serino.pdf

12:25 PM → 2:00 PM Lunch

2:00 PM → 3:20 PM Oral Presentation: Session 12

Convener: Akira Dohi (RIKEN)

2:00 PM Investigation of 60Zn resonance states for X-ray burst light curve

X-ray bursts are frequently observed thermonuclear explosion events in the universe. Understanding their light curves is crucial for unveiling the properties of neutron stars. The shape of the light curve is sensitive to various nuclear reaction rates. It has been shown that the 59Cu(p,γ)60Zn and 59Cu(p,α)56Ni reaction rates have the most significant impact on the light curve. These reactions proceed via 59Cu+p resonance states in 60Zn, meaning that the spin-parity and decay branch ratios of these states must be determined. We measured the 58Ni(3He,n)60Zn reaction at RCNP and determined the spin-parity of three resonance states in 60Zn above the proton decay threshold for the first time. In this presentation, we will discuss the methodology, results, and future plans for the experiment to measure the decay branch ratios.

Speaker: Tatsuya Furuno (Osaka University)

2:40 PM Study of Photospheric Radius Expansion Bursts of SAX J1808.4−3658

Speaker: Yi Hua Lam (Zhejiang Sci-Tech University)

3:20 PM → 3:30 PM Break

3:30 PM → 4:30 PM Oral Presentation: Session 13

Convener: Akira Dohi (RIKEN)

3:30 PM Systematic study of fission process in heavy and superheavy mass regions related to r-process nucleosynthesis

Analyzing the current cosmic elemental composition opens the door to the origin of the cosmic elements. This requires a detailed analysis of the r-processes nucleosynthesis. Among them, our research is aimed at obtaining information on the fission of neutron-rich nuclei in the heavy and superheavy mass regions [1]. Fission fragments of neutron-rich nuclei in the superheavy elemental regions are thought to contribute to the r-process nucleosynthesis, and thus have a significant effect on the elemental composition of the universe. However, the fission of these neutron-rich regions is not accessible experimentally, so theoretical evaluation is important.
We have systematically calculated the mass distribution of fission fragments in the heavy and superheavy mass regions (2095 nuclei) using the dynamical model with the same conditions, and analyzed the characteristics of fission fragments.
From these extensive systematic calculations, we found that the mass distribution of fission fragments in the neutron-rich region shows certain characteristic tendencies within the dynamical model, but the systematics of the fission properties change around the “Island of Stability”, where nuclei have a strong nuclear structure. We would like to discuss, for example, how the specificity of the fission mode of Island of Stability the r-process network calculations.

[1] S. Tanaka, N. Nishimura, F. Minato, Y. Aritomo, Phys. Rev. C 108, 054607 (2023)

Speaker: Yoshihiro Aritomo (Kindai University)

3:55 PM Photon Vortex Generation and Photonuclear Reactions by Photon Vortex in Astronomical System

Photon vortices are light that carry large orbital angular momentum (OAM) in quantum level　[1]. They can be described by Laguerre-Gaussian or Bessel wavefunctions, which are waves being the eigenstates of the distinct angular momentum along their propagation direction . Unlike plane-wave photons, photon vortices interact differently with materials because their OAM changes the process where they transfer the relatively large angular momentum. In gamma-ray bursts (GRBs), photons in the keV range can become highly polarized due to strong magnetic fields.
Photon vortices can change the total angular momenta of compound nuclei transferred from the photon vortices when they interact with them. This is thought to play an important role in nucleosynthesis in the Universe. Liu et al. [2] found that the amplitudes of low multipole giant resonances become weaker when a photon vortex interacts on a nucleus with a relatively small impact parameter.
We study the process that photon vortices form when electrons have spiral motion in magnetic fields as strong as 10^{12}-10^{13} G. Our study includes effects from Landau quantization. Our results show that these vortices are likely generated in places with extremely strong fields, such as magnetars or magnetized accretion disks around black holes [3]. The present result suggests a possibility that magnetic fields in neutron stars and black holes play an important role in the interpretation of many observed phenomena. In particular, the photon vortices may be dominant in high energy region although there is no coherent structure at the macro level.
In this work, furthermore, we calculate the ratios of the photon absorption transition probabilities of photon vortices with Bessel wave to photons described by the plane wave [4]. The result shows enhancement of excitation of states with large total angular momentum by optimization of the divergence angle of the incident photon vortex in momentum space. However, the average cross section for the photon vortex turns out to be identical with that for the plane wave. Therefore, even when Bessel photons are predominantly produced in astrophysical environments, the isotopic abundances of the synthesized elements are not changed.

[1] L. Allen, et al. Phys. Rev. A 45, 8185 (1992).
[2] Z.-W, Lu, et al., Phys. Rev. Lett. 131, 202502 (2023).
[3] T. Maruyama, et al. Phys. Lett. B826. 136779 (2022).
[4] T. Maruyama, et al. Astro. J. 975, 51 (2024).

Speaker: Tomoyuki Maruyama (College of Bioresouce Sciences, Nihon university)

30_08_Maruyama.pdf

4:20 PM Closing Remark

Speaker: Tomoya Naito (RIKEN iTHEMS)

30_09_Naito.pdf