# 2021年

Nov 10th
16:30 JST (8:30 CET)
 Frédéric Chevy (LKB, ENS) TBA

TBA

Oct 15th
13:30 JST
 Guang Juan Wang (ASRC, JAEA) Novel coupled channel framework connecting quark model and lattice QCD: an investigation on near-threshold Ds states.

In this talk, I will discuss a novel framework to extract resonant states from finite-volume energy levels of lattice QCD and apply it to elucidate structures of the positive parity Ds resonant states nearby the DK and D*K thresholds. In the framework, the Hamiltonian effective field theory is extended by combining it with the quark model. The Hamiltonian contains the bare mesons from the quark model, its coupling with the threshold channels described by quark-pair-creation (QPC) model, and the channel-channel interactions induced by exchanging light mesons. A successful fit of the finite-volume energy levels of lattice QCD with the Hamiltonian model is made. The extracted masses and the predication for an additional state, Ds(2573), are well consistent with experimental measurements.

Oct 6th
14:00 JST
 Muneto Nitta (Keio University) $$^{3}P_{2}$$ Superfluids and pulsar glitches from quantum vortex networks

The interior of a neutron star is expected to be occupied by a neutron $$^{3}P_{2}$$ superfluid, which is the condensate of spin-triplet p-wave Cooper pairs of neutrons with total angular momentum $$J=2$$. This has rich topological structures in both momentum and real spaces: it is a topological superfluid and admits various topological defects such as half-quantum non-Abelian vortices, domain walls, surface topological defects, boojums, and so on. In the first part of this talk, I will give a brief review of the current status of $$^{3}P_{2}$$ superfluids. In the second part of this talk, I will explain our proposal to apply quantum vortex network in $$^{3}P_{2}$$ superfluids to explain pulsar glitches without any fine tuning parameters.

July 2nd
9:30 JST
 Lucas PLATTER (University of Tennessee) Few-body systems with a van der Waals interaction

Zero-range interactions have been successfully used to describe recombination processes of ultracold atoms with a large scattering length. The effects of a finite range can be included in this framework if the range is smaller than the scattering length. However, a lot of experimental data is also available for scattering lengths that are comparable in size to the range of the interaction. The interaction between neutral atoms can frequently be described by an interaction that has a long range van der Waals contribution, i.e. a 1/r^6 tail. For systems dominated by the van der Waals interaction it might be possible to construct a systematically improvable effective theory based that uses long range tail of the van der Waals interaction as a starting point. I will discuss a first application of this approach to the atomic Helium-4 trimer.

June 24
10:30 JST
 Kazuyuki SEKIZAWA (Tokyo Institute of Technology) Dynamics of Quantized Vortices in Superfluid Fermionic Systems: From Cold Atoms to Neutron Stars

I will present recent progress and attempts in studying non-linear dynamics in Fermionic superfluid systems. While much works have been performed for Bosonic systems, detailed studies of Fermionic systems are nascent due to computational complexity, despite its wide applicability including nuclear systems such as neutron stars. We are exploring superfluid dynamics in Fermionic systems based on a microscopic framework of Time-Dependent Density Functional Theory (TDDFT) extended for superfluid systems, called Time-Dependent Superfluid Local Density Approximation (TDSLDA) [1].

First, I will briefly show feasibility of TDSLDA in describing topological excitations in a strongly-correlated ultracold atomic system, known as the unitary Fermi gas (UFG). It has been shown that TDSLDA is capable of describing a decay cascade of a topological defect, from a domain wall to a vortex ring/line in agreement with experimental observation [2]. Further, it has been predicted that stability of the topological defects is affected by spin polarization [2]. Recently, we have extended the application to quantum turbulence in rotating UFG, where two types of decay regime, one dominated by vortex reconnections near the boundary and the other dominated by decaying Kelvin waves, have been identified [3].

Second, I will introduce effort related to studies of superfluid dynamics in the inner crust of neutron stars. Dynamics of quantized vortices play a key role in a phenomenon known as pulsar "glitch," a sudden spin-up of a rotating neutron star. It has been suggested, more than 45 years ago [4], that glitches may be caused by a catastrophic unpinning of a huge number of vortices in the neutron star crust. To unveil the origin of glitches, we have performed fully-microscopic TDSLDA simulations on dynamics of a quantized vortex in the presence of a nuclear impurity immersed in neutron superfluid [5]. From the results, we found that the interaction between a vortex and a nucleus is strongly "repulsive," at least for two typical neutron densities examined, n=0.014 and 0.031 fm^-3. This finding possesses a potential that substantially alters the picture of vortex pinning in the inner crust of neutron stars. Recent attempts and future plans will also be presented.

1. A. Bulgac, P. Magierski, and M.M. Forbes, The Unitary Fermi Gas: From Monte Carlo to Density Functionals, Lecture Notes in Physics, Vol. 836, pp. 305-373 (Springer, Heidelberg, 2012).
2. G. Wlazłowski, K. Sekizawa, M. Marchwiany, and P. Magierski, Suppressed Solitonic Cascade in Spin-Imbalanced Superfluid Fermi Gas, Phys. Rev. Lett. 120, 253002 (2018).
3. K. Kobuszewski, K. Hossain, M.M. Forbes, P. Magierski, K. Sekizawa, and G. Wlazłowski, Rotating Quantum Turbulence in the Unitary Fermi Gas, arXiv:2010.07464 (submitted to PRL, under review).
4. P.W. Anderson and N. Itoh, Pulsar glitches and restlessness as a hard superfluidity phenomenon, Nature 256, 25 (1975).
5. G. Wlazłowski, K. Sekizawa, P. Magierski, A. Bulgac, and M.M. Forbes, Vortex Pinning and Dynamics in the Neutron Star Crust, Phys. Rev. Lett. 117, 232701 (2016).
June 4
15:00 JST
 Naoyuki Itagaki (Yukawa Institute for Theoretical Physics, Kyoto University) Cluster structure comprised of shell model states

Essential role of the non-central interactions is one of the most characteristic features of our research field. For instance, the spin-orbit interaction is the key ingredient that enables to explain the observed magic numbers of 28, 50, 82, and 126. Furthermore, the tensor interaction has been found to contribute to the large binding energy of 4He, which can be treated as clusters in many nuclei. The nuclear systems thus show different features, shell aspects and cluster aspects, owing to the decisive effects of these two non-central interactions. The idea of combining the shell and cluster models has been fascinating the theoreticians for decades. Here, the big obstacle comes from the fact that the contribution of the spin-orbit interaction, quite important in the shell model, vanishes when we introduce simple alpha cluster wave functions. The spin-orbit interaction is the driving force which breaks the alpha cluster structure and restores the symmetry of the jj-coupling shell model. Consisting description of two pictures on the same footing is of special importance.

Theoretically speaking, the wave functions of the alpha cluster model indeed have some overlap with the jj-coupling shell model. If we take the small-distance-limit between the alpha clusters, the lowest configuration of the three-dimensional harmonic oscillator is described, but this is still different from the jj-coupling shell model wave function, where the spin-orbit interaction strongly acts. We have developed antisymmetrized quasi cluster model (AQCM), which allows the smooth transformation of the alpha cluster model wave functions to the jj-coupling shell model ones [1]. By adding only one parameter to the Brink-type alpha cluster model, the wave functions are continuously transformed to the jj-coupling shell model ones, which we call the transformation to the quasi clusters.

As the next step of the study, we prepare plural jj-coupling shell model wave functions. Until now, most of the clusters introduced as subsystems have been limited to the closure of the three-dimensional harmonic oscillator, such as 4He, 16O, and 40Ca. However, with the increase of mass number, the symmetry of the jj-coupling shell model gets more important, which might exist as subsystems of the nuclear structure. Such studies are easily performed using AQCM. The first example is 14C, and we discuss the possibility of two- and three-14C cluster configurations [2]. Here each 14C cluster is jj-coupling shell model wave function. We also discuss the cases of a few 8He and/or 9Li clusters [3]. Until now, the halo structure of 11Li has been extensively investigated, and it is intriguing to see how the halo neutrons outside the 9Li core play molecular-orbital motion when another 9Li cluster approaches.

1. N. Itagaki, M. Ploszajczak, and J. Cseh, Phys. Rev. C 83 014302 (2011).
2. N. Itagaki, A. V. Afanasjev, D. Ray, Phys. Rev. C 101, 034304 (2020).
3. Naoyuki Itagaki, Tokuro Fukui, Junki Tanaka, Yuma Kikuchi, Phys. Rev. C 102, 024332 (2020).
May 28
13:30 JST
 Hiro Ejiri (RCNP Osaka Univ. Osaka and CTU, Prague) Delta isobar ($$\Delta$$) contribution to neutrino nuclear response for double beta decay

Neutrino-less double beta decays (DBD) are of current interest for studying the neutrino nature (Majorana/Dirac), the absolute mass scale and others beyond the standard model. Here, the nuclear matrix elements NMEs are crucial for extracting the neutrino properties of the particle physics interests.

Axial-vector ($$\sigma\tau , J^\pi=1+,2-, 3+$$) NMEs in the large q (~ 100 MeV/c) region associated with DBD NMEs were studied for the first time by using nuclear and lepton charge-exchange reactions of the 0.4 GeV (3He,t) and the muon induced $$(\mu,\nu_\mu)$$. The obtained $$\sigma\tau$$ NMEs are found to be much smaller than the NMEs based on the QRPA model with the nucleonic $$\sigma\tau$$ correlations. These results suggest non-nucleonic $$\sigma\tau$$ effects. One of them is the coherent $$\Delta$$ isobar (quark $$\sigma\tau$$ flip) contribution, where many $$\Delta$$-particle nucleon-hole pairs affect coherently the DBD NME. This is incorporated by using the quenched axial-vector coupling of gAeff/gA~0.5-0.7 with gAeff and gA being the effective and bare coupling constants.

We note that the $$\Delta$$-DBD with $$\nu$$-exchange between 2 quarks in the $$\Delta$$ plays a important role in the 2+ state transition with the large $$\Delta$$ NME if the $$\Delta$$ probability in the initial ground state is of the order of $$10^{-2}$$.

Impact of the present work on DBD neutrino studies and weak-decay NMEs in a few nucleon system and light nuclei are discussed.

1. H. Ejiri, J. Suhonen and K. Zuber, Phys. Rep. 797 1 (2019).
2. H. Ejiri, J. Phys. G. 46 125202 (2019).
3. H. Ejiri, Frontiers in Physics 10.3389/fphys.2019.00030;2021.650421(2021)
4. H. Ejiri, Universe 2020,6,225 doi103390/universe 6120225 (2020)
May 14
11:00 JST
 Li Sheng Geng (Beihang University) Understanding of the LHCb pentaquark states as hadronic molecules, from masses, spin-parities to production yields
In 2019, the LHCb Collaboration updated their 2015 study, reporting on the discovery of three pentaquark states. In 2020, they reported on the existence of a candidate for hidden charm pentaquark states with strangeness. In this talk, we show that how all these states fit nicely into the molecular picture in a contact range effective field theory where they are bound states of D mesons and singly charmed baryons. In total, we predict the existence of 17 hidden charm pentaquark states with and without strangeness. We further propose some mechanisms in which their molecular nature can be tested either from the existence of triply charmed dibaryons or from the decays where they have been discovered.

References
1. Emergence of a complete heavy-quark spin symmetry multiplet: seven molecular pentaquarks in light of the latest LHCb analysis [1903.11560]
2. Model independent determination of the spins of the Pc(4440) and Pc(4457) from the spectroscopy of the triply charmed dibaryons [1907.11220]
3. Can discovery of hidden charm strange pentaquark states help determine the spins of Pc(4440) and Pc(4457) [2011.07935]
4. Test the nature of Pcs(4590) in the $$\Xi_b\to J/\psi\Lambda K$$ decay.
April 28
11:00 JST
 Xiaoling Cui (Chinese Academy of Science) Stability of quantum droplet against confinement and multi-component
In this talk, I will discuss the significant effects of external confinement and multi-component to the droplet formation in ultracold boson mixtures. First, I will show that confinement-induced boundary effect can destabilize the droplet towards the formation of a soliton-like bound state, and leads to an interesting phenomenon of soliton re-entrance at large particle numbers. Secondly, it is found that the droplet formation in ternary (three-component) bosons displays much richer physics than that in the binary case. In particular, the phase of "Borromean droplet" is identified, where only the ternary system can form a self-bound droplet while any binary subsystems cannot. The experimental relevance of these results will also be discussed.

References:
X. Cui, Y. Ma, Phys. Rev. Research 3, L012027 (2021);
Y. Ma, Cheng. P, X. Cui, arxiv:2102.00674.
March 25
11:00 JST
 Yifei Niu (Lanzhou University) Beyond Mean-field Description of Nuclear Weak Interaction Processes in Stars
How were the heavy elements from iron to uranimum made is one of 11 greatest unanswered questions of physics. Half of these heavy elements were made by the so-called r-process, the study of which faces two challenges: the accurate nuclear physics inputs, such as the nuclear mass and beta-decay half-lives, as well as the r-process sites, which could be the core-collapse supernova and neutron-star mergers.
In this seminar, I will introduce the self-consistent calculations for the beta-decay half-lives as inputs for the r-process study, and stellar electron-capture rates as inputs for supernova simulations. The model beyond quasiparticle random phase approximation (QRPA), which includes quasiparticle vibration coupling (QPVC) effect, is developed for the calculation of beta-decay half-lives, which greatly improves the agreement with experimental data compared to QRPA model. The interplay between isoscalar pairing and QPVC effect on beta-decay half-lives is studied. The finite-temperature RPA model is applied for the study of electron-capture rates of important nuclei for supernova simulations, and the role of forbidden transitions are addressed.
Feb. 25
14:00 JST
 Yusuke Tanimura (Tohoku University) How to visualize nuclear many-body correlations?
The many-body wave function contains an enormous amount of information since it is a complex function of as many variables as the number of particles. Therefore, it is in general difficult to make use of all the information of a wave function obtained with a theory. Recently, in the field of quantum chemistry, a method to visualize the correlations among all the electrons in a system have been developed and applied to studies of molecular structures [1].
It would be interesting to apply such a method also to nuclear structure. As the first step, we employ a simpler method than the one in Ref. [1]: we simply search for the most probable spatial configuration of nucleons, i.e., the set of coordinates that maximizes the square of the wave function. With this method, we visualize the N-body correlation of N-body system, using the full information of a many-body wave function. We apply the method to analyses of cluster correlations in light nuclei. We use wave function given by the Hartree-Fock (HF) theory. We show that the HF wave function indeed contains some alpha-cluster-like correlation.

[1] Yu Liu, Terry J. Frankcombe, and Timothy W. Schmidt, Phys. Chem. Chem. Phys. 18, 13385 (2016).
Feb. 24
14:00 JST
 Shimpei Endo (Tohoku University) Are atoms spherical?
Abstract: In nuclear physics, it is widely known that the atomic nuclei can be spontaneously deformed into various non-spherical shapes due to many-body effects of protons and neutrons. We discuss to what extent a similar deformation takes place in atoms, a system of many electrons and a central nuclei. Firstly, we numerically show that the atoms are rather spherical, in stark contrast to the nuclei: electron distribution in various atoms are found either strictly spherical or deformed only in the surface region due via the single-particle valence orbitals. This is in contrast to atomic nuclei, which can be deformed collectively. Secondly we show that the origin for this apparent difference can be elegantly explained by a qualitative model which estimates the energy change due to deformation. We find that the nature of the interaction plays an essential role for the collective deformation.

T. Naito, S. Endo, K. Hagino, Y. Tanimura, arXiv:2009.05955
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# 2020年

11 Dec
15:00 JST
 Shin Inouye (Osaka City University) Measurement of the Variation of Electron-to-Proton Mass Ratio Using Ultracold Molecules Produced from Laser-Cooled Atoms Watch

A rovibrationally pure sample of ultracold KRb molecules was used to improve the measurement on the stability of electron-to-proton mass ratio ( $$\mu = m_e/M_p$$ ). The measurement was based upon a large sensitivity coefficient of the molecular spectroscopy, which utilizes a transition between nearly degenerate pair of vibrational levels each associated with a different electronic potential. Observed limit on temporal variation of $$\mu$$ was $$\frac{1}{\mu} \frac{d\mu}{dt}=$$ (0.30±1.0)×10−14/year, which was better by a factor of five compared with the most stringent laboratory molecular limits to date.

26 Nov.
14:00 JST
 Shun Uchino (JAEA) Atomtronics
Ultracold atomic gases allow us to simulate bare essentials of complicated quantum phenomena. Recently, atomtronics, which is the cold-atom analog of electronics, has attracted attention due to experimental realization of mesoscopic and circuit systems with ultracold atomic gases. In this seminar, I will focus on mesoscopic transport phenomena realized by two-terminal experiments with ultracold atomic gases, and demonstrate that novel transport phenomena, which have yet to be discussed in other fields, can be realized with atomtronic devices.
27 Oct.
17:00 JST (9:00 CEST)
 Servaas Kokkelmans (Eindhoven University of Technology) Elastic few-body interactions in dilute Bose gases
The elastic scattering properties of three bosons at low energy enter the many-body description of ultracold Bose gases via the three-body scattering hypervolume D. We study this quantity for identical bosons that interact via a pairwise finite-range potential, and are able to cover the full regime from weak to strong two-body interactions. While universal behaviour for large two-body scattering lengths is expected, we also find universal behaviour of the real part of D in the weakly interacting regime. We use this result to make quantitative predictions for the thermodynamics and elementary excitations of an atomic Bose-Einstein condensate in the vicinity of a quantum tricritical point, including quantum droplets stabilized by effective three-body interactions. Furthermore, I will discuss a cumulant theory of the unitary Bose gas, which is able to capture prethermal and Efimovian dynamics when quenching a degenerate ultracold Bose gas to the unitary regime.
14 Oct.
14:00 JST
Online seminar via Zoomオンラインセミナー
Farewell seminars of Ying Zhang and Jinniu Hu

14:00 Ying Zhang (Tianjin University and RIKEN)

Lambda halo structure of C, B and Zr isotopes

The halo nuclei are characterized by its extended density profile far beyond the nuclear surface region [1-3]. Very much enhanced electric dipole transitions have been also observed in several halo nuclei as a unique phenomenon associated with the extended halo wave function [4]. For hypernuclei consisting nuclei and a Lambda hyperon, there is also possibility to have Lambda halo states in lighter systems [5,6]. In this work, we study the Lambda hypernuclei of C, B [7] and Zr isotopes by Hartree-Fock and Hartree-Fock-Bogoliubov model with Skyrme-type nucleon-nucleon and nucleon-hyperon interactions. The calculated binding energies agree well with the available experiment data for C and B hypernuclei. We found halo structures with extended wave function beyond the nuclear surface in the Lambda 1p-state in the light C and B isotopes. We also found the enhanced electric dipole transition between 1p- and 1s-Lambda states, which could be the evidence for this hyperon halo structure. The Lambda hyperon in the Zr isotopes which were predicted to have giant neutron halo, has more halo orbits near the threshold, such as 3s-, 2d-, and 1g-states. They are almost degenerate. Especially, the 3s-state could have even more extended wave function than that of the giant neutron halo.

[1] I. Tanihata, et al., Phys. Rev. Lett. 55, 2676 (1985).
[2] B. Jonson, Phys. Rep. 389, 1(2004).
[3] J. Meng and S. G. Zhou, J. Phys. G 42, 093101 (2015).
[4] T. Nakamura et al., Phys. Rev. Lett. 96, 252502 (2006).
[5] K. Miyagawa, H. Kamada, W. Glockle, and V. Stoks, Phys. Rev. C 51, 2905 (1995).
[6] E. Hiyama, M. Kamimura, T. Motoba, T. Yamada, and Y. Yamamoto, Phys. Rev. C 53, 2075 (1996).
[7] Y. Zhang, H. Sagawa, E. Hiyama, arXiv:2009.13196 [nucl-th]

14:45 Jinniu Hu (Nankai University and RIKEN)

The mass limit of a neutron star

The rapid progresses of the astronomical observable techniques provide not only great challenges but also many opportunities in the investigations of neutron star. In the past decade, the measurements of massive neutron stars above $$2.0M_\odot$$ successively broke through our recognition of their maximum masses. In 2019, a compact object was observed with a mass of $$2.50-2.67~M_\odot$$ by LIGO Scientific and Virgo collaborations (LVC) in GW19081. In this talk, I will show our results about properties of neutron star, including its mass, radius, tidal deformabilities, and so on with different density functional theories and ab initio methods obtained during the past year, when I visited SNP laboratory. We found these theoretical frameworks can describe various constraints of neutron star from the massive neutron star observations, the mass-radius simultaneous measurements (NICER), and gravitational wave detections. The maximum masses of neutron star, composed of pure hadron matter can be around $$2.55M_\odot$$, the dimensionless tidal deformabilities at $$1.4M_\odot$$ are less than $$800$$, and the radius of $$1.4M_\odot$$ are smaller than $$13.0$$ km.

[1] Y. Zhang, P. Liu, and J. Hu, Int. J. Mod. Phys. E, 28, 1950094 (2019)
[2] J. Hu, S. Bao, Y. Zhang, K. Nakazato, K. Sumiyoshi, and H. Shen, Prog. Theo. Exp. Phys., 2020, 043D01 (2020)
[3] C. Wang, J. Hu, Y. Zhang, and H. Shen, Astrophys. J., 897, 96 (2020).
[4] K. Huang, J. Hu, Y. Zhang, and H. Shen, Astrophys. J., in press, arXiv: 2008.04491

28 Sept.
13:00 JST
Online seminar via Zoomオンラインセミナー
 Tetsuo Hyodo (Tokyo Metropolitan University) Lambda(1405) as a hadronic molecule
Hadronic molecules are the new form of matter induced by the strong interaction. However, identification of the hadronic molecules involves several subtle difficulties such as the model dependence and the interpretation of the resonance wave function. To overcome these difficulties, we use the compositeness to characterize the internal structure of hadrons, and generalize the weak-binding relation for unstable resonances. It is quantitatively shown that the structure of the $$\Lambda(1405)$$ resonance is dominated by the molecular state of an antikaon and a nucleon.
9 September
16:00 JST
Online seminar via Zoomオンラインセミナー
We investigate the lifetime of the hypertriton as a function of the
Lambda separation energy BΛ in an effective field theory with
Lambda and deuteron degrees of freedom. We also consider the impact of
new measurements of the weak decay parameter of the Lambda. While the
sensitivity of the total width to BΛ is small, the partial widths
for decays into individual final states and the experimentally measured
ratio R=Γ3He/(Γ3Hepd) show a strong dependence. We comment on
recent measurements of hypertriton properties in heavy ion collisions.

3 September
14:00 JST
Online seminar via Zoomオンラインセミナー
 Peng Zhang (Renmin University, Beijing) Laser control of two-body processes in nuclear and cold-atom systems
In this talk I will introduce two of our recent works.

(1) Laser control of low-energy neutron-proton collisions. Recently the control of nuclear processes with strong laser  (power density 1019-1022 W/cm2) has attracted a lot of attention. In this work we study the low-energy elastic and inelastic scattering between neutron and proton in such a strong laser, and find that in such a system there can be extremely strong multi-photon absorption effect (i.e., the inverse bremsstrahlung effect). In some cases the neutron and proton may absorb  104-105 photons in one collision.  In addition, the inelastic scattering (absorption) rate can also be manipulated by the laser.

(2) Molecular electric dipole moment of alkaline-earth (like) atoms in 1S0 and 3P0 states. We study the molecule states of two alkaline-earth (like) atoms in 1S0 and 3P0 states respectively, and show that there is an inter-orbit electric transition dipole moment between two such states in spin singlet and triplet manifolds. For two 173Yb atoms the peak value of this electric dipole close to one Debye for 173Yb atoms. With such a dipole moment one can dress these two molecule states with electric-dipole transition induced by, e.g., a microwave, and form a dressed dipolar” molecule.

10 July
10:00AM JST
Online seminar via Zoomオンラインセミナー
 Chris Greene (Purdue University) Linking Efimov physics, few-fermion universality, and the 3n and 4n systems
This seminar will present our recent unpublished results [1] based on an adiabatic hyperspherical coordinate treatment of the 3-neutron and 4-neutron systems.  This study finds a totally repulsive hyperradial potential energy versus the hyperradius, which immediately and visually makes it clear that there cannot be any low energy resonance in either the 3n or the 4n system.  Our calculations utilize several state of the art nucleon-nucleon potentials, while also testing the importance of 3-body nuclear force terms, and multichannel coupling effects.  One major conclusion is that there is a 1/sqrt(E) zero-energy divergence of the 3-fermion and 4-fermion density of states, which might play a role in explaining the excess low-energy 4n events in the recent experiment by Kisamori et al.[2]  This talk will also demonstrate the linkage between the divergent low energy density of states (or Wigner-Smith time delay), the Efimov effect, and few-fermion universality.  Additional preliminary studies of some few-fermion systems occurring in ultracold atomic physics experiments will also be discussed.

[1] M. D. Higgins, C. H. Greene, A. Kievsky, and M. Viviani, arXiv:2005.04714 (2020).
[2] K. Kisamori et al., Phys. Rev. Lett. 116, 052501 (2016)

22 June
14:00
Online seminar via Zoomオンラインセミナー
 Munekazu Horikoshi (Osaka City University) Ultracold AMO experiment for quantum few-body and many-body
Ultracold atomic gases can mimic various quantum systems due to their characteristic of short range interactions, dilute density, and tunable interactions using Feshbach resonances. Since they basically show the universal physics which does not depend on detail of particle and the absolute energy scale, we can simulate various quantum systems experimentally, namely quantum simulation. In this seminar, I will introduce recent our cold atom experiments using lithium atoms from basic of the cold atomic system to application to the neutron star equation of state. Also I will show you our recent study toward studying quantum many-body cluster physics.

27 May
16:00
Online seminar via Teamsオンラインセミナー
 Yuta Sekino (RIKEN) Mesoscopic spin transport between strongly interacting Fermi gases
Ultracold atomic gases are pure and highly controllable systems, providing us an ideal platform to examine physical properties of quantum many-body systems with strong interparticle interactions.

In this talk, we report our theoretical study on mesoscopic spin transport for strongly interacting Fermi gases through a quantum point contact [1], which can be realized in ultracold atom experiments. By employing the linear response theory and many-body T-matrix approximation, we investigate how a strong interaction affects the spin current. For a small spin-bias regime, the current in the vicinity of the superfluid transition temperature is strongly suppressed due to the formation of pseudogaps, which are dip structures in single-particle densities of states. For a large spin-bias regime where the gases become highly polarized, on the other hand, the current is enhanced by the appearance of Fermi polarons, which are quasiparticles consisting of minority atoms dressed by majority atoms. These results suggest that the spin transport measurement in our setup becomes a novel probe to examine pseudogap and polaronic phenomena in ultracold atom experiments.

[1] Y. Sekino, H. Tajima, and S. Uchino, Phys. Rev. Research 2, 023152 (2020)

# 2019年

24 May
14:00
RIKEN Main Research Building, room 213
Shoichi Sasaki (Tohoku University)
Nucleon form factors from lattice QCD at the physical point
The nucleon vector and axial elastic form factors are good probes to investigate the internal structure of the nucleon. Although great theoretical and experimental efforts have been devoted to improving our knowledge of the nucleon structure, there are several unsolved problems associated with fundamental properties of the proton and neutron. The proton radius puzzle, where high-precision measurements of the proton's electric charge radius from the muonic hydrogen ($(J\mu H$) Lamb shift disagree with well established(B results of both electron-proton scattering and hydrogen spectroscopy, is currently one of the most intriguing problems in this field. The neutron lifetime puzzle, where the discrepancy between the results of beam experiments and storage experiments remains unsolved, is another open question that deserves further investigation in terms of the nucleon axial-vector coupling ($g_A$).
In this talk, we report our recent results of the nucleon iso-vector form factors measured on a large-volume lattice $(10.8~{(J\rm fm})^4$  at the physical point in 2+1(B flavor QCD. The configurations are generated with the stout-smeared $O(a)$ improved Wilson quark action and Iwasaki gauge action at $(J\beta=6/g^2=1.82$,(B which corresponds to the lattice spacing of 0.085 fm. The pion mass at the simulation point is about 135 MeV. A large spatial volume of $(10.8~{(J\rm fm})^3$(B allows us to investigate the form factors at small momentum transfer region.
We obtain the electric and magnetic form factors and their RMS radii which are evaluated from the slope of the respective form factor at the zero momentum transfer. We find that our results for the electric RMS charge radius seem to favor the experimental result of the $(J\mu H$ spectroscopy within 1-sigma(B error, though it is still too early to draw any definitive conclusion. We also obtain the axial-vector coupling and the axial RMS radius from the axial-vector form factor. Although the 2% precision of our $g_A$ value is an order-of-magnitude larger than the experimental one, our result of the axial RMS radius that achieves the 7% precision is comparable with the experimental one.

# 2018年

3 Dec.
14:00
RIKEN Main Research Building, room 224&226
GuangJuan Wang (Peking University)
The strong decay patterns of Zc and Zb states in the relativized quark model
In this talk, I will talk about the strong decay patterns of the Zc and Zb states. They are assumed to be hadronic molecules composed of open-flavor heavy mesons.

Employing the relativized quark model and the quark-interchange model, we investigate the charged heavy quarkonium-like states Zc(3900), Zc(4020), Zc (4430), Zb(10610) and Zb(10650) decaying into the ground and radially excited heavy quarkonia via emitting a pion meson. The calculated decay ratios can be compared with the experimental data, which are useful in judging whether the molecule state assignment for the corresponding Zc and Zb state is reasonable or not. The theoretical framework constructed in this work will be helpful in revealing the underlying structures of some exotic hadrons.
20 Nov.
14:00
RIKEN Main Research Building, room 213
Huseyin Bahtiyar (Mimar Sinan Fine Arts University, Istanbul, Turkey )
Radiative transitions of singly- and doubly-charmed baryons in lattice QCD
In this talk, I will summarize our recent results from radiative transitions of singly- and doubly-charmed baryons in lattice QCD.

I will summarize the spin-3/2 to spin-1/2 electromagnetic transitions of the Omega_cc, Xi_cc and Omega_c baryons as well as the spin-1/2 to spin-1/2 transitions of Xi_c and Xi_c^prime baryons studied on 2+1 flavor lattices with a pion mass of ~156 MeV.

In these works, we extracted the transition form factors and computed the decay widths and lifetimes of spin-3/2 Xi_cc, Omega_cc and Omega_c baryons and spin-1/2 Xi_c^prime baryon.

We also used two different heavy-quark actions to study the discretization effects. A comparison has ben made between two actions in the case of the Omega_c baryon.
11 Oct.
13:30
RIKEN Main Research Building, room 224&226
Michele Viviani (INFN Pisa & Department of Physics, University of Pisa)
Theoretical study of three and four neutron resonances
Recently, the interest on establishing the existence of low energy three and four neutron resonances has been renewed. The possible existence of a four neutron resonance has been recently reported experimentally, but different theoretical groups find conflicting solutions on that problem. In this talk, this issue is studied solving the 3n→3n and 4n→4n scattering problems using the adiabatic Hyperspherical Harmonic approach. The preliminary results of this investigation will be shown and discussed.
7/25
11:00
RIKEN Main Research Building, room 224&226
Yuki Kamiya (Yukawa Institute for Theoretical Physics, Kyoto University)
Model-independent determination of structure of exotic hadrons with the scattering amplitude
Understanding of the internal structure of exotic hadrons is an important topic of the current hadron physics. Particularly in recent years, precise data on the hadron scattering have been accumulated from the experimental analysis, and it is becoming possible to extract detailed information on the scattering amplitude. This enables us to study the hadron structure from the properties of the scattering amplitude.

In this seminar, the model-independent approaches to study the hadron structure from the scattering amplitude are discussed. In the first part, the weak-binding relation between the experimental observables and compositeness, defined as the probability of finding the composite component, is introduced [1, 2]. While the compositeness is in general model-dependent quantity, this can be calculated in a model-independent manner using the experimental observables when the hadron is weakly-binding s-wave state. Here, I mainly explain the reasoning of small model dependence of the compositeness in the weak-binding limit. In the second part, we see the qualitative method using the position of the Castillejo-Dalitz-Dyson (CDD) zero defined as the zero of the amplitude [3]. For the eigenstate that originates in the hidden channel, the existence of the CDD zero close to the pole is indicated by the topological nature of the phase of the amplitude. At the end of each part, the applications to Lambda(1405) baryon are discussed.

[1] S. Weinberg, Phys. Rev. 137, B672 (1965).
[2] Y. Kamiya and T. Hyodo, Phys. Rev. C 93, 035203 (2016), Y. Kamiya
and T. Hyodo, Prog. Theor. Exp. Phys. (2017) 023D02.
[3] Y. Kamiya and T. Hyodo, Phys. Rev. D 97, 054019 (2018).
6/20
15:00
RIKEN Main Research Building, room 435&437
Nodoka Yamanaka (Institut de Physique Nucléaire Orsay (IPN Orsay))
The AFTER project, and the gluon and charm content of the deuteron
Fixed-target experiments using the high energy beam of the LHC can unveil various aspects of quantum chromodynamics (QCD) thanks to the ALICE and LHCb detectors, the high luminosity typical of high energy accelerators, and the versatility of the target with the possibility to polarize it. One of the most important topics to be studied is the nucleon structure when the constituents (partons) have a high momentum fraction. In the first part of this seminar, we will present the experimental project of A Fixed Target ExpeRiment (AFTER@LHC) [1], with an emphasis on the precise determination of the parton distribution functions (PDFs) of nucleons and nuclei.

In the second part, we will report on the gluon and charm PDFs of the deuteron using light-front quantization together with the impulse approximation [2]. We use a nuclear wave function obtained by solving the nonrelativistic Schrödinger equation using the Gaussian expansion method [3] with the realistic Argonne v18 nuclear force; it is then convoluted with the proton PDF. As a result, we found that the gluon distribution in the deuteron (per nucleon) is smaller than that of the proton by a few percent close to x = 0.4, whereas it is enhanced at x larger than 0.6. We will discuss the applicability of our computation and will comment on how to extend it to x as large as two. We will also present the charm distribution of the deuteron within the same approach by considering perturbatively and non-perturbatively (intrinsic) generated charm inside the deuteron. In particular, we note that the intrinsic charm content in the deuteron may be enhanced for 6-quark configurations.

[1] S. J. Brodsky, F. Fleuret, C. Hadjidakis, and J.-P. Lansberg, Phys. Rep. 522, 239 (2013).
[2] S. J. Brodsky, K.Y.J. Chiu, J.P. Lansberg, NY, arXiv:1805.03173 [hep-ph].
[3] E. Hiyama, Y. Kino, and M. Kamimura, Prog. Part. Nucl. Phys. 51, 223 (2003).
6/18
13:30
RIKEN Main Research Building, room 224&226
Yusuke Namekawa (Institute of Physics, University of Tsukuba)
Successful prediction to charmed single hadrons and attempt on two-hadron by lattice QCD
I will present our results of charmed hadrons, with emphasis on our successful prediction to the doubly charmed baryon Ξcc . I also explain our new attempt on two-hadron interaction by lattice QCD.
5/17
13:30
RIKEN Main Research Building, room 224&226
Yoshiko Kanada-En'yo (Department of Physics, Kyoto University)
Isoscalar monopole and dipole excitations in light nuclei
The low-energy dipole excitations in neutron-rich nuclei are attracting a great interest in physics of unstable nuclei. A particular attention is paid on isoscalar and isovector natures of dipole excitations. We studied dipole excitations in Be isotopes with an extended version of the antisymmetrized molecular dynamics, which are designed to describe 1p-1h excitations and large amplitude cluster modes. Two dipole modes were obtained in the low-energy dipole excitations in 10Be. In this talk, I will briefly overview our recent researches on nuclear clustering, and then discuss the dipole excitations in light nuclei.
2/21
14:30
RIKEN Main Research Building, room 224&226
Michio Kohno (Research Center for Nuclear Physics, Osaka University)
Hyperons in nuclear matter from YN and YNN interactions in ChEFT and hyperon puzzle
In ordinary nuclei, chiral NN and NNN interactions in chiral effective field theory (ChEFT) are now standard for ab initio studies. The description of baryon-baryon interactions in the strangeness sector has also been developed. After a brief introduction to the construction of baryon-baryon interactions in ChEFT, hyperon single-particle potentials calculated in nuclear matter with NLO hyperon-nucleon (YN) and NNLO hyperon-nucleon-nucleon (YNN) interactions parametrized in ChEFT are presented. The NLO YN interactions bear strong lambda-sigma coupling. The interesting result is that the lambda potential becomes shallower beyond the normal density. Together with the repulsion from the YNN interactions, the ChEFT description provides the possibility to solve the hyperon puzzle without introducing ad hoc assumptions.
2/20
16:00
RIKEN Main Research Building, room 224&226
M. Tachikawa (Graduate School of Nanobioscience, Yokohama City University)
Ab initio calculation for positronic compounds
We have extended the conventional ab initio methods, such as molecular orbital and quantum Monte Carlo methods, to the multi-component systems, which composed of electrons, a positron, and nuclei. We have carried out the accurate calculation of positron affinity and pair annihilation rate for positronic compounds by using these multi-component methods including vibrational effect, and found that these values are in reasonable agreement with the corresponding experimental ones. [1-4] The positronic orbital is much more delocalized than the highest occupied electronic orbital, and the correlation between positron affinity and both permanent dipole moment and dipole-polarizability is clearly shown.
[1] M. Tachikawa, Y. Kita, and R. J. Buenker: Phys. Chem. Chem. Phys. 13 (2011) 2701.
[2] M. Tachikawa, Y. Kita, and R. J. Buenker: New J. Phys. 14 (2012) 035004.
[3] Y. Yamada, Y. Kita, M. Tachikawa: Phys. Rev. A 89 (2014) 062711.
[4] K. Suzuki, T. Takayanagi, Y. Kita, M. Tachikawa, and T. Oyamada: Comp. Theo. Chem. 1123 (2018) 135.

# 2017年

9/15
15:00
RIKEN Main Research Building, room 224&226
Hyeon-Deuk Kim (Kyoto University)
Quantum Molecular Dynamics Simulation Method for Hydrogen Molecules -From a Small Molecule to Condensed Phases-
Nuclear quantum effects of hydrogen nuclei such as zero-point energy and nuclear delocalization significantly influence dynamical and structural properties of condensed hydrogen systems. I will report the first computational study on real-time dynamics of hydrogen molecular liquids, solids, and supercooled liquids exhibiting strong nuclear quantum effects which have been hardly accessible by use of previous computational and theoretical methods like density functional theory and semiquantum molecular dynamics simulations with path integrals. [1-6] All the physical insights and information we obtained will provide a milestone for identifying and characterizing various unknown hydrogen phases, which will open a new avenue of hydrogen material research.

[1] K. Abe and K. Hyeon-Deuk, J. Phys. Chem. Lett., 8, 3595 (2017)
[2] K. Hyeon-Deuk, and K. Ando, Phys. Chem. Chem. Phys. (Communication), 18, 2314 (2016)
[3] K. Hyeon-Deuk, and K. Ando, J. Chem. Phys. (Communication), 143, 171102 (2015)
[4] K. Hyeon-Deuk, and K. Ando, Phys. Rev. B, 90, 165132 (2014)
[5] K. Hyeon-Deuk, and K. Ando, J. Chem. Phys. (Communication), 140, 171101 (2014)
[6] K. Hyeon-Deuk, and K. Ando, Chem. Phys. Lett., 532, 124 (2012)
7/5
15:00
RIKEN Main Research Building, room 224&226
Kenji Sasaki (YITP, Kyoto University)
Lattice QCD study on baryon-baryon interactions
The baryon-baryon (BB) interaction is one of the central topics in hadron and nuclear physics. Especially for the strangeness sector, in spite of lack of experimental data, detailed properties of it is required to understand the hypernuclear structures and deep inside of neutron stars. We investigate BB interactions via the time-dependent HAL QCD method which enables us to derive potentials from Nambu-Bethe-Salpeter (NBS) wave function simulated on the lattice. We report the latest results of BB potentials and their scattering observables especially focusing on the strangeness S=-2 sector. We also discuss the possibility of H-dibaryon state through the Lambda-Lambda and N-Xi scatterings.
7/5
13:30
RIKEN Main Research Building, room 224&226
Takaya Miyamoto (YITP, Kyoto University)
Lambda_c N interaction from lattice QCD and its application to Lambda_c hypernuclei
We study the Lambda_c - nucleon interaction faithful to S-matrix in QCD on the basis of the HAL QCD method. In HAL QCD method, Nambu-Bethe-Salpeter wave functions are calculated on the lattice, and potentials are extracted form them. I will present our results on the 1S0 and 3S1 Lambda_c - nucleon potentials and scattering observables such as phase shifts. The scattering observables show that the Lambda_c - nucleon interaction is attractive and its spin dependence is weak. Using the extracted potentials, we also examine possible Lambda_c nuclei by constructing a single-folding potential, which can be studied at J-PARC and FAIR in the future.
6/16
15:00
RIKEN Main Research Building, room 224&226
Mitsunori Fukuda (Osaka University)
Study of surface structure of nuclei via reaction cross sections
We have been developing a method to deduce proton-, neutron-, and nucleon-density distributions in a nucleus via the reaction cross section that stands for a possibility of nuclear collision. Using this prescription, we can now discuss halo- and skin-structures, or nuclear deformations based on the experimental reaction cross section data. In this talk, I would like to show recent results of experiments at NIRS-HIMAC* and RIKEN. Especially, the latest preliminary result from the experiment carried out at RIBF last autumn on Ca and Ni isotopes will be introduced to discuss neutron-skin thickness and the equation of state for asymmetric nuclear matter.
5/29
13:30
RIKEN Main Research Building, room 224&226
Yudai Suwa (YITP, Kyoto University)
Formation of Neutron Stars
A core-collapse supernova is a generation site of a neutron star as well as one of the largest explosions in the universe. In this talk, I will show our recent results of supernova simulations with multi-dimensional neutrino-radiation hydrodynamics, especially focusing on neutron star formations.
4/18
15:00
RIKEN Main Research Building, room 224
Ulugbek Yakhshiev (Inha University)
Topological models and their applications
In this talk some examples of the applications of instantons and skyrmions in describing the properties of strongly interacting systems will be discussed. In particular, first we discuss the contributions of nonperturbative effects in the heavy quark sector starting from the instanton induces quark-antiquark potential. The second, we start from the effective skyrmion-skyrmion interactions in a many body systems and discuss the properties of the many-nucleonic systems.

4/18
13:30
RIKEN Main Research Building, room 224
Hyun-Chul Kim (Inha University)
Heavy Baryons and excited baryons in the pion mean fields
An ordinary heavy baryon consists of one heavy quark and two light quarks.
In the present seminar, we review a recent work on the mass splitting of the lowest-lying heavy baryons, based on the chiral quark-soliton model. The dynamical variables were fixed in the light-baryon sector, the experimental data being used. The results were in remarkable agreement with the experimental data. We also predict the mass of the Omega_b.  Within the same framework, we also analyze recent experimental results for excited Omega_c from the LHCb experiment. We suggest possible scenarios on them.
As a second part of the talk, we will discuss a recent study on excited baryons, based on the extended chiral quark-soliton model. Since the confinement plays an essential role in describing the excited baryons, we consider the confining background field in addition to the pion mean field. To avoid the divergence in the quark level, we chop off the linearly-rising confining field at a certain value that is comparable to the quark mass. We discuss the mass spectra of the first excited baryons. We also discuss the theoretical puzzles on the mass ordering of N*(1440) and N*(1535) as well as N*(1535) and N*(1520).

3/28
15:00
RIKEN main Research Building, room 224
Rimantas Lazauskas (Université de Strasbourg, Flance)
On the possible existence of 4n resonances
I will discuss about the possibility for a four neutron system to posses a narrow resonance as suggested by a recent experimental result in RIKEN. Before discussing my own development, a short overview of the experimental and theoretical results concerning pure neutron systems will be presented.
Since any sensitive modification of the nucleon-nucleon (NN) potentials or on the leading contributions of the three-nucelon (NNN) forces affect strongly the nuclear chart, in our recent work we have introduced a phenomenological T = 3/2 three neutron force, in addition to a realistic NN interaction, as an artefact to accommodate a 4n nearthreshold states. We inquired what would be the strength of such a 3n force in order to generate a resonance compatible with the experimental findings. The reliability of the resulting three-neutron force in the T = 3/2 channel is examined, by analyzing its consistency with the low-lying T = 1 states of 4H, 4He and 4Li and the 3H + n scattering. Two independent configuration space methods are used in solving the four-body problem: the Gaussian expansion method to solve the Schrodinger equation and the Lagrangemesh technique applied to solve the Fadeev-Yakubowsky equation. The boundary conditions related to the four-body problem in the continuum are implemented by using the complex scaling method and the position of the 4n resonances in the complex energy-plane are determined.
3/27
13:30
RIKEN main Research Building, room 224
Rimantas Lazauskas (Université de Strasbourg, Flance)
Some developments in few-particle scattering problem based on complex-scaling method
The solution of the scattering problem in configuration space is a very difficult task both from formal (theoretical) as well as from computational points of view. The principal difficulties are related with the complex structure of the systems wave function in the asymptotes, being result of either presence of multiple scattering channels or the systems breakup into three or more clusters. One is obliged to seek for the exact methods enabling to treat the multiparticle scattering problem by avoiding the explicit treatment of the systems wave-function at the boundaries.
Complex-scaling method, proposed in the late sixties by Nuttal and Cohen, offers very accurate and elegant formalism to treat diverse scattering problems for short range potentials. Within the last few-years I have applied this method in handling very different scattering problems: 2-body collisions including Coulomb interaction, Optical potentials; scattering including the 3-body break-up for real and Optical short-ranged interactions; 3-body and 4-body scattering for the systems, where two-particles (clusters) are charged; 3-body break-up amplitude for n-d as well as p-d scattering. Finally, I have demonstrated that the conventional smooth complex scaling technique might be also used in describing collisions in pure Coulombic 3-body systems. These recent achievements will be overviewed and discussed.

# 2016年

11/11
13:00
RIKEN main Research Building, room 124&126
Francisco Miguel MARQUÉS MORENO (LPC (ENSICAEN), France)
The neutron as a building block of nuclei
Neutrons decay into a proton after several minutes, and they can only escape their fate inside nuclei with the help of other protons. Do they really need protons to survive? Experimental programs try to provide a final answer to this question since the 1960s, but forming a nucleus with neutrons only is not an easy task, even theoretically! We will pass in review the different techniques that have been used, discuss a few key issues about the subject of neutral nuclei, and describe the present and future plans that should answer this question at RIKEN.

11/07
14:00
RIKEN main Research Building, room 213
Emiko Hiyama (RIKEN, Japan)
Structure of the four-body tetra neutron
10/03
13:30
RIKEN main Research Building, room 424&426
Roman Skibinski (Jagiellonian University, Poland)
Recently developed two-nucleon interactions applied to three-nucleon systems
In recent years the family of nucleon-nucleon interactions has been expanded by new models arising from different assumptions and motivations.
In this talk I will focus on such forces as the improved chiral interaction of the Bochum-Bonn group, the JISP16 force and low-momentum interaction arising from the CD-Bonn force via the unitary transformation. While all models describe two-nucleon systems very well, their behaviour changes when applied to three-nucleon reactions. I will briefly overview applications of this forces to elastic nucleon-deuteron scattering and/or weak muon capture processes at energies below the pion production threshold.

08/01
13:30
RIKEN main Research Building, room 424&426
Qiang Zhao (Institute of High Energy Physics, Chinese Academy of Sciences)
Understanding the shortened lifetime of hypertriton
We study the mechanism for the hypertriton hadronic weak decay and provide an explanation for its significantly shortened lifetime which was observed recently by GSI, ALICE and STAR.

06/15
13:30
RIKEN main Research Building, room 213
Jirina Stone (University of Tennessee)
Low energy nuclear structure modeling; Can it be improved?
Enormous effort of generations of physicists has been devoted to understanding low energy nuclear structure since the discovery of the atomic nucleus in 1911. Properties of nuclei in their ground state, including their mass, building energy and shape provide a vital input to many areas of sub-atomic physics as well as astrophysics and cosmology. Low energy excited states are equally important for understanding nuclear dynamics. Yet, no consensun exis as to what is the best path to a theory, which would not only consistently reproduce a wide variety of experimental data but also have enough predictive power to yield credible predictions in area where data are still missing.
In this talk I will give a basic outline of some of the main obstacles preventing us building such a theory. These include the change between the nucleon-nucleon force in free space and in nuclear environment, the saturation property of the nuclear force and effects of the sub-nucleon (quark) structure of the nucleon. Selected classes of nuclear models, shell models, mean field models, microscopic-microscopic and ab-initio models, will be discussed with emphasis on their regions of applicability. Finally, suggestions will be made for, at least partial, progress that can be made with the quark-meson coupling model, as reported in the recent publication.

05/20
13:00
RIKEN main Research Building, room 424&426
Shin Watanabe (RIKEN)
Dynamic properties of 6Li elastic scattering
We investigate four-body breakup dynamics of 6Li elastic scattering on heavy targets (n+p+α+T; T=target). Since the n+p subsystem of 6Li has a bound state as deuteron (d),
there exist not only four-body breakup processes (6Li+T→n+p+α+T) but also three-body breakup processes (6Li+T→d+α+T).
This makes reaction dynamics more complex in 6Li scattering than in scattering of Borromean systems such as 6He (n+n+α+T).
In order to take into account both the breakup processes explicitly,
6Li is constructed by the Gaussian expansion method and the scattering process is then described with the four-body version of continuum-discretized coupled-channels method (four-body CDCC).
Four-body CDCC reproduces measured elastic cross sections without introducing any adjustable parameter.
In this seminar, we will discuss which of four- and three-body breakup processes is favored in 6Li scattering and clarify the dynamic properties of 6Li scattering.

05/20
11:00
RIKEN main Research Building, room 424&426
Tingting Sun (Zhengzhou University, Peking University)
Relativistic mean field approaches for Xi^- hypernuclei and current experimental data
Motivated by the recently observed hypernucleus (Kiso event) Xi15C (14N+Xi^-),
we identify the state of this system theoretically within the framework of the
relativistic-mean-field model. The XiN interactions are constructed to reproduce
the two possibly observed \Xi^- removal energies,
4.38\pm 0.25 MeV or 1.11\pm 0.25 MeV.
The preferred interpretation of the event is 14N(g.s.)+Xi^-(1p),
which is consistent with previous data on the hypernucleus Xi12Be (11B+Xi^-).

01/06
16:00
RIKEN main building, room 424
Ulugbek Yakhshiev (Inha University)
From nucleons to nucleonic systems (Chiral soliton approach)
We discuss the structure of the nucleon in free space and its structure changes in nuclear environment in the framework of in-medium modified chiral soliton model. The influence of surrounding nuclear environment to the in-medium nucleon properties is taken into account by means of the pion-nucleus optic potential in the mesonic sector. The parameters of the optic potential are related to the pionic atoms data at low densities and to the nuclear matter matter properties at the saturation density. Then the properties of symmetric and asymmetric nuclear matter are discussed. Further, considering the extrapolations to extreme high densities, the structure and properties of neutron stars are also discussed.

# 2015年

12/18
14:00
RIKEN main building, room 224
Kenta Miyahara (Kyoto University)
Weak decays of charmed baryons for the study of strange baryon resonances
Recently, three-body decays of the ground state charmed baryons like Lambda_c and Xi_c have been measured by Belle and BESIII collaborations. These decays lead to the analysis of interesting baryon resonances with strangeness such as Lambda(1405) and Xi(1690) through the final state interaction of the meson-baryon pair. In this work, we study the weak decay processes theoretically, and find that these are ideal to analyze the properties of resonances. For instance, these decays can filter the isospin of the meson-baryon pair and provide clear resonance signal compared with other production reactions. With the decay processes, we calculate the spectra of Lambda and Xi resonances and conclude that these decays are quite useful to clarify the nature of the baryon resonances with strangeness S=-1 and -2.

11/20
14:00
RIKEN main building, room 224
Takuma Yamashita (Tohoku University)
Weakly binding system of positronic alkali atom: relativistic effects and resonance states
Positron (e+), an anti-particle of an electron, can be bound to some kinds of atoms and forms positronic atoms. Since the positron has the same but an opposite sign of charge, the positron lies far away from the nucleus by Coulombic repulsion. A positron and an electron form a hydrogen-like bound state which is called a positronium (Ps). Because of the same mass as an electron, the wavefunction of the positron spreads widely. Positron can be an alternative and a unique probe to electronic states of atoms/molecules by analyzing annihilation gamma rays. Recently, a low energy and high resolution positron beam has been developed, and the search for resonance states of positronic noble gas atoms is becoming possible [1]. Since the positronic atoms are expected to show many different faces from ordinary atoms, many theoretical and experimental attempts have been made to open a new aspect of atomic physics.
Positronic alkali atoms (APs+) have a minimum necessary to describe the positronic and electronic states of positronic atoms and have been the best testing grounds. We can regard the alkali atom (A) as a two-body model consisting of a valence electron and residual closed-shell ion core (A+). Both positron-valence electron active correlation and polarization of the ion core/atom can be described effectively. Since the ionization energy of an alkali atom is smaller than that of a Ps, the structure of the loosely bound state of APs+ shows Ps cloud which exists as Ps halo [2].
In this work, we precisely calculate bound and resonance states of LiPs+, NaPs+, KPs+, RbPs+ and CsPs+ as a three-body system {A+, e-, e+} with a Gaussian Expansion Method, and find unique and exotic features of positronic alkali atoms. Relativistic effects based on the Breit-Pauli interactions to loosely bound states of LiPs+ and NaPs+ are investigated [3] by comparing with normal atoms. Structures and mechanisms of resonance states caused by weak long-range forces are also investigated.

[1] J. R. Machacek, R. Boadle, S. J. Buckman, and J. P. Sullivan, Phys. Rev. Lett. 86, 064702 (2012).
[2] J. Mitroy, Phys. Rev. Lett. 94, 033402 (2005).
[3] T. Yamashita, and Y. Kino, J. Phys. Conf. Ser., 635, 052086 (2015).

11/12
14:00
RIKEN main building, room 224
Doerte Blume (Washington State University)
The helium Efimov trimer and larger bosonic droplets
The quantum mechanical three-body problem has been studied extensively for about a century. The helium atom (two electrons and a nuclues) and the molecular hydrogen ion (two protons and one electron) are textbook examples that illustrate the organization of the periodic table and molecular binding mechanisms, respectively. In 1970 Vitaly Efimov predicted a rather different and counterintuive quantum mechanical three-body binding mechanism that leads to an infinite series of stable three-body states of enormous spatial extents. These Efimov states are predicted to exist for short-range interactions like the van der Waals force between atoms or the strong force between nucleons. When the potential becomes so shallow that the last two-body bound state is at the verge of becoming unbound or is unbound, then three particles stick together to form Efimov states. This talk will review recent theoretical and experimental advances in this field. The observation of the helium trimer (three neutral helium atoms) Efimov state and extensions of the Efimov scenario to four- and higher-body systems will be discussed.

10/19
13:00
RIKEN main building, room 424

「メタマテリアル」は，電磁波の波長より小さな構造を用いて物質の電磁気学特性を操作した人工物質である．メタマテリアルは，マイクロ波から光波まで幅広い周波数領域で研究されているが，我々は特に光の領域で動作する「光メタマテリアル」の実現とその応用展開を目指して研究を進めている．これまで我々は，この光メタマテリアルを作るために必要な加工技術を中心に，レーザーを用いたトップダウン的な手法や，DNAや磁場を用いたボトムアップ的な手段，さらに最近では，トップダウンとボトムアップを融合させた新しい手法を開発・提案してきた．講演では，これらの内容とともに，メタマテリアルのサイエンスとテクノロジーについて紹介する．

10/19
11:00
RIKEN main building, room 424
Carlo Barbieri (University of Surrey, UK)
Medium-mass isotopes from three-nucleon chiral interactions and Lattice QCD forces
The seminar will review two related developments in the ab-initio study
of medium-mass exotic nuclei. The self-consistent Green’s function theory
method is used to learn about the characteristics of single nucleon
correlations along several full spectroscopic chains.

In the first case, chiral EFT interactions have been used to obtain
the nuclear spectral function of the oxygen isotopes. This confirmed
from the ab-initio perspective the mechanism by which three nucleon
forces generate the anomalous dripline at O24 and also affect nearby
fluorine isotopes.  We will also discuss implication of 3NFs for the
Ca chain and its neighbours. Very neutron rich Ca and K isotopes have
recently been measured and suggest the necessity for improved chiral
interactions.

In the second part, we will discuss the structure of closed shell
isotopes as generated by nuclear forces from Lattice QCD simulations.
For pion mass of 470 MeV (now getting closer to the physics limit)
4He and 40Ca are finally bound. However, the 16O could be still
unstable under breakup onto four alpha particles.

7/27
14:00
RIKEN main building, room 224
Petr Vesely (Nuclear Physics Institute, Czech)
Hypernuclear Spectra within Mean Field and Beyond Mean Field Approach
In the first part of talk I will introduce the calculations of (ordinary) nuclei based on the self-consistent HFB method, solved with the realistic NN interactions, and subsequent Equation of Motion Phonon Model (EMPM). The EMPM model is used for the calculations of the excitation spectra within multi particle-hole configuration space. Such configurations are important to incorporate the beyond mean field correlations into the description of nuclear spectra.
In the second part of the talk I will speak about the modification of this model which allows to describe the spectra of medium and heavy hypernuclei.

7/22
14:30
RIKEN main building, room 424
Kei Yamamoto (山本恵) (KEK)
Probing high scale SUSY in low energy FCNC
Heavy flavor physics has played an essential role in testing the CKM paradigm of the Standard Model and in searching for new physics. CP violation and rare decays of K and B meson and EDM can be good probe for new physics such as supersymmetry.
In our work, taking account of the recent LHC results for the Higgs discovery and the SUSY searches we consider the high-scale SUSY scenario in the framework of the non-minimal flavor violation. We discuss the effect of the high scale SUSY on FCNC of K, B0 and Bs mesons.

References:
M. Tanimoto and K. Yamamoto, "Sensitivity of High-Scale SUSY in Low Energy Hadronic FCNC”, Symmetry 7 (2015) 689 [arXiv:1506.01850 [hep-ph]].
M.Tanimoto and K.Yamamoto, "Probing the high scale SUSY in CP violations of K, B0 and Bs mesons",  Phys. Lett. B 735 (2014) 426 [arXiv:1404.0520 [hep-ph]].

6/22
15:00
RIKEN main building, room 424
Tomoya Murata (村田知也) (Osaka University)
Neutrino induced 4He break up reaction
The neutrino-nucleus reactions play an important role for the heating and cooling mechanism in the core collapse supernova explosion. In addition to neutrons, protons and one representative nuclei line iron, 4He has been considered in the equation of state of supernovae. In ref. [1], light nuclei such as deuteron, triton and 3He are taken into account. 4He has been considered as a significant component and the importance of neutrino-4He reactions has been studied in the accelerating shockwave [2] and nucleosynthesis [3]. The neutrino-4He reaction cross sections are evaluated in shell-model approach[4] and an approach using Lorentz Integral Transformation method [5].

In this presentation, we will report on our analysis of cross sections and temperature averaged cross sections for CC and NC (anti-)neutrino induced 4He break up reactions:

νe + 4He → e- + X(A=4, Z=3)
\bar{νe} + 4He → e- + X(A=4, Z=1)
νe / \bar{νe} + 4He → νe / \bar{νe} + X(A=4, Z=2).

For this analysis, we have employed the spin-dipole and dipole strength functions of 4He calculated in the Complex Scaling Method (CSM) [6]. Comparison with the previous works will be discussed.

[1] K. Sumiyoshi and G. Ropke, Phys. Rev. C77, 055804 (2008).
[2] W. C. Haxton, Phys. Rev. Lett. 60, 1999 (1988).
[3] G. M. Fuller and B. S. Meyer, Astrophys. J. 453, 792 (1995).
[4] T. Suzuki, S. Chiba, T. Yoshida, T. Kajino and T. Otsuka, Phys. Rev. C74, 034307 (2006).
[5] D. Gazit and N. Barnea, Phys. Rev. Lett. 98, 192501 (2007).
[6] W. Horiuchi and Y. Suzuki, Phys. Rev. C87, 034001 (2013).

# 2014年

11/14
15:00
RIKEN main building, room 433
Hyun-Chul Kim (Inha University)
The charge and spin structure of the nucleon and the pion
In the present talk, we review series of recent works on the charge and spin structure of the nucleon and the pion. We emphasize the new concept of the transverse charge and spin densities of hadrons. The corresponding results are discussed.

09/29
15:00
RIKEN main building, room 124-126
Sho Nagao(永尾翔) (Tohoku University)
Spectroscopy of electro-produced hypernuclei at Mainz Microtron

See here (PDF file).

08/01
13:30

07/18
15:00
RIKEN main building, room 124-126
Toshiyuki Gogami(後神利志) (Kyoto University)
Spectroscopic research of \Lambda hypernuclei with high quality electron beam at Jefferson Lab

See here (PDF file).

04/18
13:00
RIKEN main building, room 124-126

2次元ヘリウム3の基底状態

[1] D. Sato, K. Naruse, T. Matsui, and H. Fukuyama, Phys. Rev. Lett.109, 235306 (2012); D. Sato et al., J. Low Temp. Phys. 158, 201 (2010).

# 2013年

12/17
15:00
RIKEN main building, room 213
Hyun-Chul Kim (Inha University)
Transverse charge and spin structures of the pion and the nucleon

The transverse charge and spin densties provide a novel aspect on the structure of the nucleon, since they reveal internal quark-gluon structures of the nucleon.
We review a series of recent works on the transverse charge and spin densities of the pion and the nucleon, based on the chiral quark-(soliton) model. We first discuss the transverse spin densities of the pion, which can be obtained from the electromagnetic and tensor form factors. We then discuss the transverse charge and spin structures of the nucleon. In particular, we report the first results of the transverse strange charge and spin densities.
Finally, we also show how the transverse charge densities undergo changes in nuclear matter based on the Skyrme model.

12/10
16:00
RIKEN main building, room 213
Yasuhiro Yamaguti (山口康宏) (大阪大学核物理研究センター)
Exotic baryons from a heavy meson and a nucleon

これらは単純なクォーク模型では説明することが難しいエキゾチックな構造を持っているが、なかでもメソン-反メソンの閾値近傍では、そのメソン-反メソンが緩く束縛した「ハドロン分子状態」とよばれる構造を持った粒子の存在が議論されている。

パイオン交換力の中でも特にテンソル力と呼ばれる力が強い引力を生み出す事はすでに原子核物理で知られており、ヘビーメソン系でも同様にハドロン分子状態を形成する原動力となることが期待される。

12/03
15:00
RIKEN main building, room 213
Jiangming Yao (堯江明) (Tohoku University and Southwest University)
Beyond mean‐field description of impurity effect of Lambda hyperon on nuclear collective excitations

See here (PDF file).

11/08
15:00
RIKEN main building, room 213
Y. Taniguchi (University of Tsukuba)
Cluster correlations in deformed states
Structures of deformed states in sd-shell nuclei are discussed focusing on cluster correlations. Recently, rotational bands of largely deformed states have been observed by \gamma-spectroscopy experiments in A \sim 40 region such as 36,40Ar, 40Ca and 44Ti.
Some of the deformed states are strongly populated by cluster-transfer reactions. In order to understand those properties, both of clustering and deformations should be taken into account.
I will briefly introduce basics of clustering and deformations in nuclei, and discuss cluster correlations in largely deformed states of A \sim 30-40 nuclei such as Si, S, and Ca isotopes.

10/21-25
RIKEN main building
List of speakers is here
Workshop: "Multi-particle resonances and astrophysical reaction problems in few-body systems"

The details of this workshop: program and photo

08/28
13:30
RIKEN main building, room 213
Ellena Botta (INFN - Sezione di Torino and Torino University)
Highlights on n-rich $\Lambda$-Hypernuclei from the FINUDA experiment

See here (PDF file).

05/27
14:00
RIKEN main building, room 213
N. Yamanaka (Kyoto University)
Electric dipole moments and supersymmetric CP violation
The electric dipole moment (EDM) is an observable sensitive to the CP violation, with very small standard model prediction, and it is a very good probe of new physics beyond the standard model.
In this talk, we will present the physics of the EDM from the elementary to nuclear level together with our works, by focusing on the supersymmetry as the leading candidate of new physics.
We will also discuss the possibility to constrain the supersymmetric CP phases with prospective experiments.

03/18
14:00
RIKEN main building, room 213
T. Takahashi (Gunma National Cllege of Technology)
Charmed hadron coupling constants from Lattice QCD
We study charmed-hadron coupling constants based on 2+1-flavor lattice QCD.
By computing hadronic form factors, coupling constants between charmed-hadrons and mesons (D*D\pi, DD\rho, DD*\rho) are evaluated.
We discuss the flavor-SU(4) symmetry breaking in coupling constants,
and evaluate electromagnetic radii of light and charm quarks in charmed mesons.
(If possible) We will show our preliminary results of charmed-baryon couplings.

02/05
16:00
RIKEN main building, room 213
Yongseok Oh (Kyungpook National University)
Properties of hyperons with multi strangeness
The operation of J-PARC opens a new window for studying hyperons. In this talk, several interesting problems in hyperon spectrum which can be investigated at J-PARC will be discussed.
We first discuss the strong model-dependence of Xi and Omega hyperon spectrum and the issue on the structure of several hyperon resonances. Then the question on the determination of spin-parity quantum numbers of Xi hyperons will be shortly mentioned.

# 2012年

12/10
16:00
RIKEN main building, room 213
S.X. Nakamura (YITP)
Dynamical coupled-channels model for meson productions and application to strange nuclear physics
Modern experiments require sophisticated analysis tools for
interpreting and extracting interesting physics from their data. For
hadronic and/or nuclear reactions, such analysis tools are often
theoretical models constructed with hadronic degrees of freedom. As
such, I discuss a dynamical coupled-channels model developed for
analyzing meson-baryon reaction data,  thereby extracting baryon
resonances. This dynamical model also has a great potential, with some
extensions, for analyzing J-PARC data, and studying strange nuclear
physics. I will discuss our ongoing effort towards this direction.

11/13
16:00
RIKEN main building, room 213
James S. M. Anderson (Univ. of Tokyo)
GKCI Approach for Solving the Electronic and Nuclear Schroedinger Equation
Achieving high accuracy in both electronic and nuclear structure computations
is a priority when developing a structure method. The full configuration interaction (Full-CI)
method achieves the highest accuracy within a model space, but is very computationally
expensive (exponential scaling).  Full-CI is a robust method that can be used with any Hamiltonian.
It does not take advantage of the inherent smoothness associated with the solutions
to the electronic and nuclear structure Hamiltonians.  In the nuclear structure problem
simplicity arises from every nucleon being identical (in the isospin formalism),
and that the Hamiltonian only contains one- and two-body symmetric operators
(though three-body operators are becoming more prominent).  The same is true in the electronic structure problem.
Our approach takes into account these symmetries that are neglected in the Full-CI approach.
Results from Griebel[1] and others[2-4] in the mathematics of complexity literature show
how one may construct a truncated Full-CI that has polynomial scaling but maintains Full-CI accuracy
(at least within the large model space limit).  We refer to this approach as GK-CI.[5]
A special case of the method is similar to the no-core shell model.  In this presentation
the mechanics of the approach will be explained as well as preliminary results.

References
1. M. Griebel and S. Knapek, Constr. Approx. 16, 525 (2000).
2. H. Bungartz and M. Griebel, Acta Numer. 13, 147 (2001).
3. G.W. Wasilkowski and H. Wozniakowski, Found. Comput. Math., 5, 240 (2005)
4. S.A. Smolyak, Dokl. Akad. Nauk 4, 240 (1963)
5. J.S.M. and P.W. Ayers, J. Chem. Phys., J. Chem. Phys. Submitted (2011).

11/12
14:30
RIKEN main building, room 213
D. Satow (Kyoto. U)
Ultrasoft Fermion Mode in Hot or Dense Boson-Fermion System
Investigation of fermion spectrum in a boson-fermion system
such as QED/QCD at high temperature (T) or chemical potential (μ) is
very important because it
gives us the information on the basic building block of the system.
In contrast to the case that the energy scale is of order gT or gμ (g:
coupling constant), in which the method for perturbative analysis
called "hard thermal/dense loop approximation" has been established,
perturbative analysis in p<< g^2T region is difficult because of the
infrared singularity.

In this seminar, we find a novel fermionic excitation and obtain the
expression of the dispersion relation, the decay width, and the
strength, using the resummed perturbation theory regularizing that
singularity in a hot QED/QCD plasma.
We also find that the excitation disappears in the high density case,
and discuss the reason of the disappearnce.

Finally we derive the new generalized Boltzmann equation which is
equivalent to the resummed perturbation from Kadanoff-Baym equation.
By using that equivalence, we discuss kinetic interpretation of the
resummed perturbation scheme, and show that the terms whose origin is
different from those in the Boltzmann equation, appear in that kinetic
equation.

10/29
16:00
RIKEN main building, room 213
Chiho Nonaka (Nagoya. U)
Dynamical model based on relativistic hydrodynamics for relativistic heavy ion collisions
Since the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National
Laboratory (BNL) started its operation in 2000, a lot of discovery has been made and
a lot of insight related to quantum chromodynamics (QCD) phase transition and the
Quark-Gluon Plasma (QGP) has been gained.
One of the most physically interesting and surprising outcomes at RHIC is the
production of the strongly interacting QGP (sQGP).
Besides, at Large Hadron Collider (LHC) heavy ion collision experiments
started in 2010.
To understand experimental data at RHIC and LHC comprehensively,
construction of realistic dynamical model for description of relativistic hydrodynamic
model is indispensable.

First I outline the modeling of a realistic dynamical model based on
relativistic hydrodynamics for comprehensive description of high energy heavy
ion collisions.
Comparing theoretical calculations and experimental data at RHIC and LHC,
I  will give brief explanation of the key ingredients for the construction of a
multi-module model: initial condition, hydrodynamical expansion,
Then I will discuss our recent development of state-of- the-art relativistic
viscous hydrodynamic model and its application to relativistic heavy ion collisions.

07/23
RIKEN main building 4F conference room 435,437
Dr. Nobutoshi Yasutake [安武 伸俊] (Chiba Inst. Tech.)
Thermodynamical description of hadron-quark phase transition and its implications on compact-star phenomena
One of the most promising possibilities may be the appearance of quark
matter in astrophysical phenomena in the light of recent progress in
observations. The properties of deconfinement is not well understood,
but the thermodynamical aspects of hadron-quark (HQ) phase transition
have been extensively studied in recent years. Then the mixed phase of
hadron and quark matter becomes important; the proper treatment is
needed to describe the HQ phase transition and derive the equation of
state (EOS) for hadron-quark matter, based on the Gibbs conditions for
phase equilibrium. We here use a realistic EOS for hyperonic matter in
the hadron phase. For quark matter we further try to improve the
previous EOS by considering other effective models of QCD. One of the
interesting consequences may be the appearance of the inhomogeneous
structures called ”pasta”, which are brought about by the surface and
the Coulomb interaction effects. We present here a comprehensive review
of our recent works about the HQ phase transition in various
astrophysical situations: cold catalyzed matter, hot matter and neutrino
-trapped matter. We show how the pasta structure becomes unstable by the
charge screening of the Coulomb interaction, thermal effect or the
neutrino trapping effect. Such inhomogeneous structure may affect
astrophysical phenomena through its elasticity or thermal properties.
Here we also discuss some implications on supernova explosion,
gravitational wave and cooling of compact stars.

07/09
16:00
RIKEN main building, room 213
Mr. Zhou Bo [周 波] (RCNP)
New concept for the ground-state band in 20Ne within a microscopic cluster model
function was proposed,  which has been quite successful in describing the
dilute gas-like states in light nuclei  and indeed leads us to have a new
perspective for the n alpha cluster structure in light 4n nuclei.  Now,  we
propose a generalized wave function based on the flexible original THSR
wave function , which is applicable to studies of general cluster
structures in nuclei. The ground-state band in 20Ne is investigated  by
using this generalized wave function and the energies obtained agree well
with the experimental values. Moreover, it is found that the single
generalized THSR wave functions almost completely coincide  with the exact
solutions of  alpha+16O resonating group method for the ground-state band
in 20Ne. For the ground state, for instance, the squared overlap between
them is 99.3%.  Therefore  we have a new concept for understanding the
compact structure of the ground-state band in 20Ne, which provides a more
exact picture than the Brink cluster model.  On the other hand,  we can
conclude  that the THSR model wave function can also be extended to study
more compact cluster states in nuclei such as, e.g., the ground-state band
in 20Ne.

06/29
16:00
RIKEN main building, room 213

Coulomb Breakup and Reaction Cross Sections for Deformed Halo Nucleus 31Ne
A halo structure with an extended density distribution is one of the characteristic
features of weakly bound neutron-rich nuclei. For the neutron-rich nucleus 31Ne,
the halo structure has been recently suggested by the experimental data of Coulomb breakup
and interaction cross sections measured at RIKEN RIBF facility.
Assuming that 31Ne consists of the strongly deformed core nucleus 30Ne and one valence neutron,
we calculate Coulomb breakup and reaction cross sections of 31Ne taking into account
the rotational excitation energy of the core nucleus 30Ne with particle-rotor model (PRM).
We will discuss the structure of 31Ne deduced from these calculations.

05/28
16:00
RIKEN main building, room 213

Structure study of p-sd shell and neutron-rich $\Lambda$ hypernuclei by using AMD
In this talk, we will discuss the structure of several p-sd shell and
neutron-rich $\Lambda$ hypernuclei such as Be, Ne and Mg, based
on the antisymmetrized molecular dynamics (AMD) calculation.
Forthcoming experiments at J-PARC will reveal the spectroscopy
of sd-shell and neutron-rich $\Lambda$ hypernuclei. One of the
unique and interesting aspects of hypernuclei is the structure
change caused by hyperon. Through the interaction with surrounding
nucleons, a hyperon in the atomic nucleus can affect and modify
nuclear clustering and deformation. Especially, the structure
changes of sd-shell and neutron-rich $\Lambda$ hypernuclei are
of interest, since the various clustering and deformed structures
coexist in the ground and low-lying excited states.

To study such phenomena, we have extended the AMD for hypernuclei
and applied it. By using the YNG and Gogny D1S as effective $\Lambda$N
and NN interactions, we investigated the low-lying structure of Be, Ne and
Mg $\Lambda$ hypernuclei without any assumption on the clustering and
deformation. In this talk, we will show you the excitation spectra of such
$\Lambda$ hypernuclei and discuss the structure changes caused
by $\Lambda$ hyperon.

05/23
16:00
RIBF Building, 2F large meeting room
【肥山研・中務研共催セミナー】 民井 淳(RCNP)
Tensor Correlation in the Ground States of N=Z Nuclei
The nucleon-nucleon (NN) interaction contains a strong tensor interaction due to pion exchange. The strong attraction of the tensor interaction contributes significantly to the binding energy of nuclei. Therefore it is natural to treat the tensor interaction explicitly in nuclear structure calculations. Such calculations are, however, limited in few-nucleon systems due to mainly technical difficulty. Thus the role of the tensor interaction, or tensor correlation, in nuclear structure has not been explicitly taken into account in conventional shell-model and mean-field calculations, and has been hidden.
Experimental trial for probing the effects of tensor correlation is one of hot topics. We have recently observed bulk contribution of the tensor correlation in the ground states of self-conjugate (N=Z) even-even nuclei. The experiment was performed at the Research Center for Nuclear Physics (RCNP), employing a high-resolution proton beam at 295 MeV and the Grand Raiden spectromter. Spin-M1 transition strengths from the ground states of 12C, 16O, 20Ne, 24Mg, 28Si, 32S, 36Ar, and 40Ca nuclei have been determined for each of isoscalar and isovector transitions up to 16 MeV. The observed transition strengths are converted, by using a sum-rule, to an expected value of the ground state wave-function ＜S_p . S_n＞, where S_p(n) is the vector-sum of all the proton (neutron) spin-operators. The value is quite sensitive to the tensor correlation between protons and neutrons. The extracted number is ~0.1 and is more or less flat in sd-shell region. The number is consistent with predictions for the 4He nucleus using realistic NN interactions.
I will report on the experiment and discuss the results.

05/14
14:30
RIKEN main building, room 213

Charm quark physics from lattice QCD
We investigate the charm quark system using the relativistic heavy quark action on 2+1 flavor PACS-CS configurations.
The dynamical up-down and strange quark masses are set to the physical values by using the technique of reweighting to shift the quark hopping parameters from the values employed in the configuration generation. The charm quark mass is determined by the spin-averaged mass of the 1S charmonium state. We also calculated the Cabibbo-Kobayashi-Maskawa matrix elements, |V_{cd}| and |V_{cs}|, extracted from the charmed and charmed-strange meson decay constants.

05/07
16:00
RIKEN main building, room 213

Baryon number probability distribution in the presence of second order phase transition
We discuss the probability distribution of a net conserved charge based on the Landau theory of phase transition. Statistical fluctuations of the net baryon number, especially of higher orders, have been regarded as diagnostics of the chiral phase transition in QCD. Normally they are discussed by calculating cumulants of the net baryon number through derivatives of the thermodynamic pressure with respect to the chemical potential in the grand canonical ensemble. Lattice QCD and effective model calculations have revealed their critical behaviors in the vicinity of the chiral phase transition. The purpose of this work is to characterize the critical behavior in terms of the probability distribution.

We construct an analytically solvable model which respects relevant symmetries based on the Landau theory within mean field approximation. We clarify differences in the probability distribution originated from the singular part of the thermodynamic potential. Then, we consider an extension by implementing O(4) critical scaling in the model pressure such that higher order cumulants (c3 and c4) diverge at the phase transition. We emphasize the relationship of the probability distribution to the analytic structure of the grand canonical partition function in complex chemical potential. It is pointed out that the singular structure, which gives the divergent cumulants, leads to an anomalous oscillatory factor in the probability distribution through both numerical calculations and analytic consideration.

04/23
16:00
RIKEN main building, room 213
Lie Ang
Massive neutron stars and the equation of state of matter at high densities
We perform Brueckner-Hartree-Fock calculations of kaon-condensed matter, hypernuclear matter and hybird matter,
and compute the structure of neutron stars within this approach.
We conclude that kaon condensation may be totally suppressed in our model,
but low maximum masses below 2 solar masses are found for hyperon stars and hybrid stars.

04/17
11:30
RIKEN main building, room 213

Lee-Yangの量子クラスター展開法を用いた非対角長距離秩序の判定条件
ユニタリー・フェルミ気体の熱力学関数が、３つのグループにより実験的に計測された[1]。これらの実験結果を解析する理論的なアプローチの一つとして、フガシティz=exp(βμ)による展開（クラスター展開）が注目されている。多くの先行研究により、3次や4次の低次の係数が数値的に求められた[2]。しかし、相転移を扱うには、高次の項を取り入れる必要がある。我々は、クラスター展開の高次の項を系統的に扱うために、Lee-Yangの量子クラスター展開法[3]を拡張した[4]。拡張された方法を用いれば、ボース系やフェルミ系の大分配関数とN

6]についても簡単に触れる予定である。

[1] M. Horikoshi et al., Science 327, 442 (2010); S. Nascimbne et
al., Nature 463, 1057 (2010); M. J. H. Ku et al., Science, 335, 563
(2012).
[2] G. Rupak, PRL 98, 090403 (2007); X.-J. Liu et al., PRL 102, 160401
(2009); D. B. Kaplan and S. Sun, PRL 107, 030601 (2011).
[3] T. D. Lee and C. N. Yang, Phys. Rev. 113, 1165 (1958); 117, 22 (1960).
[4] N. Sakumichi, N. Kawakami and M. Ueda, Phys. Rev. A 85, 043601 (2012).
[5] N. Sakumichi, N. Kawakami and M. Ueda, arXiv:1202.6532 (2012).
[6] N. Sakumichi, Y. Nishida and M. Ueda, in preparation.

04/16
14:00
RIKEN main building, room 213
Koike Takahisa
Formation of light Xi^- hypernuclei via (K^-, K^+) reaction
The Xi-N interaction is not well-known, other than it could be weakly
attractive. An experimental search of Xi^- hypernucleus via (K^-, K^+)
reaction on 12C target is planned at J-PARC as E05.
Many authors have theoretically performed the calculation of (K^-, K^+)
reaction spectra on 12C and the heavier targets with the closed shell,
while none for the lighter target than 12C so far. On the other hand,
Hiyama et al. have predicted the existence of Xi^- hypernuclear bound
state for several light $p$-shell nuclei by the few-body structure
calculation. Thus, our purpose is to calculate the (K^-, K^+) reaction
spectra on light p-shell targets and examine their experimental feasibility.

In this talk, we focus on the 7Li target case, which forms
[Xi^- + 6He] bound state via (K^-, K^+) reaction.
The expected reaction spectrum is calculated within the framework
of distorted wave impulse approximation (DWIA) using coupled-channel
Green's function method considering [Xi^- + 6He(0+)]-[Xi^- + 6He(2+)]
channel coupling.

04/09
13:00
RIKEN main building, room 213
Suno Hiroya [PPT]
A diabatic hyperspherical study of traiatomic helium systems
Luncheon Seminar
03/05
15:00-
RIKEN main building, room 213
Shigehiro Nagataki (YITP)
General Relativistic Magneto-Hydrodynamic Simulations of Gamma-Ray Bursts
Gamma-Ray Bursts (GRBs) are the most powerful explosions in the Universe. Recently, it is found that some GRBs are born with peculiar supernova explosions. The explosion energy of the peculiar supernovae is about 10 times greater than that of normal supernovae. That is why it is believed that the central engine of GRBs is different from the one of normal supernovae. However, it is not known well how the engine of GRBs is working. In this talk, I would like to review the history of the study on the central engine of GRBs and I would like to present my recent numerical simulations (General Relativistic Magneto-Hydrodynamic Simulations) of the engine. Also, I would like to show briefly some our recent works that are related with GRB phenomena.

# 2011年

12/2
Evening
RIKEN
The 6th Interdisciplinary Exchange Evening
12/22
15:00-
RIKEN main building, room 213
Hideko Nagahiro (Nara Women's University) [PPT]
Composite and elementary natures of hadrons
-- Study of mixing properties of a1(1260) --
One of recent interests in the hadron structure is whether hadrons are made up of quarks and gluons confined in a single-particle potential as described in the conventional quark model, or rather develop subcomponents of quark-clusters inside hadrons.  It has been suggested that some hadronic resonances could have substantially large components of hadronic composites.  In view of the fact that hadronic resonant states are unavoidably mixture of hadronic and quark-composites, an important issue is to clarify how these components are mixed in a hadron.

In this talk, we focus on hadron structure having two components of hadronic composite and elementary component, by taking the a1(1260) meson as an example.  The problem is analyzed in a manner similar to a two-level problem with mixing in quantum mechanics. We propose a method to disentangle their mixture appearing in the physically observed state.