arXiv subjects

Emiko Hiyama

Publications and source records attributed to Emiko Hiyama.

At least 55 records · Page 3Linked to original sources

arXiv2017

Electric dipole moment of $^{13}$C

We calculate for the first time the electric dipole moment (EDM) of $^{13}$C generated by the isovector CP-odd pion exchange nuclear force in the $α$-cluster model, which describes well the structures of low lying states of the $^{13}$C nucleus. The linear dependence of the EDM of $^{13}$C on the neutron EDM and the isovector CP-odd nuclear coupling is found to be $d_{^{13}{\rm C}} = -0.33 d_n - 0.0020 \bar G_π^{(1)}$. The linear enhancement factor of the CP-odd nuclear coupling is smaller than that of the deuteron, due to the difference of the structure between the $1/2^-_1$ state and the opposite parity ($1/2^+$) states. We clarify the role of the structure played in the enhancement of the EDM. This result provides good guiding principles to search for other nuclei with large enhancement factor. We also mention the role of the EDM of $^{13}$C in determining the new physics beyond the standard model.

nucl-th↗

arXiv2017

Modelling double charge exchange response function for tetraneutron system

This work is an attempt to model the $4n$ response function of a recent RIKEN experimental study of the double charge exchange $^4$He($^8$He,$^8$Be)$^4$n reaction in order to put in evidence an eventual enhancement mechanism of the zero energy cross section, including a near-threshold resonance. This resonance can indeed be reproduced only by adding to the standard nuclear Hamiltonian an unphysically large T=3/2 attractive 3n-force which destroys the neighboring nuclear chart. No other mechanisms like cusps or related structures were found.

nucl-th↗

arXiv2017

Instanton effects on the heavy-quark static potential

We investigate the instanton effects on the heavy-quark potential,including its spin-dependent part, based on the instanton liquid model. Starting with the central potential derived from the instanton vacuum, we obtain the spin-dependent part of the heavy-quark potential. We discuss the results of the heavy-quark potential from the instanton vacuum. We finally solve the nonrelativistic two-body problem, associating with the heavy-quark potential from the instanton vacuum. The instanton effects on the quarkonia spectra are marginal but are required for quantitative description of the spectra.

hep-ph↗

arXiv2017

Search for Tetraneutron by Pion Double Charge Exchange Reaction at J-PARC

Tetraneutron ($^4n$) has come back in the limelight, because of recent observation of a candidate resonant state at RIBF. We propose to investigate the pion double charge exchange (DCX) reaction, i.e. $^4\mathrm{He}(π^- , π^+)$, as an alternative way to populate tetraneutron. An intense $π^-$ beam with the kinetic energy of ~850 MeV, much higher than that in past experiments at LAMPF and TRIUMF, will open up a possibility to improve the experimental sensitivity of the formation cross section, which will be much smaller than hitherto known DCX cross sections such as $^9\mathrm{Be}(π^-, π^+)^9\mathrm{He}\ (g.s.)$.

nucl-ex↗

arXiv2016

Trimer and Tetramer Bound States in Heteronuclear Systems

The Efimov effect in heteronuclear cold atomic systems is experimentally more easily accessible than the Efimov effect for identical atoms, because of the potentially smaller scaling factor. We focus on the case of two or three heavy identical bosons and another atom. The former case was recently observed in a mixture of 133Cs and 6Li atoms. We employ the Gaussian Expansion Method as developed by Hiyama, Kino et al.. This is a variational method that uses Gaussians that are distributed geometrically over a chosen range. Supplemental calculations are performed using the Skorniakov-Ter-Martirosian equation. Blume et al. previously investigated the scaling properties of heteronuclear systems in the unitary limit and at the three-body breakup threshold. We have completed this picture by calculating the behaviour on the positive scattering length side of the Efimov plot, focussing on the dimer threshold.

cond-mat.quant-gas↗

arXiv2016

Nuclear electric dipole moment of light nuclei in the gaussian expansion method

The nuclear electric dipole moment is a very sensitive probe of CP violation beyond the standard model, and for light nuclei, it can be evaluated accurately using few-body calculational methods. In this talk, we present the deuteron, $^3$He, $^3$H, $^6$Li, and $^9$Be electric dipole moments calculated using the Gaussian expansion method with a realistic nuclear force, and assuming the one-meson exchange model for the P, CP-odd nuclear force. We then give future prospects for models beyond the standard model such as the supersymmetry.

nucl-th↗

arXiv2016

Standard model contribution to the electric dipole moment of the deuteron, $^3$H, and $^3$He nuclei

We calculate for the first time the electric dipole moment (EDM) of the deuteron, $^3$H, and $^3$He nuclei generated by the one-meson exchange CP-odd nuclear force in the standard model. The effective $|ΔS| = 1$ four-quark operators are matched to the $|ΔS| = 1$ standard model processes involving the CP phase of the Cabibbo-Kobayashi-Maskawa matrix at the electroweak scale and run down to the hadronic scale $μ= 1$ GeV according to the renormalization group evolution in the next-to-leading logarithmic order. At the hadronic scale, the hadron matrix elements are modeled in the factorization approach. We then obtain the one-meson (pion, eta meson, and kaon) exchange CP-odd nuclear force, which is the combination of the $|ΔS| = 1$ meson-baryon vertices which issue from the penguin operator and the hyperon-nucleon transition. From this CP-odd nuclear force, the nuclear EDM is calculated with the realistic Argonne $v18$ interaction and the CP-odd nuclear force using the Gaussian expansion method. It is found that the EDMs of light nuclear systems are of order $O(10^{-31}) e $ cm. We also estimate the standard model contribution to other hadronic CP violating observables such as the EDMs of $^6$Li, $^9$Be nuclei, and the atomic EDMs of $^{129}$Xe, $^{199}$Hg, $^{211}$Rn, and $^{225}$Ra generated through the nuclear Schiff moment. We then analyze the source of theoretical uncertainties and show some possible ways to overcome them.

hep-ph↗

arXiv2016

Charmed baryons and their interactions

In this proceedings report, we discuss unique features of charmed, or in general heavy, baryons with one heavy quark. A well and long-term known phenomena, the distinction of the two modes of the rho and lambda type of a three-quark system is revisited. The difference of these modes may be tested in the production and decay reactions of the baryons which may be tested in the future experiments at J-PARC.

hep-ph↗

arXiv2016

A model of charmed baryon-nucleon potential and 2- and 3-body bound states with charmed baryon

A potential model for the interaction between a charmed baryon ($Λ_c$, $Σ_c$, and $Σ_c^*$) and the nucleon ($N$) is constructed. The model contains a long-range meson ($π$ and $σ$) exchange part and a short-distance quark exchange part. The quark cluster model is used to evaluate the short-range repulsion and a monopole type form factor is introduced to the long-range potential to reflect the extended structure of hadrons. We determine the cutoff parameters in the form factors by fitting the $NN$ scattering data with the same approach and we obtain four sets of parameters (a -- d). The most attractive potential (d) leads to bound $Λ_c N$ states with $J^π= 0^+$ and $1^+$ once the channel couplings among $Λ_c$, $Σ_c$ and $Σ_c^*$ are taken into account. One can also investigate many-body problems with the model. Here, we construct an effective $Λ_c N$ one-channel potential with the parameter set (d) and apply it to the 3-body $Λ_c NN$ system. The bound states with $J=1/2$ and $3/2$ are predicted.

nucl-th↗

arXiv2015

Spectrum of heavy baryons in the quark model

Single- and double- heavy baryons are studied in the constituent quark model. The model Hamiltonian is chosen as a standard one with two exceptions : (1) The color-Coulomb term depend on quark masses, and (2) an antisymmetric $LS$ force is introduced. Model parameters are fixed by the strange baryon spectra, $Λ$ and $Σ$ baryons. The masses of the observed charmed and bottomed baryons are, then, fairly well reproduced. Our focus is on the low-lying negative-parity states, in which the heavy baryons show specific excitation modes reflecting the mass differences of heavy and light quarks. By changing quark masses from the SU(3) limit to the strange quark mass, further to the charm and bottom quark masses, we demonstrate that the spectra change from the SU(3) symmetry patterns to the heavy quark symmetry ones.

hep-ph↗

arXiv2015

Enhancement of the CP-odd effect in the nuclear electric dipole moment of $^6$Li

We calculate for the first time the electric dipole moment (EDM) of the $^6$Li nucleus within the alpha + p + n three-body cluster model using the Gaussian expansion method, assuming the one meson exchange P, CP-odd nuclear forces. It is found that the EDM of the $^6$Li is 2 times more sensitive on the isovector pion exchange P, CP-odd nuclear force than the deuteron EDM, due to the CP-odd interaction between the nucleons and the alpha cluster. The $^9$Be EDM is also calculated in the same framework as an alpha + alpha + n three-body system. We also test the ab initio calculation of the EDM of the deuteron, $^3$H and $^3$He nuclei using the realistic Argonne $v18$ nuclear force. In the ab initio calculations, good agreements with previous studies are obtained. We finally discuss the prospects for the new physics beyond the standard model.

nucl-th↗

arXiv2014

$K^-d\rightarrow πΣn$ reactions and structure of the $Λ(1405)$

We report on the first results of a full three-body calculation of the $\bar{K}NN$-$πYN$ amplitude for the $K^-d\rightarrowπΣn$ reaction, and examine how the $Λ(1405)$ resonance manifests itself in the neutron energy distributions of $K^-d\rightarrowπΣn$ reactions. The amplitudes are computed using the $\bar{K}NN$-$πYN$ coupled-channels Alt-Grassberger-Sandhas (AGS) equations. Two types of models are considered for the two-body meson-baryon interactions: an energy-independent interaction and an energy-dependent one, both derived from the leading order chiral SU(3) Lagrangian. These two models have different off-shell properties that cause correspondingly different behaviors in the three-body system. As a remarkable result of this investigation, it is found that the neutron energy spectrum, reflecting the $Λ(1405)$ mass distribution and width, depends quite sensitively on the (energy-dependent or energy-independent) model used. Hence accurate measurements of the $πΣ$ mass distribution have the potential to discriminate between possible mechanisms at work in the formation of the $Λ(1405)$.

nucl-th↗

arXiv2014

Superdeformed $Λ$ hypernuclei from relativistic mean field models

We study the superdeformed (SD) states and corresponding SD hypernuclei of Ar isotopes with the multidimensionally-constrained relativistic mean field (MDC-RMF) models which can accommodate various shape degree of freedom. %The hyperon-nucleon $σ$-$Λ$ and $ω$-$Λ$ interactions are introduced %in the same covariant framework. We found that the density profiles of SD states in Ar isotopes show a strong localization with a ring structure near the surface, while the central part of the density is dilute showing a hole structure. This localization of SD density induces an appreciable deformation in the hyperon wave function and results in a large overlap between the core and the hyperon in the SD hypernuclei of Ar isotopes. Then the $Λ$ separation energy of SD state becomes larger than that of normally deformed or spherical ground state. This feature is different from that found in other nuclei such as $^{32}$S, $^{56}$Ni, and $^{60}$Zn in which the $Λ$ separation energy of larger deformed state is smaller. In this context, the measurement of the $Λ$ separation energy may provide an important information on the localization of the density profile of SD states.

nucl-th↗

arXiv2014

Superdeformed $Λ$ hypernuclei with antisymmetrized molecular dynamics

The response to the addition of a $Λ$ hyperon is investigated for the deformed states such as superdeformation in $^{41}_Λ$Ca, $^{46}_Λ$Sc and $^{48}_Λ$Sc. In the present study, we use the antisymmetrized molecular dynamics (AMD) model. It is pointed out that many kinds of deformed bands appear in $^{45}$Sc and $^{47}$Sc. Especially, it is found that there exists superdeformed states in $^{45}$Sc. By the addition of a $Λ$ particle to $^{40}$Ca, $^{45}$Sc and $^{47}$Sc, it is predicted, for the first time, that the superdeformed states exist in the hypernuclei $^{41}_Λ$Ca and $^{46}_Λ$Sc. The manifestation of the dependence of the $Λ$-separation energy on nuclear deformation such as spherical, normal deformation and superdeformation is shown in the energy spectra of $^{41}_Λ$Ca, $^{46}_Λ$Sc and $^{48}_Λ$Sc hypernuclei.

nucl-th↗

arXiv2014

Alpha-clustered hypernuclei and chiral SU(3) dynamics

Light hypernuclei with an $α$ cluster substructure of the core nucleus are studied using an accurate cluster approach (the Hyper-THSR wave function) in combination with a density-dependent $Λ$ hyperon-nuclear interaction derived from chiral SU(3) effective field theory. This interaction includes important two-pion exchange processes involving $ΣN$ intermediate states and associated three-body mechanisms as well as effective mass and surface terms arising in a derivative expansion of the in-medium $Λ$ self-energy. Applications and calculated results are presented and discussed for $_Λ^9$Be and $^{13}_Λ$C. Furthermore, the result of the lightest $α$ clustered hypernucleus, $^5_Λ$He using realistic $ab initio$ four nucleon density is shown.

nucl-th↗

arXiv2013

Possible Existence of Charmonium-Nucleus Bound States

Possible existence of $(c\bar{c})-$nucleus bound states are examined. We adopt Gaussian potentials for the $η_{c}-N$ and $J/ψ-N$ interactions. The relations between the scattering lengths $a$ of $(c\bar{c})-N$ interactions and the binding energies of $η_{c}-NN$, $J/ψ-NN$ and $J/ψ-^{4}$He are given. The results show that scattering lengths $a \le -0.95$ fm are needed to make $η_{c}-NN$ and $J/ψ-NN$ bound states, while for $a \le -0.24$ fm there may exist a $J/ψ-^{4}$He bound state.

nucl-th↗

arXiv2013

Complex-Scaling Calculation of Three-Body Resonances Using Complex-Range Gaussian Basis Functions --- Application to 3$α$ resonances in 12C ---

We propose to use the complex-range Gaussian basis functions, {r^l e^{-(1 \pm iω)(r/r_n)^2}Y_{lm}(\hat{r}); r_n in a geometric progression}, in the calculation of three-body resonances with the complex-scaling method (CSM) in which use is often made of the real-range Gaussian basis functions, {r^l e^{-(r/r_n)^2}Y_{lm}(\hat{r})}, that are suitable for describing the short-distance structure and the asymptotic decaying behavior of few-body systems. The former basis set is more powerful than the latter when describing the resonant and nonresonant continuum states with highly oscillating amplitude at large scaling angles θ. We applied the new basis functions to the CSM calculation of the 3αresonances with J=0^+, 2^+ and 4^+ in 12C. The eigenvalue distribution of the complex scaled Hamiltonian becomes more precise and the maximum scaling angle becomes drastically larger (θ_{max}=16 deg. \arrow 36 deg.) than those given by the use of the real-range Gaussians. Owing to these advantages, we were able to confirm the prediction by Kurokawa and Kato [Phys. Rev. C 71, 021301 (2005)] on the appearance of the new broad 0^+_3 state; we show it as an explicit resonance pole isolated from the 3$α$ continuum.

nucl-th↗

arXiv2012

Structure of $^{10}_Λ$Be and $^{10}_Λ$B hypernuclei studied with the four-body cluster model

The structure of the isodoublet hypernuclei, $^{10}_Λ$B and $^{10}_Λ$Be within the framework of an $α+α+Λ+N$ four-body cluster model is studied. Interactions between the constituent subunits are determined so as to reproduce reasonably well the observed low-energy properties of the $αα$, $αN$, $αΛ$, $ααΛ$ and $ααN$ subsystems. Furthermore, the two-body $ΛN$ interaction is adjusted so as to reproduce the $0^+$-$1^+$ splitting of $^4_Λ$H. The $Λ$ binding energies of $^{10}_Λ$B and $^{10}_Λ$Be are 8.76 MeV and 8.94 MeV, respectively. The energy splitting of the $1^-$-$2^-$ levels in $^{10}_Λ$B is 0.08 MeV, which does not contradict the experimental report in BNL-E930. An even-state $ΛN$ charge symmetry breaking (CSB) interaction determined from the A=4 systems works repulsively by +0.1 MeV (attractively by -0.1 MeV) in $^{10}_Λ$Be ($^{10}_Λ$B). We discuss a possibility that an odd-state CSB interaction improves the fitting to the experimental data of A=10 double $Λ$ hypernuclei.

nucl-th↗