Modern Physics Letters A

In this talk I summarize recent findings made on the description of axial vector mesons as dynamically generated states from the interaction of pseudoscalar mesons and vector mesons, dedicating some attention to the two K₁(1270) states. Then I review the generation of open and hidden charm scalar and axial states. Finally, I present recent results showing that the low lying 1/2⁺ baryon resonances for S=−1 can be obtained as bound states or resonances of two mesons and one baryon in coupled channels dynamics.

The chiral structure of heavy-light mesons is explored with a particular focus on the nature of the D_sJ charmed mesons. Theoretical predictions for the hadronic and radiative decays of these mesons are compared to recent experimental data.

Current theoretical studies on the σ and κ resonances are reviewed. It is emphasized that all evidences accumulated so far are consistent with the picture that the σ meson is the chiral partner of the Nambu–Goldstone bosons in a linear realization of chiral symmetry.

We discuss internal structure of an exotic hadron by using fragmentation functions. The fragmentation functions for the f₀(980) meson are obtained by a global analysis of e⁺ + e⁻ → f₀ + X data. Quark configuration of the f₀(980) could be determined by peak positions and second moments of the obtained fragmentation functions.

The light scalar nonets are studied using the QCD sum rules for the tetraquark operators. The operator product expansion for the correlators is calculated up to dimension 12 and this enables us to perform analyses retaining sufficient pole-dominance. To classify the light scalar nonets, we investigate the dependence on current quark mass and flavor dynamics. Especially, to examine the latter, we study separately SU(3) singlet and octet states, and show that the number of annihilation diagrams is largely responsible for their differences, which is also the case even after the inclusion of the finite quark mass. Our results support the tetraquark picture for isosinglets, while that for octets is not conclusive yet.

We study the light scalar mesons in the QCD sum rule. We construct both the diquark-antidiquark currents and the meson-meson currents . We find that there are five independent currents for both cases, and derive the relations between them. For the meson-meson currents, five independent currents are formed by products of color singlet pairs or color octet pairs. However, they can be related to each other, and the relations are derived. We obtain the masses of the light scalar mesons which are consistent with the experiments.

We present in this talk recent results of the vector and axial-vector transitions of the nucleon to the pentaquark baryon Θ⁺, based on the SU(3) chiral quark-soliton model. The results are summarized as follows: K^*NΘ vector and tensor coupling constants turn out to be g_K*NΘ ≃ 0.81 and f_K*NΘ ≃ 0.84, respectively, and the KNΘ axial-vector coupling constant to be . As a result, the total decay width for Θ⁺ → NK becomes very small: Γ_Θ→NK ≃ 0.71 MeV, which is consistent with the DIANA result Γ_Θ→NK = 0.36 ± 0.11 MeV.

The recently discovered scalar and axial vector charmed strange mesons are predicted in the hadrogenesis picture. They are generated by coupled-channel dynamics involving the scattering of Nambu-Goldstone bosons off pseudoscalar and vector D(D_s)-meson ground-states. The interaction vertices are given by the leading order chiral Lagrangian and chiral corrections to order . To assess this dynamical picture further, the radiative and strong decays into the isospin-violating π⁰D_s and channels are calculated. A consistent picture of these decays emerges when the parameters are chosen in accordance with expectations from the heavy-quark symmetry and large N_c limit of QCD and when light vector mesons are introduced explicitly in the radiative decay processes. More accurate data are needed to predict decay parameters reliably.

We have performed a theoretical study of the axial Nucleon to Delta(1232) (N → Δ) transition form factors up to one-loop order in covariant baryon chiral perturbation theory within a formalism in which the unphysical spin-1/2 components of the Δ fields are decoupled.

The in-medium properties of charm mesons (D and ) in a hot and dense matter are studied. A self-consistent coupled-channel approach is driven by a broken SU(4)s-wave Tomozawa-Weinberg interaction supplemented by an attractive isoscalar-scalar term. As medium effects, we include Pauli blocking, baryon mean-field bindings, and π and open-charm meson self-energies. The dynamically generated and resonances in the DN sector remain close to their free space position but acquire large widths. The resultant D meson spectral function, which shows a single pronounced quasiparticle peak close to the free mass that broadens with increasing density, also has a long low energy tail associated with smeared , configurations. The low-density approximation for the is questionable already at subsaturation densities. We touch upon the implication of our study for J/Ψ suppression at FAIR.

We propose the enhancement of Λ_c yield in heavy ion collisions at RHIC and LHC as a novel signal for the existence of diquarks in the strongly coupled quark-gluon plasma produced in these collisions as well as in the Λ_c. Assuming that stable bound diquarks can exist in the quark-gluon plasma, we argue that the yield of Λ_c would be increased by two-body collisions between [ud] diquarks and c quarks, in addition to normal three-body collisions among u, d and c quarks. A quantitative study of this effect based on the coalescence model shows that including the contribution of diquarks to Λ_c production indeed leads to a substantial enhancement of the Λ_c/D ratio in heavy ion collisions.

The study presented in this paper shows that accounting for the relativistic structure of the deuteron allows to explain the ratio of the Drell-Yan pair production cross-sections at the low Bjorken x off the deuteron and the proton. Thus, the sea quark distributions in the nucleon should be studied with accounting for the effects of the relativistic structure of the deuteron. The suggested approach reduces theoretical uncertainty in extracting the ratio from the data and it is important for the clarification of the nature of the sea quark asymmetry in the nucleon.

After a brief introduction to the phenomenological nucleon-nucleon (NN) potentials, the basic formulation of deriving the NN potential from lattice QCD simulations on the basis of the equal-time Bethe-Salpeter wave function is presented. The resultant non-local NN potential and its derivative expansion are discussed. Ongoing and planned studies on the lattice with quenched and full QCD simulations are summarized.

Chiral expansions of the two-pion exchange components of both two- and three-nucleon forces are reviewed and a discussion is made of the predicted pattern of hierarchies. The strength of the scalar-isoscalar central potential is found to be too large and to defy expectations from the symmetry. The causes of this effect can be understood by studying the nucleon scalar form factor.

Quenched lattice QCD results of nuclear forces are presented. Inter-nucleon potentials are constructed from Bethe-Salpeter wave functions of two nucleon states by using a Schrödinger-type equation. The results of the central force in ¹S₀ channel posses the repulsive core at short distance as well as the attraction at medium distance, both of which are enhanced in the light quark mass region. A preliminary result on the tensor force is also presented with the central force in ³S₁ channel.

We calculate pΞ⁰ potentials from the equal-time Bethe-Salpeter amplitude measured in the quenched QCD simulation with the spatial lattice volume, (4.4 fm)³. The standard Wilson gauge action with the gauge coupling β = 5.7 on 32⁴ lattice together with the standard Wilson quark action is used. The hopping parameter κ_ud = 0.1678 is chosen for u and d quarks, which corresponds to m_π ≃ 0.37 GeV. The physical strange quark mass is used by taking the parameter κ_s = 0.1643 which is deduced from the physical K meson mass. The lattice spacing a = 0.1420 fm is determined by the physical ρ meson mass. We find that the pΞ⁰ potential has sizable spin dependence. Strong repulsive core is found in ¹S₀ channel while the effective central potential in the ³S₁ channel has relatively weak repulsive core. The potentials also have weak attractive parts in the medium to long distance region (0.6 fm ≲ r ≲ 1.2 fm) in both of the ¹S₀ and ³S₁ channels.

We address the issue of a consistent power counting scheme in manifestly Lorentz-invariant baryon chiral perturbation theory. We discuss the inclusion of vector mesons in the calculation of the nucleon electromagnetic form factors. We comment on the chiral expansion of the nucleon mass to order .

We consider the parity-violating two-pion-exchange potential obtained from the covari-ant formalism in the past and the state-of-the-art effective field theory approach. We discuss the behavior of the potential in coordinate space and its application to the parity-violating asymmetry in at threshold.

Consistent SU(6) and SU(8) spin-flavor extensions of the SU(3) flavor Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian are constructed, which incorporate vector meson degrees of freedom. In the charmless sector, the on-shell approximation to the Bethe-Salpeter (BS) approach successfully reproduces previous SU(3) WT results for the lowest-lying s–wave negative parity baryon resonances. It also provides some information on the dynamics of heavier ones and of the lightest d-wave negative parity resonances, as e.g. the Λ(1520). For charmed baryons the scheme is consistent with heavy quark symmetry, and our preliminary results in the strangeness-less charm C = +1 sector describe the main features of the three-star J^P = 1/2⁻ Λ_c(2595) and J^P = 3/2⁻ Λ_c(2625) resonances. We also find a second broad J^P = 1/2⁻ state close to the Λ_c(2595).

We show that the differential cross section dσ/dt of γp → φp reaction at the threshold has a finite value and it is crucial to the mechanism of the φ meson photoproduction and for the models of φN interaction.

A coupled channels analysis is presented for photo-induced kaon production which is based on the K-matrix approach. Channel coupling effects are large and should not be ignored. It is shown that multiple solutions exist in a model independent analysis. An outlook is given to the possibilities to include constraints due to causality.

We study the threshold production of two pions induced by neutrinos in nucleon targets. The contribution of nucleon pole, pion and contact terms is calculated using a chiral Lagrangian. The contribution of the Roper resonance, neglected in earlier studies, has also been taken into account.

The total cross sections for the π⁺π⁻ photoproduction on the deuteron were measured in an energy range of 0.8 to 1.1 GeV. The obtained total cross section for the quasi-free π⁺π⁻ photoproduction on the deuteron was about 60 % of those on the free proton. The cross section for Δ⁺⁺Δ⁻ photoproduction was derived from the non-quasi-free π⁺π⁻ photoproduction events. It was smaller than the previous data.

We study neutrino-induced one-pion production off the nucleon in and around the Delta resonance region. Apart from the Delta-pole mechanism we include background terms required by chiral symmetry. These background terms give sizeable contributions in all channels. To better reproduce the ANL q²-differential cross section data, we make a new fit of the axial nucleon to Delta form factor. The new result is some 30% smaller than the commonly accepted value. This correction is compatible with most quark model estimates and a recent lattice calculation.¹

We discuss the relevance of nuclear medium effects in the analysis of some low and medium energy neutrino reactions of current interest. In particular, we study the Quasi-Elastic (QE) process, where RPA correlations and Final State Interactions (FSI) are shown to play a crucial role. We have also investigated the ν induced coherent pion production. We find a strong reduction of the cross section due to the distortion of the pion wave function and the modification of the production mechanisms in the nucleus. The sensitivity of the results to the axial NΔ coupling has been also investigated.

We study the kaon photoproduction associated with the production of the ground state Λ. We investigate the role of K and K* exchange in the t-channel, which can be tested by the photon asymmetry in comparison with experimental data. We find a significant amount of contribution from the one-loop diagram induced by the gauged Wess-Zumino-Witten term for QCD anomaly. This enable us to use coupling constants which are determined in a microscopic way, unlike the previous phenomenological studies where the K* coupling strengths were treated as a free parameter.

We perform the first studies of various inter-quark potentials in SU(3)_c lattice QCD. From the accurate lattice calculation for more than 300 different patterns of three-quark (3Q) systems, we find that the static 3Q potential V_3Q is well described by Y-Ansatz, i.e., the Coulomb plus Y-type linear potential. Quark confinement mechanism in baryons is also investigated in maximally-Abelian projected QCD. We next study the multi-quark potentials V_nQ (n = 4,5) in SU(3)_c lattice QCD, and find that they are well described by the one-gluon-exchange Coulomb plus multi-Y type linear potential, which supports the flux-tube picture even for the multi-quarks. Finally, we study the heavy-heavy-light quark (QQq) potential both in lattice QCD and in a lattice-QCD-based quark model.

We show the first lattice QCD result of the axial charge of N* (1535). We perform the measurements with two flavors of dynamical quarks employing the renormalization-group improved gauge action at β = 1.95 and the mean-field improved clover quark action with the hopping parameters, κ = 0.1375, 0.1390 and 0.1400. In order to avoid signal contaminations by N*(1650), we construct 2 × 2 correlation matrices and diagonalize them so that clear signal separation can be found. The wraparound contributions in the correlator, which can be another source of signal contamination, are eliminated by imposing the Dirichlet boundary condition in the temporal direction. We find that the axial charge of N*(1535) takes a small value, as , which is almost independent of quark masses.

We perform the first study for the bound states of colored scalar particles ϕ (“scalar quarks”) in terms of mass generation with quenched SU(3)_c lattice QCD. We investigate the bound states of ϕ, ϕ^†ϕ and ϕϕϕ (“scalar-quark hadrons”), as well as the bound states of ϕ and quarks ψ, i.e., ϕ^†ψ, ψψϕ and ϕϕψ (“chimera hadrons”). All these new-type hadrons including ϕ have a large mass of several GeV due to large quantum corrections by gluons, even for zero bare scalar-quark mass m_ϕ = 0 at a⁻¹ ~ 1GeV. We find a similar m_ψ-dependence between ϕ^†ψ and ϕϕψ, which indicates their similar structure due to the large mass of ϕ. From this study, we conjecture that all colored particles generally acquire a large effective mass due to dressed gluons.

We study the color confinement of QCD with the Coulomb gauge in lattice simulations. The color-Coulomb instantaneous interaction in color-singlet channel causes a linearly rising potential at large distances. We also estimate the other color-channel forces for two-quark states, i.e. color-octet, color-sextet and color-antitriplet channels. Moreover we investigate the volume dependence of color-nonsinglet potentials on finite lattices.

We investigate the Gribov-Zwanziger scenario in Coulomb gauge QCD using a SU(3) quenched lattice gauge simulation. The ghost propagator diverges in the infrared limit stronger than the free ghost propagator, and the ghost degree of freedom plays a central role in the confinement mechanism in the Coulomb gauge. The infrared divergent ghost dressing function results in the confining color-Coulomb instantaneous interaction. The equal-time transverse gluon propagator is suppressed in the infrared region. Therefore, in the Coulomb gauge, the instantaneous interaction mediated by time-like gluons is responsible for the confining force, and the would-be physical gluons are confined in hadrons.

Chiral monopoles are hedgehoglike structures in local chiral condensates in QCD. These monopoles are (i) made of quark and gluon fields; (ii) explicitly gauge-invariant; (iii) they carry quantized and conserved chromomagnetic charge. We argue that the chiral condensate vanishes in a core of the chiral monopole while the density of these monopoles increases with temperature wiping out the quark condensate in quark-gluon plasma. We suggest that the chiral monopoles are responsible for the chiral symmetry restoration in QCD. We also argue that the chiral monopoles are unlikely to be responsible for confinement of color. Thus, phenomena of the chiral symmetry restoration and the color deconfinement in QCD are not necessarily related to each other and the corresponding transitions may happen at different temperatures.

We present in this talk a recent investigation on the magnetic susceptibility (χ) of the QCD vacuum at finite density, utilizing the nonlocal chiral quark model from the instanton vacuum. We take into account the nonzero current-quark mass (m_q) explicitly to consider the effect of explicit flavor SU(3) symmetry breaking. It turns out that, when we turn on the current-quark mass (m_q ≠ 0), χ becomes smaller, indicating less response to the externally induced electromagnetic field, in comparison to that for m_q = 0.

We perform the first study of baryons in holographic QCD with multi-D-brane system in type IIA superstring theory. The baryon is described as a chiral soliton solution in the four-dimensional meson effective action derived from holographic QCD. We also present a brief review of the holographic model from the viewpoints of recent hadron physics and QCD phenomenologies.

It is widely believed that chiral symmetry is restored not only at high temperatures, but also at high nuclear densities. The drop of the order parameter of the chiral phase transition, the chiral condensate, with density has indeed been calculated in various models and is as such a rather robust result. In this talk I point out that the connection of this property with actual observables is far less clear. For this task a good hadronic description of the primary production of hadrons, their propagation inside the nuclear medium, their decay and the propagation of the decay products through the medium to the detector all have to be treated with equal accuracy and weight. In this talk I illustrate with the examples of ω production and π⁰π⁰ production how important in particular final state interactions are.

We study the chiral transformation properties of all possible local (non-derivative) interpolating field operators for baryons consisting of three quarks with two flavors, assuming good isospin symmetry. We derive and use the relations/identities among the baryon operators with identical quantum numbers that follow from the combined color, Dirac and isospin Fierz transformations. These relations reduce the number of independent baryon operators with any given spin and isospin. The Fierz identities also effectively restrict allowed baryon chiral multiplets. It turns out that the chiral multiplets of the baryons are equivalent to their Lorentz representation.

At a critical finite chemical potential and low temperature QCD undergoes the chiral restoration phase transition. The folklore tradition is that simultaneously hadrons are deconfined and there appears the quark matter. We demonstrate that it is possible to have confined but chirally symmetric hadrons at a finite chemical potential and hence beyond the chiral restoration point at a finite chemical potential and low temperature there could exist a chirally symmetric matter consisting of chirally symmetric but confined hadrons. If it does happen in QCD, then the QCD phase diagram should be reconsidered with obvious implications for heavy ion programs and astrophysics.

The structure of N(1535) is discussed in dynamical and symmetry aspects based on chiral symmetry. We find that the N(1535) in chiral unitary model has implicitly some components other than meson-baryon one. We also discuss the N(1535) in the chiral doublet picture.

We discuss several aspects of the Λ(1405) resonance in relation to the recent theoretical developments in chiral dynamics. We derive an effective single-channel interaction based on chiral SU(3) coupled-channel approach, emphasizing the important role of the πΣ channel and the structure of the Λ(1405) in phenomenology. In order to clarify the structure of the resonance, we study the behavior with the number of colors (N_c) of the poles associated with the Λ(1405), and argue the physical meaning of the renormalization procedure.

We investigate the electric form factors of the nucleon and Roper resonance using a quark-diquark model. We find that the charge radii of the nucleon and Roper resonance are almost the same in size.

The experiment KEK-PS E325 measured e⁺e⁻ and K⁺K⁻ pairs produced in 12 GeV p + A reactions, in order to search for in-medium modification of vector mesons. In the e⁺e⁻ spectra, a significant excess on the low-mass side of the ϕ-meson peak is observed in the very low βγ (= p/m) region of the copper target data. On the other hand when the velocity of ϕ mesons is higher or a smaller target, carbon, is employed, the observed ϕ-meson shapes are consistent with the expected shape in vacuum, both in the e⁺e⁻ and K⁺K⁻ spectra. We have also compared the nuclear mass number dependence of ϕ-meson production between the e⁺e⁻ and K⁺K⁻ decay channels. Using these results, the first experimental limits are obtained for in-medium broadening of the partial decay widths.

In this write-up we summarize the main result of our analysis on the thermal dilepton production rate from the dropping ρ based on the vector manifestation (VM). In the analysis, we showed that the effect of the strong violation of the vector dominance (VD) predicted by the VM, substantially suppresses the dilepton production rate compared with the one predicted by assuming the VD together with the dropping ρ.

Motivated by recent lattice gauge results that the quarkonium does not dissolve at the critical temperature, we report on recent developments in understanding the properties of charmonium states in the quark gluon plasma using perturbative QCD and QCD sum rule approaches. Using lattice results on the energy density and pressure of pure gauge theory as inputs to the operator product expansion in these theories, we find non trivial property changes of heavy quarkonium across the phase transition.

The hyperon-nucleon scattering processes and some dibaryon states are studied both in the chiral SU(3) quark model and in the extended chiral SU(3) quark model by solving the resonating group method (RGM) equation. We find that the short-range interaction could be described either by the one-gluon exchange or by the vector meson exchange for baryon-baryon system.

Photoproduction of vector mesons off nuclei were performed at Jefferson Lab using the CEBAF Large Acceptance Spectrometer (CLAS). The properties of the ρ vector mesons were investigated via their rare leptonic decay to e⁺e⁻. After subtracting the combinatorial background, the ρ meson mass distributions were extracted for each of the targets. We observe no effects on the mass of the ρ meson, some widening in titanium and iron is observed consistent with the collisional broadening.

The electric mean squared radii 〈r²〉_E of Λ(1405) are calculated in the chiral unitary model. We describe the Λ(1405) as a dynamically generated resonance fully in the octet meson and octet baryon scattering. We also consider “Λ(1405)” as a bound state of . For the later “Λ(1405),” we obtain negative and larger absolute value of electric mean squared radius than that of ordinary baryons, which implies that Λ(1405) have structure of widely spread K⁻ around p.

Neutrino is a tiny weakly interacting massive particle, but it has strong impacts on various cosmological and astrophysical phenomena. Neutrinos play a critical role in nucleosynthesis of light-to-heavy mass elements in core-collapse supernovae. The light element synthesis is particularly affected by neutrino oscillation (MSW) effect through the ν-process. We propose first that precise determination of sin² 2θ₁₃ and mass hierarchy can be made by a theoretical study of the observed ⁷Li/¹¹B ratio in stars and presolar grains which are produced from SN ejecta. Theoretical sensitivity in our proposed method is shown to be superior to ongoing long-baseline neutrino experiments for the parameter region 10⁻⁴ ≤ sin²2θ₁₃ ≤ 10⁻². We secondly discuss how to constrain the neutrino mass Σm_ν from precise analysis of cosmic microwave background anisotropies in the presence of primordial magnetic field. We obtain an upper limit Σm_ν < 1.3eV(2σ). Thirdly, we discuss decaying dark-matter particle model in order to solve the primordial lithium problems that the standard Big-Bang nucleosynthesis theory predicts extremely different ⁶Li and ⁷Li abundances from observations.

Nuclear physics is an indispensable input for the investigation of high energy astrophysical phenomena involving compact objects. In this paper I take a gravitational collapse of massive stars as an example and show how the macroscopic dynamics is influenced by the properties of nuclei and nuclear matter. I will discuss two topics that are rather independent of each other. The first one is the interplay of neutrino-nuclei inelastic scatterings and the standing accretion shock instability in the core of core collapse supernovae and the second is concerning the neutrino emissions from black hole formations and their dependence on the equation of state at very high densities. In the latter, I will also demonstrate that future astronomical observations might provide us with valuable information on the equation of state of hot dense matter.

We report the recent developments on the tables of equation of state for dense matter and their influence on core-collapse supernovae and associated neutrino emissions. We study the gravitational collapse of massive stars by the numerical simulations with the tables of equation of state recently developed in relativistic many body frameworks. I discuss whether the equation of state of dense matter can be probed by the properties of neutrino signals from black hole forming supernovae, being different from ordinary neutrino bursts from supernova explosions.

The equation of state (EOS) is calculated for uniform nuclear matter at zero and finite temperatures with the variational method. Making use of uncertainty of the three-body nuclear force, adjustable parameters in the nuclear EOS are tuned so that the Thomas-Fermi calculations for β-stable nuclei with the EOS reproduce the empirical data. The calculated nuclear properties imply that larger symmetry energy of the EOS is preferable to reproduce the empirical β-stability line. The expectation value of the nuclear Hamiltonian caused by the 2π-exchange three-body nuclear force is uncertain and related to the symmetry energy.

We examine the Brown-Rho scaling for meson masses in the strong coupling limit of lattice QCD with one species of staggered fermion. Analytical expression of meson masses is derived at finite temperature and chemical potential. We find that meson masses are approximately proportional to the equilibrium value of the chiral condensate, which evolves as a function of temperature and chemical potential.

The temperature and quark mass dependence of the topological susceptibility is analyzed in a random matrix model. A model combining random matrices and the lowest Matsubara frequency is known to describe the chiral phase transition of QCD qualitatively, but at finite temperature it suppresses the topological susceptibility in the thermodynamic limit by the inverse of the volume. We propose a modified model in which the topological susceptibility at finite temperature behaves reasonably. The modified model reproduces the chiral condensate and the zero-temperature result for the topological susceptibility of the conventional model, and it leads to a topological susceptibility at finite temperature in qualitative agreement with lattice QCD results.

The thermodynamics of a first-order chiral phase transition is considered in the presence of spinodal phase separation using the Nambu-Jona-Lasinio model in the mean field approximation. We focus on the behavior of conserved charge fluctuations. We show that in non-equilibrium the specific heat and charge susceptibilities diverge as the system crosses the isothermal spinodal lines.

In neutron star cores, superfluid state of hyperons such as lambda (Λ) and sigma-minus (Σ⁻) has been shown to realize by a realistic approach. This result importantly supports the idea of nonstandard fast “hyperon cooling” scenario to explain colder class neutron stars observed. However, a less attractive ΛΛ interaction suggested by a double Λ hypernucleus (; “NAGARA” event) leads to a disappearance of Λ superfluidity and thereby the breaking down of the scenario. In this connection, the revival of “Λ superfluidity” due to the ΛΣ⁻ pairing, instead of ΛΛ one, is discussed in a new scheme of “bubble Fermi shell” hypothesis where the matching of two different Fermi surfaces is forced.

We discuss the saturation mechanism for the nuclear matter equation of state in a chiral effective quark theory. The importance of the scalar polarizability of the nucleon is emphasized. The phase transition to color superconducting quark matter is also discussed.

We study the hadron-quark phase transition and antikaon condensation which may occur in the core of massive neutron stars. The relativistic mean field theory is used to describe the hadronic phase, while the Nambu-Jona-Lasinio model is adopted for the quark phase. We find that the hadron-quark phase transition is very sensitive to the models used. The appearance of deconfined quark matter and antikaon condensation can soften the equation of state at high density and lower the maximum mass of neutron stars.

We study the role of the negative-energy nucleon states of relativistic nuclear models in nuclear ground states and excitations. The self-consistent calculation including the negative-energy states are performed by using the derivative expansion in terms of the meson field, which is known to provide a good description of the vacuum fluctuations in nuclear ground states quantitatively. A remarkable effect of the inclusion of the negative-energy contribution into the model is the increase of the nucleon effective mass. In particular, this produces the better description for the isoscalar quadrupole resonances, and essentially different results for the Gamow-Teller resonances.

We study the effect of one-loop corrections from nucleon together with those from meson in the massless linear sigma model, where we perform the Coleman-Weinberg (CW) renormalization procedure in order to obtain the stable effective potential. We also study the non-perturbative and higher loop corrections with fermions and bosons in the Cornwall, Jackiw and Tomboulis (CJT) method.

We briefly summarize the interests in mesic atoms and mesic nuclei in the contemporary hadron-nucleus physics and give a short report on the recent research activities for several meson-nucleus systems.

We have measured the Balmer-series x-rays of kaonic ⁴He atoms using large-area silicon drift x-ray detectors (SDDs) in order to study the low-energy -nucleus strong interaction. The energy of the 3d → 2p transition was determined to be 6467 ± 3(stat) ± 2(syst) eV. The resulting strong-interaction energy-level shift is in agreement with theoretical calculations, thus eliminating a long-standing discrepancy between theory and experiment.

We investigate the properties of η-nucleus interaction by postulating the N*(1535) dominance for η-N system. We evaluate the N*(1535) properties in the nuclear medium using two kinds of chiral models, and find that these two models provide qualitatively different η-nucleus optical potentials reflecting the quite distinct properties of N*(1535) in these chiral models. Especially, in the chiral doublet model, we can expect to have the level crossing between η and N*(1535)-hole which is expected to provide the characteristic features for the optical potential and the formation spectra. We find also that the difference of these models can be seen in the formation cross sections of the η mesic nuclei with (π⁺,p) reaction expected to be performed at J-PARC project.

Formation spectra of model systems excited by reaction are investigated in order to get a theoretical basis for proper interpretation of experimental data concerning kaonic nuclear quasi-bound states. It is argued that experimentally observable kaonic nuclear peak should be regarded as the decaying state introduced by Kapur-Peierls.

We have investigated non-mesonic reactions of the stopped K⁻ on ⁴He in terms of correlations of coincident ΛN pairs. As the result, Λp and Λn branches of the two-nucleon absorption process were clearly observed in the ΛN invariant mass spectra. The spin-isospin dependence of the process was observed for the first time.

The DAΦNE electron-positron collider at the Laboratori Nazionali di Frascati dell'INFN has made available a unique quality negative kaons “beam”. Two experiments, SIDDHARTA and AMADEUS, will use this beam to perform unprecedented precision measurements on kaonic atoms and kaonic nuclei. The scientific cases, together with the experimental setups, are briefly presented in this paper.

We study theoretically the in-flight (K⁻, N) reactions for the formation of systems using the microscopic chiral unitary s-wave amplitude to get deeper physical insights on the expected spectra, and to investigate the experimental feasibility of the reaction at J-PARC facility. We show the missing mass spectra of the (K⁻, N) reactions accompanied by the particle emissions due to absorption in nucleus.

We have investigated the prototype of -nuclear systems, ppK⁻, with a realistic NN potential and effective local potentials based on chiral SU(3) dynamics. Including estimates of theoretical uncertainties, we find that ppK⁻ is not deeply bound, with a total binding energy = 19 ± 3 MeV and mesonic decay width between about 40 and 70 MeV. The component in the ppK⁻ compound is of a similar structure as the two-body quasibound state embedded in the πΣ continuum.

The structure of multi-antikaonic nuclei (MKN), where several K⁻ mesons are bound in the nucleus, is studied in the relativistic mean-field model. A kaonic part of the thermodynamic potential including kaon-nucleon interactions is derived on the basis of chiral symmetry (abbreviated as a chiral model). It is shown that nonperturbative effects from kaons in the chiral model on the properties of the MKN such as the density distributions of nucleons and K⁻ mesons and the binding energy become important since the number of the embedded K⁻ increases.

The formation of a deeply-bound K⁻pp state by the ³He(in-flight K⁻, n) reaction is investigated theoretically in a distorted-wave impulse approximation using the Green's function method. The expected inclusive and semi-exclusive spectra at p_K⁻ = 1.0 GeV/c and θ_n = 0° are calculated for the forthcoming J-PARC E15 experiment. We discuss these spectra with some K⁻-“pp” optical potentials, taking into account the energy-dependence of the imaginary part of the potentials by a phase space suppression factor.

K⁻pn and K⁻pp bound states are searched for at SPring-8/LEPS in the d(γ, K⁺) and d(γ, K⁺π⁻) reactions with photon energies from 1.5 to 2.4 GeV. The data was collected during the 2002-2003 run period utilizing liquid hydrogen and liquid deuterium targets. Using the K⁺ and K⁺π⁻ missing mass spectra from the deuteron, we hope to determine upper limits for K⁻pn and K⁻pp bound state production.

The pion was introduced by Yukawa as the mediator of nucleon-nucleon interaction to bind nucleons in nucleus. Due to its characteristic properties, however, the pion had not be used until recent years for description of nuclei. We present here a newly developed method to treat the pion exchange interaction in nuclei. We study nuclear structure by using the chiral sigma model lagrangian in the relativistic chiral mean field model with projection. The pion develops mean field and provides a magic number effect. We demonstrate also the ability of treating tensor interaction due to pion exchange in terms of tensor optimized shell model.

The significant progresses of the chirality in atomic nuclei are briefly reviewed for both experimental and theoretical sides. Chiral doublet bands beyond one-particle and one-hole coupled with a triaxial rotor as well as the possibilities of new phenomenon MχD are discussed.

We suggest that the three-body force due to the Delta-hole excitation plays a crucial role in determining the neutron drip line of oxygen isotopes. This is one of the consequences of the repulsive effective T=1 force produced by the Delta-hole excitation on the shell evolution. The same mechanism makes effective T=1 interaction more repulsive in general.

Nuclear physics programs recently carried out at the RCNP cyclotron facility have been discussed with emphasis on the two subjects in relation to the chiral symmetry. One is the three-nucleon reactions at intermediate energies and effects of the three-nucleon force, which may be consistently understood in the chiral effective field theory. Another is the high-resolution measurements of spin-isospin excitations and a possibility for explaining the fine-structures in giant resonances by the chiral mean field model.

We investigate the tensor correlations in He and Li isotopes systematically. We propose the tensor-optimized shell model (TOSM) to describe the strong tensor correlation arising from the bare nuclear force in nuclei. Using TOSM for Li isotopes, we investigate the anomalous structures of ^9,10,11Li based on the ⁹Li+n+n model where the ⁹Li cluster is described by TOSM. As a result, the couplings between the tensor correlation in ⁹Li and the extra two neutrons emerge Pauli-blocking, which naturally increases the s² component to develop the halo structure in ¹¹Li. We further describe the short-range correlation arising from the repulsive core in the bare nuclear force by the unitary correlation operator method (UCOM). We propose the new framework of TOSM+UCOM for the nuclear structure study starting from the bare nuclear force.

We study the effect of the tensor force on nuclear structure with mean-field and beyond-mean-field methods. An important correlation induced by the tensor force is two-particle–two-hole (2p2h) correlation, which cannot be treated with a usual mean-field method. To treat the 2p2h tensor correlation, we develop a new framework (charge- and parity-projected Hartree-Fock (CPPHF) method), which is a beyond-mean-field method. We apply the CPPHF method to oxygen isotopes including neutron-rich ones. The potential energy from the tensor force has the same order of magnitude as that from the LS force and becomes smaller with neutron number, which indicates that excess neutrons do not contribute to the 2p2h tensor correlation significantly. We also study the effect of the tensor force on spin-orbit-splitting (ls-splitting) in a neutron-rich fluorine isotope ²³F. The tensor force reduces the ls-splitting for the proton d-orbits by about 3MeV. This effect is important to reproduce the experimental value.

We construct a relativistic framework, charge and parity projected chiral mean field model, which takes into account explicitly a pion-exchange interaction. We take the chiral σ model Lagrangian for the construction of finite nuclei. We discuss several essential points of this framework with respect to explicit description of pionic-correlations, especially high-momentum component, in nuclear ground state wave function. We apply this framework to several even-even nuclei. We found that the pion contribution brings a significant change for nuclear ground state. We found that pion plays a role on the formation of jj-magic structure.

Inspired by recent measurements indicating proton magic number at Z=14 in the vicinity of ⁴²Si, we have employed our relativistic mean-field (RMF) plus state dependent BCS approach for the study of even-even nuclei to obtain magic numbers and to look for nuclei exhibiting weakly bound structures and even halo formation. In our RMF+BCS approach the single particle continuum corresponding to the RMF is replaced by a set of discrete positive energy states for the calculations of pairing energy. It is found that in several nuclei the filling in of low lying single particle resonant state with large angular momentum, even before it becomes a bound state, helps to accommodate more neutrons but with extremely small increase in the binding energy. This gives rise to the occurrence of weakly bound system of neutron rich nuclei.

The approximate energy expression for neutron matter is refined with respect to the tensor forces. The refined energy expression includes the main part of the three-body-cluster kinetic-energy terms caused by tensor correlations appropriately. Furthermore, the new energy expression guarantees necessary conditions on tensor structure functions. Significant improvement is seen in the numerical results of the variational calculation with the refined energy expression for neutron matter.

The theoretical calculations of α-decay half-lives for three kinds of α-emitters (even-even, even-odd, odd-odd nuclei) are systematically reviewed within the framework of the density-dependent cluster model (DDCM). The half-lives of three typical α-emitters (⁸Be, ²¹²Po, and ²⁷⁰Ds) are discussed in detail. The good agreement between experimental and theoretical results shows that DDCM is applicable in the whole mass table from very light nuclei to heavy and superheavy ones.

In a shell-model calculation with traditional effective charges, theoretical B(E2) values are larger than experimental values for neutron-rich carbon isotopes ¹⁶C and ¹⁸C. Using the shell-model with 2ħw excitations in the first order perturbation theory, we investigate the B(E2) values and the effective charges for stable and neutron-rich carbon isotopes.