Tetsuo Hyodo

Effective KN interaction based on chiral SU(3) dynamics

The effective KN interaction based on chiral SU(3) coupled-channel dynamics is derived and its extrapolation below the KN threshold is studied in detail. Starting from the coupled-channel scattering equations, we eliminate the channels other than KN and obtain an effective interaction in the single KN channel. An equivalent local potential in coordinate space is constructed such as to reproduce the full scattering amplitude of the chiral SU(3) coupled-channel framework. We discuss several realistic chiral SU(3)-based models in comparison to reach conclusions about the uncertainties involved. It turns out that, in the region relevant to the discussion of deeply bound K-nuclear few-body systems, the resulting energy-dependent, equivalent local potential is substantially less attractive than the one suggested in previous purely phenomenological treatments.

Chiral SU(3) theory of antikaon-nucleon interactions with improved threshold constraints

K-nucleon interactions are investigated in the framework of coupled-channels dynamics based on the next-to-leading order chiral SU(3) meson-baryon effective Lagrangian. A recent determination of the 1s shift and width of kaonic hydrogen enables us to set accurate constraints on the coupled-channels meson-baryon amplitudes in the strangeness S = 1 sector. Theoretical uncertainties in the subthreshold extrapolation of the coupled-channels amplitudes are discussed. Using this framework, we give predictions for K neutron interactions and for the spectrum of the (1405) resonance. A simplied, eective three-channel model using leading order chiral SU(3) meson-baryon interactions is also constructed for convenient application in K-nuclear few-body calculations.

Variational calculation of the ppK- system based on chiral SU(3) dynamics

The ppK{sup -} system, as a prototype for possible quasibound K nuclei, is investigated using a variational approach. Several versions of energy-dependent effective KN interactions derived from chiral SU(3) dynamics are employed as input, together with a realistic NN potential (Av18). Taking into account theoretical uncertainties in the extrapolations below the KN threshold, we find that the antikaonic dibaryon ppK{sup -} is not deeply bound. With the driving s-wave KN interaction the resulting total binding energy is B(ppK{sup -})=20{+-}3 MeV and the mesonic decay width involving KN{yields}{pi}Y is expected to be in the range 40-70 MeV. Properties of this quasibound ppK{sup -} system (such as density distributions of nucleons and antikaon) are discussed. The {lambda}(1405), as an I=0 quasibound state of K and a nucleon, appears to survive in the ppK{sup -} cluster. Estimates are given for the influence of p-wave KN interactions and for the width from two-nucleon absorption (KNN{yields}YN) processes. With inclusion of these effects and dispersive corrections from absorption, the ppK{sup -} binding energy is expected to be in the range 20-40 MeV, whereas the total decay width can reach 100 MeV but with large theoretical uncertainties.

K−pp system with chiral SU(3) effective interaction

Abstract The K − p p system is investigated using a variational approach with realistic two-body interactions: the Argonne v18 NN potential and an energy dependent K ¯ N effective interaction derived from chiral SU(3) coupled-channel dynamics. Uncertainties in subthreshold extrapolations of the K ¯ N interaction are considered. A weakly bound K − p p state is found, with a binding energy B = ( 19 ± 3 ) MeV substantially smaller than suggested in previous calculations. The decay width Γ ( K − p p → π Σ N ) is estimated to range between about 40 and 70 MeV.

Improved constraints on chiral SU(3) dynamics from kaonic hydrogen

A new improved study of K -proton interactions near threshold is performed using coupledchannels dynamics based on the next-to-leading order chiral SU(3) meson-baryon eective Lagrangian. Accurate constraints are now provided by new high-precision kaonic hydrogen measurements. Together with threshold branching ratios and scattering data, these constraints permit an updated analysis of the complex KN and coupled-channels amplitudes and an improved determination of the K p scattering length, including uncertainty estimates.

Flavor SU(3) breaking effects in the chiral unitary model for meson-baryon scatterings

We examine flavor SU(3) breaking effects on meson-baryon scattering amplitudes in the chiral unitary model. It turns out that the SU(3) breaking, which appears in the leading quark mass term in the chiral expansion, can not explain the channel dependence of the subtraction parameters of the model, which are crucial to reproduce the observed scattering amplitudes and resonance properties.

The nature of the Lambda(1405) resonance in chiral dynamics

Abstract The Λ ( 1405 ) baryon resonance plays an outstanding role in various aspects in hadron and nuclear physics. It has been considered that the Λ ( 1405 ) resonance is generated by the attractive interaction of the antikaon and the nucleon as a quasi-bound state below its threshold decaying into the π Σ channel. Thus, the structure of Λ ( 1405 ) is closely related to the K N interaction which is the fundamental ingredient to study few-body systems with antikaon. In this paper, after reviewing the basic properties of the Λ ( 1405 ) resonance, we introduce the dynamical coupled-channel model which respects chiral symmetry of QCD and the unitarity of the scattering amplitude. We show that the structure of the Λ ( 1405 ) resonance is dominated by the meson–baryon molecular component and is described as a superposition of two independent states. The meson–baryon nature of Λ ( 1405 ) leads to various hadronic molecular states in few-body systems with strangeness which are hadron composite systems driven by the hadronic interactions. We summarize the recent progress in the investigation of the Λ ( 1405 ) structure and future perspective of the physics of the Λ ( 1405 ) resonance.

Compositeness of dynamically generated states in a chiral unitary approach

The structure of dynamically generated states in the chiral unitary approach is studied from a viewpoint of their compositeness. We analyze the properties of bound states, virtual states, and resonances in a single-channel chiral unitary approach, paying attention to the energy dependence of the chiral interaction. We define the compositeness of a bound state using the field renormalization constant which is given by the overlap of the bare state and the physical state in the nonrelativistic quantum mechanics, or by the residue of the bound state propagator in the relativistic field theory. The field renormalization constant enables one to define a normalized quantitative measure of compositeness of the bound state. Applying this scheme to the chiral unitary approach, we find that the bound state generated by the energy-independent interaction is always a purely composite particle, while the energy-dependent chiral interaction introduces the elementary component, depending on the value of the cutoff parameter. This feature agrees with the analysis of the effective interaction by changing the cutoff parameter. A purely composite bound state can be realized by the chiral interaction only when the bound state lies at the threshold or when the strength of the two-body attractive interaction is infinitely large. The natural renormalization scheme, introduced by the property of the loop function and the matching with the chiral low-energy theorem, is shown to generate a bound state which is dominated by the composite structure when the binding energy is small.

Identifying multiquark hadrons from heavy ion collisions.

Identifying hadronic molecular states and/or hadrons with multiquark components either with or without exotic quantum numbers is a long-standing challenge in hadronic physics. We suggest that studying the production of these hadrons in relativistic heavy ion collisions offers a promising resolution to this problem as yields of exotic hadrons are expected to be strongly affected by their structures. Using the coalescence model for hadron production, we find that, compared to the case of a nonexotic hadron with normal quark numbers, the yield of an exotic hadron is typically an order of magnitude smaller when it is a compact multiquark state and a factor of 2 or more larger when it is a loosely bound hadronic molecule. We further find that some of the newly proposed heavy exotic states could be produced and realistically measured in these experiments.

Structure and compositeness of hadron resonances

The structure of the hadron resonances attracts much attention, in association with the recent observations of various exotic hadrons which do not fit well in the conventional picture. These findings urge us to consider various new configurations such as the multiquark states and the hadronic molecules. However, it is a subtle problem to define a proper classification scheme for the hadron structure, and the nonzero decay width of the hadron resonances makes the analysis complicated. In this paper, we summarize the recent developments in the studies of the structure of the hadron resonances, focusing on the notion of the compositeness in terms of the hadronic degrees of freedom.