Daisuke Jido

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.

Studying Exotic Hadrons in Heavy Ion Collisions

We investigate the possibilities of using measurements in present and future experiments on heavy ion collisions to answer some longstanding problems in hadronic physics, namely identifying hadronic molecular states and exotic hadrons with multiquark components. The yields of a selected set of exotic hadron candidates in relativistic heavy ion collisions are discussed in the coalescence model in comparison with the statistical model. We find that the yield of a hadron is typically an order of magnitude smaller when it is a compact multiquark state, compared to that of an excited hadronic state with normal quark numbers. We also find that some loosely bound hadronic molecules are formed more abundantly than the statistical model prediction by a factor of two or more. Moreover, due to the significant numbers of charm and bottom quarks produced at RHIC and even larger numbers expected at LHC, some of the proposed heavy exotic hadrons could be produced with sufficient abundance for detection, making it possible to study these new exotic hadrons in heavy ion collisions.

Electromagnetic mean squared radii of Λ(1405) in chiral dynamics

Abstract The electromagnetic mean squared radii, 〈 r 2 〉 E and 〈 r 2 〉 M , of Λ ( 1405 ) are calculated in the chiral unitary model. We describe the excited baryons as dynamically generated resonances in the octet meson and octet baryon scattering. We evaluate values of 〈 r 2 〉 E and 〈 r 2 〉 M for the Λ ( 1405 ) on the resonance pole and obtain their complex values. We also consider Λ ( 1405 ) obtained by neglecting decay channels. For the latter case, we obtain negative and larger absolute electric mean squared radius than that of typical ground state baryons. This implies that Λ ( 1405 ) has structure that K − is widely spread around p.

Chiral-symmetry realization for even- and odd-parity baryon resonances

Baryon resonances with even and odd parity are collectively investigated from the viewpoint of chiral symmetry (ChS). We propose a quartet scheme where Deltas and N(*)s with even and odd parity form a chiral multiplet. This scheme gives parameter-free constraints on the baryon masses in the quartet, which are consistent with observed masses with spin 1 / 2,3 / 2,5 / 2. The scheme also gives selection rules in the one-pion decay: The absence of the parity nonchanging decay N(1720)-->piDelta(1232) is a typical example which should be confirmed experimentally to unravel the role of ChS in baryon resonances.

Nuclear bound state of eta'(958) and partial restoration of chiral symmetry in the eta' mass

The in-medium mass of the

KKN molecular state in a three-body calculation

\eta^{\prime}

The

meson is discussed in a context of partial restoration of chiral symmetry in nuclear medium. The

KD

\eta^{\prime}