arXiv subjects

Tetsuo Hyodo

Publications and source records attributed to Tetsuo Hyodo.

At least 109 records · Page 6Linked to original sources

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 $Λ(1405)$.

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arXiv2014

Universal physics of three bosons with isospin

We show that there exist two types of universal phenomena for three-boson systems with isospin degrees of freedom. In the isospin symmetric limit, there is only one universal three-boson bound state with the total isospin one, whose binding energy is proportional to that of the two-boson bound state. With large isospin symmetry breaking, the standard Efimov states of three identical bosons appear at low energies. Both phenomena can be realized by three pions with the pion mass appropriately tuned in lattice QCD simulations, or by spin-one bosons in cold atom experiments. Implication to the in-medium softening of multi-pion states is also discussed.

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arXiv2014

Size measurement of dynamically generated hadronic resonances with finite volume effect

The structures of the hyperon resonance $Λ(1405)$ and the scalar mesons $σ$, $f_{0}(980)$, and $a_{0}(980)$ are investigated based on the coupled-channels chiral dynamics with finite volume effect. The finite volume effect is utilized to extract the coupling constant, compositeness, and mean squared distance between two constituents of a Feshbach resonance state as well as a stable bound state. In this framework, the real-valued size of the resonance can be defined from the downward shift of the resonance pole according to the decreasing finite box size $L$ on a given closed channel. As a result, we observe that, when putting the $\bar{K}N$ and $K\bar{K}$ channels into a finite box while other channels being unchanged, the poles of the higher $Λ(1405)$ and $f_{0}(980)$ move to lower energies while other poles do not show downward mass shift, which implies large $\bar{K}N$ and $K\bar{K}$ components inside higher $Λ(1405)$ and $f_{0}(980)$, respectively. Extracting structures of $Λ(1405)$ and $f_{0}(980)$ in our method, we find that the compositeness of $\bar{K}N$ ($K\bar{K}$) inside $Λ(1405)$ [$f_{0}(980)$] is 0.82-1.03 (0.73-0.97) and the mean distance between two constituents is evaluated as 1.7-1.9 fm (2.6-3.0 fm).

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arXiv2013

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.

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arXiv2013

Structure of Near-Threshold s-Wave Resonances

We study the structure of two-body s-wave bound states as well as resonances in the threshold energy region. We focus on the single-channel scattering where the scattering length and the effective range are given by real numbers. It is shown that, in the energy region where the effective range expansion is valid, the properties of resonances are constrained only by the position of the pole. We find that the compositeness defined through the analytic continuation of the field renormalization constant is pure imaginary and normalized for resonances. We discuss the interpretation of this quantity by examining the structure of the hadron resonance Lambda_c(2595) in the pi Sigma_c scattering. We show that the Lambda_c(2595) resonance requires an unnaturally large effective range and hence it is not likely a pi Sigma_c molecule.

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arXiv2013

Size measurement of dynamically generated resonances with finite boxes

The structure of dynamically generated states is studied from a viewpoint of the finite volume effect. We establish the relation between the spatial size of a stable bound state and the finite volume mass shift. In a single-channel scattering model, this relation is shown to be valid for a bound state dominated by the two-body molecule component. We generalize this method to the case of a quasi-bound state with finite width in coupled-channel scattering. We define the real-valued size of the resonance in a given closed channel using the response to the finite volume effect on the channel. Applying this method to physical resonances we find that Lambda(1405) and f_{0}(980) are dominated by the Kbar N and K Kbar scattering states, respectively, and that the distance between Kbar N (K Kbar) inside Lambda(1405) [f_{0}(980)] is 1.7-1.9 fm (2.6-3.0 fm). The root mean squared radii of Lambda(1405) and f_0(980) are also estimated from the mean distance between constituents.

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arXiv2013

Production of doubly charmed tetraquarks with exotic color configurations in electron-positron collisions

Structure and production of doubly charmed tetraquarks T_cc (cc ubar dbar) are studied from the viewpoint of color configurations. Based on the diquark correlation, the tetraquark T_cc with I(JP)=0(1+) is considered to be stable against strong decay. We discuss that the mixing probability of color antitriplet and sextet cc components in T_cc is suppressed by 1/m_c^2, so the two configurations are separately realized in the heavy quark limit. Utilizing the nonrelativistic QCD framework, we evaluate the production cross sections of T_cc in electron-positron collisions. The momentum dependence of the cross section of color antitriplet is found to be different from that of sextet, which can be used to discriminate the color structure of the T_cc states in experimental measurements.

hep-ph↗

arXiv2013

Recent developments in antikaon-nucleon dynamics

Stimulated by various experimental achievements, the study of Kbar N dynamics now enters a new phase. The two-body Kbar N interaction is largely constrained by recent experimental data, and the nature of the Lambda(1405) resonance is being unveiled by several theoretical analyses. These findings provide a basic tool for applications to Kbar-nuclear systems. We summarize the current status of the Kbar N phenomenology and outline the future direction in this field.

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arXiv2012

Antikaon-nucleon dynamics and its application to few-body systems

We overview the recent progress in the investigation of the antikaon dynamics with single nucleon and with few-body nuclei, based on chiral SU(3) symmetry. We first show how the Lambda(1405) resonance emerges from the coupled-channel Kbar N-pi Sigma interaction. Next, we present the construction of an up-to-date Kbar N interaction in response to the recent measurement of kaonic hydrogen. Finally, we discuss the possibility of the antikaon bound states in nuclei from the perspective of few-body physics.

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arXiv2012

Meson-induced pentaquark productions

Production cross sections of the pentaquark Theta+ baryon in the meson-induced reactions are calculated for JP=1/2+- and 3/2+- cases. Through the comparison with the previous measurements at KEK, several quantum numbers are excluded. The remaining possibilities can be used to cast the upper limit on the Theta+ width, combining with the result from the J-PARC E19 experiment.

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arXiv2012

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

$\bar{K}$-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 $Λ(1405)$ resonance. A simplified, effective three-channel model using leading order chiral SU(3) meson-baryon interactions is also constructed for convenient application in $\bar{K}$-nuclear few-body calculations.

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arXiv2012

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.

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arXiv2011

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

The Lambda(1405) baryon resonance plays an outstanding role in various aspects in hadron and nuclear physics. It has been considered that the Lambda(1405) resonance is generated by the attractive interaction of the antikaon and the nucleon, as a quasi-bound state below the threshold decaying into the pi Sigma channel. Thus, the structure of Lambda(1405) is closely related to the Kbar N interaction which is the fundamental ingredient to study few-body systems with antikaon. In this paper, after reviewing the basic properties of the Lambda(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 Lambda(1405) resonance is dominated by the meson-baryon molecule component and is described as a superposition of two independent states. The meson-baryon nature of Lambda(1405) leads to various hadronic molecule 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 Lambda(1405) structure and future perspective of the physics of the Lambda(1405) resonance.

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arXiv2011

The Lambda* N interaction and two-body bound state based on chiral dynamics

The interaction of Lambda*=Lambda(1405) with a nucleon is studied from the viewpoint of chiral dynamics. We construct the coordinate space Lambda* N potential in the meson-exchange picture, which serves as a fundamental ingredient for the study of the few-body nuclear systems with a Lambda*, the Lambda*-hypernuclei. The coupling constants concerning Lambda* are determined based on the chiral unitary model picture for the meson-baryon scattering where Lambda* is described as a superposition of two resonance poles. Solving the coupled-channel two-body Lambda* N system, we find the higher energy Lambda* N state develops an s-wave quasi-bound state slightly below the threshold in the total spin S=0 channel, which acquires a finite width through the coupling to the lower energy Lambda* N channel. We show important roles of the Kbar exchange contribution to the Lambda* N potential.

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arXiv2011

Hadron resonances with coexistence of different natures

We discuss coexistence/mixing of different natures of hadronic composite (molecule) and elementary (quark-intrinsic) ones in hadron resonances. The discussions here are based on our previous publications on the origin of hadron resonances \cite{Hyodo:2008xr}, exotic $\bar D$ meson-nucleons as hadronic composites containing one anti-heavy quark \cite{Yamaguchi:2011xb}, and the study of $a_1$ as a typical example to show explicitly the mixing of the two different natures \cite{Nagahiro:2011jn}. In all cases, interactions are derived from the chiral dynamics of the light flavor sector. These interactions generate in various cases hadronic composite/molecule states, serving varieties of structure beyond the conventional quark model.

hep-ph↗

arXiv2011

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

A new improved study of K^- - proton interactions near threshold is performed using coupled-channels dynamics based on the next-to-leading order chiral SU(3) meson-baryon effective 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 barK N and pi Sigma coupled-channels amplitudes and an improved determination of the K^- p scattering length, including uncertainty estimates.

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arXiv2011

Internal structure of the Lambda(1405) resonance probed in chiral unitary amplitude

The internal structure of the resonant Lambda(1405) state is investigated based on meson-baryon coupled-channels chiral dynamics. We evaluate Lambda(1405) form factors which are extracted from current-coupled scattering amplitudes in meson-baryon degrees of freedom. Using several probe currents and channel decomposition, we find that the resonant Lambda(1405) state is dominantly composed of widely spread Kbar around N, with escaping pi Sigma component.

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arXiv2011

Determination of the pi Sigma scattering lengths from the weak decays of Lambda_c

The scattering lengths of the pi Sigma systems are key quantities in understanding the structure of the Lambda(1405) resonance and the subthreshold extrapolation of the barK N interaction. We demonstrate that the pi Sigma scattering lengths can be extracted from the threshold cusp phenomena in the weak Lambda_c -> pi pi Sigma decays, analogously with Cabibbo's method for determination of the pi pi scattering length. We show that the substantial cusp effect should be observed in the spectrum, when the pi Sigma interaction in I=0 is strongly attractive to generate a near-threshold singularity, such as a bound state or a virtual state.

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