arXiv subjects

Tetsuo Hyodo

Publications and source records attributed to Tetsuo Hyodo.

At least 37 records · Page 2Linked to original sources

arXiv2025

Effect of eigenstates on spectra in coupled-channel scattering with the chiral unitary model

In recent years, as experimental data on the excited $Ξ(1620)$ and $Ξ(1690)$ states have accumulated, theoretical analyses based on chiral dynamics have also been actively pursued. In this study, we construct theoretical models within the chiral unitary approach to reproduce recent experimental data, and perform a model interpolation to examine the relationship between the poles appearing in different models. We then calculate the invariant mass spectra of the $π^+Ξ^-$ system in the $Ξ_c \to ππΞ$ decay, using the scattering amplitudes obtained from each model, to investigate how the distinct pole structures influence the observable spectrum.

hep-ph↗

arXiv2025

Threshold cusp structures in multi-channel scattering

We study the behavior of the cusp structures focusing on the isospin symmetry breaking effects. The properties of the exotic hadrons are reflected in the shape of the cusp structures. In realistic hadron scatterings, the threshold energies of the isospin partners appear within a small energy region. For a detailed analysis of such systems, it is essential to study the behavior of the cusp structures arising at two closely spaced thresholds. In this work, we introduce a convenient formulation of the scattering amplitude and demonstrate that the cusp structures at two nearby thresholds are related through the isospin symmetry.

hep-ph↗

arXiv2025

Eigenstates in coupled-channel scattering amplitude and their effects on spectrum

In general, discrete eigenstates such as resonances are represented by poles of the scattering amplitude, analytically continued to the complex energy plane. In multi-channel scattering, however, the Riemann surface becomes more complicated, leading to the emergence of various types of poles with distinct characteristics. In this study, we investigate the relationship between poles located on different Riemann sheets and analyze how they influence the observable spectra. In particular, we clarify the effect of the decay channel on the pole trajectory, where an $s$-wave bound state evolves into a resonance via a virtual state. It is shown that the quasibound state pole below the threshold does not continuously connected to the resonance pole above the threshold, and a kind of interchange of poles occurs. As a concrete example, we consider several models based on the chiral unitary approach that describe meson-baryon scattering amplitudes involving the $Ξ(1620)$ and $Ξ(1690)$ resonances. We examine their impact on the $πΞ$ invariant mass distributions in the $Ξ_{c} \to ππΞ$ decay, discussing how the pole structure manifests itself in experimental observables.

hep-ph↗

arXiv2025

Properties of $X(3872)$ from hadronic potentials coupled to quarks

The concept of compositeness is used to quantitatively discuss the hadronic molecular nature in exotic hadrons. In this work, we develop a formulation to explicitly introduce the compact quark state contribution in the hadronic potentials together with the direct four-point interaction. We derive analytic expressions of the compositeness from the effective potential between hadrons when the system has a bound state. Applying this formulation to the $X(3872)$, we examine the variation of the compositeness with respect to the binding energy, energy of $χ_{c1}(2P)$, cutoff momentum, and strength of the direct $D^0\bar{D}^{*0}$ interaction.

hep-ph↗

arXiv2025

Femtoscopy for exotic hadrons and nuclei

In high energy collision experiments with multiple hadron productions, the momentum distribution of the measured hadron pair shows a correlation due to the final state hadron interactions and the quantum statistics. In the past, this femtoscopy technique has been developed to extract the information of the emission source from the momentum correlation functions. Recently, correlation function measurement is utilized also as a new method to determine the hadron interactions. In fact, the ALICE collaboration at LHC measures the correlation functions with various hadron pairs, for which the standard scattering experiment is difficult, providing remarkable progress in the study of the hadron interactions. In this contribution, we introduce the theoretical method to calculate the correlation functions, and present recent results on the study of the antikaon-nucleon interactions and hyperon-nucleus interactions.

hep-ph↗

arXiv2025

Internal structure of $T_{cc}$ and $X(3872)$ by using compositeness

The internal structure of the near-threshold exotic hadrons, $T_{cc}$ and $X(3872)$, are studied by respecting the decay and coupled-channel contributions. The effective field theory model is introduced to calculate the compositeness, the probability of finding the hadronic molecular component. Applying the new interpretation scheme for the complex compositeness of unstable states and using the bare energies of the compact component estimated by the constituent quark model, we find that approximately 50 % of the $T_{cc}$ wavefunction is occupied by the $D^{0}D^{*+}$ molecular component. This indicates that the structure of $T_{cc}$ is primarily dominated by the $D^0D^{*+}$ component, having the nearest threshold. However, other components, such as the isospin partner $D^{*0}D^{+}$ channels, also provide non-negligible contributions. On the other hand, about 90 % of $X(3872)$ is composed of the $D^{0}\bar{D}^{0*}$ molecular component. This is because the non-composite bare state and the charged $D\bar{D}^{*}$ threshold are located relatively far from the $X(3872)$ and contribute very little to its internal structure.

hep-ph↗

arXiv2025

Study of hadron interactions and compositeness

Plenty of hadrons have been established experimentally, yet the nonperturbative nature of the strong interaction complicates a comprehensive understanding of their internal structure, particularly for exotic hadrons that extend beyond conventional mesons and baryons. One prominent candidate for the internal structure of exotic hadrons is the hadronic molecule, a loosely bound system of hadrons analogous to atomic nuclei. Understanding such systems requires precise knowledge of hadron interactions, which traditional scattering experiments struggle to provide, especially in the low-energy region. Recent advances, including precise baryon-baryon interaction measurements, femtoscopy techniques that probe momentum correlations between particles, and first-principles lattice QCD calculations, have significantly improved our understanding of hadron interactions. Here, we review these recent developments, demonstrate the successful application of femtoscopy to antikaon-nucleon interactions, utilize the concept of compositeness to quantify the hadronic molecular component of the Lambda(1405), and discuss both experimental and theoretical prospects, including future studies at J-PARC.

hep-ph↗

arXiv2025

General behavior of near-threshold hadron scattering for exotic hadrons

We discuss the general behavior of the near-threshold scattering amplitude with channel couplings. The signal of the exotic hadrons near the threshold may manifest as a dip structure in the cross section originated from a zero point of the scattering amplitude. Such a dip structure by the zero point cannot be reproduced by the Flatté amplitude which is widely used for the analysis of exotic hadrons, because of the constraints imposed on the Flatté amplitude near the threshold. In this work, we propose the General amplitude which can describe the dip structure near the threshold, in contrast to the Flatté amplitude. Moreover, we numerically study the behavior of the near-threshold cross section in relation to the zero point.

hep-ph↗

arXiv2024

Higher partial waves in femtoscopy

Femtoscopy is recently gaining more attention as a new approach complementary to scattering experiments for constraining hadron-hadron interactions. We discuss the effect of higher partial waves on the two-particle correlation function, which has been neglected in traditional formulae used in the femtoscopy analyses. We consider the partial-wave expansion of the wave function in the Koonin-Pratt formula to give the correction to the correlation function by a sum of the contributions from each partial wave. We also generalize the Lednicky-Lyuboshitz formula, which was originally derived for the s-wave interaction, for higher partial waves. We find a compact representation of the generalized Lednicky-Lyuboshitz formula given by the backward scattering amplitude $f(θ= π)$ and the Fourier-Laplace transform of the relative source function, which gives an insight into the structure of the Lednicky-Lyuboshitz formula and its relation to the optical theorem. We numerically demonstrate the significance of higher partial waves with resonances using the square potential well. Also, the generalized Lednicky-Lyuboshitz formula turned out to be broken for higher partial waves, which suggests the importance of the centrifugal force for the higher partial waves.

nucl-th↗

arXiv2024

Theoretical study on $Λα$ and $Ξα$ correlation functions

We examine the $Λ$-${}^4\mathrm{He}$ ($α$) and $Ξα$ momentum correlation in high-energy collisions to further elucidate the properties of the hyperon-nucleon interactions. For the $Λα$ system, we compare $Λα$ potential models with different strengths at short range. We find that the difference among the models is visible in the momentum correlation from a small-size source. This indicates that the $Λα$ momentum correlation can constrain the property of the $ΛN$ interaction at short range, which plays an essential role in dense nuclear matter. For the $Ξα$ system, we employ the folding $Ξα$ potential based on the lattice QCD $ΞN$ interactions. The $Ξα$ potential supports a Coulomb assisted bound state of ${}^5_Ξ\mathrm{H}$ in the $Ξ^-α$ channel, while the $Ξ^0α$ channel is unbound. To examine the sensitivity of the correlation function to the nature of the $Ξα$ potential, we vary the potential strength simulating stronger and weaker interactions. The result of the correlation function clearly reflects the bound state nature in the $Ξ^-α$ correlation.

nucl-th↗

arXiv2024

Structure of near-threshold resonances with new interpretation scheme of complex compositeness

The nature of near-threshold resonances is quantitatively studied with a new interpretation scheme using the complex compositeness. A difficulty was known in the understanding of the internal structure of unstable resonances because their complex compositeness is not an interpretable measure. To overcome this problem, we develop a new interpretation scheme respecting the ambiguous aspects of the identification of the internal structure of resonances. We then apply the interpretation scheme to the near-threshold resonances slightly above the threshold, described by the effective range expansion. With the new interpretation scheme, we show that near-threshold resonances are dominated by the non-molecular component. Namely, even in the near-threshold region, the nature of resonances is sharply contrasted with bound states whose internal structure is usually molecular dominant.

hep-ph↗

arXiv2024

Femtoscopic study of the $Λα$ interaction

We examine the $Λ$-${}^4\mathrm{He}$ ($α$) momentum correlation in high-energy collisions to elucidate the interaction between Lambdas ($Λ$) and nucleons ($N$). We compare phenomenological $Λα$ potentials with different strengths at short range. In addition to the conventional Gaussian-type potentials, we construct the $Λα$ potentials by substituting the nucleon density distribution in $α$ into the Skyrme-type $Λ$ potentials. We find that the dependence on the employed potential models is visible in the correlation functions from a small-size source. This indicates that the $Λα$ momentum correlation could constrain the property of the $ΛN$ interaction at high densities, which is expected to play an essential role in dense nuclear matter. Also, we verify that the Lednicky-Lyuboshits formula can yield erroneous results for a small-size source with a potential which has a large interaction range, like the $Λα$ system.

nucl-th↗

arXiv2024

General amplitude of near-threshold hadron scattering for exotic hadrons

We discuss the general behavior of the scattering amplitude with channel couplings near the two-body threshold. It is known that the Flatté amplitude, which is often used in the analysis of experimental data involving exotic hadrons, has some constraint in the near-threshold energy region. While the M-matrix gives the general expression of the scattering amplitude, it is not smoothly connected to the Flatté amplitude, due to the property of the determinant of the amplitude in channel space. In this paper, based on the effective field theory, we propose new parametrization of the scattering amplitude which gives the general expression near the threshold and has a well-defined limit reproducing the Flatté amplitude. We show that the nonresonant background contribution exists in the general amplitude even in the first order in the momentum. Finally, we quantitatively evaluate the cross sections by changing the strength of the background contribution. We find that the interference with the background term may induce a dip structure of the cross section near the threshold, in addition to the peak and threshold cusp structures.

hep-ph↗

arXiv2024

Compositeness of $T_{cc}$ and $X(3872)$ by considering decay and coupled-channels effects

The compositeness of weakly bound states is discussed using the effective field theory from the viewpoint of the low-energy universality. We introduce a model with coupling of the single-channel scattering to the bare state, and study the compositeness of the bound state by varying the bare state energy. In contrast to the naive expectation that the near-threshold states are dominated by the molecular structure, we demonstrate that a non-composite state can always be realized even with a small binding energy. At the same time, however, it is shown that a fine tuning is necessary to obtain the non-composite weakly bound state. In other words, the probability of finding a model with the composite dominant state becomes larger with the decrease of the binding energy in accordance with the low-energy universality. For the application to exotic hadrons, we then discuss the modification of the compositeness due to the decay and coupled-channels effects. We quantitatively show that these contributions suppress the compositeness, because of the increase of the fraction of other components. Finally, as examples of near-threshold exotic hadrons, the structures of $T_{cc}$ and $X(3872)$ are studied by evaluating the compositeness. We find the importance of the coupled-channels and decay contributions for the structures of $T_{cc}$ and $X(3872)$, respectively.

hep-ph↗

arXiv2023

Hadron-hadron potentials coupled to quark degrees of freedom for X(3872)

To study the internal structure of the exotic hadron $X(3872)$, considering the coupled-channel potential between quarks and hadrons is necessary because $X(3872)$ is regarded as a mixture state of $c\bar{c}$ and $D^0\bar{D}^{*0}$. In this work, we construct the hadron-hadron potentials coupled to the quark channel and study the properties of the $D^0\bar{D}^{*0}$ potentials for $X(3872)$. In particular, we compare various local approximations by focusing on the scattering phase shifts.

hep-ph↗

arXiv2023

Hadron-hadron potentials coupled to quark degrees of freedom for exotic hadrons

We study the properties of the hadron-hadron potentials and quark-antiquark potentials from the viewpoint of the channel coupling. We demonstrate that, for finite quark masses, the coupling to the two-hadron continuum induces the imaginary part of the quark-antiquark potential, in contrast to the string-breaking phenomena in the static limit. It is also shown that the elimination of the different degrees of freedom induces the nonlocality and energy dependence of the effective potentials. For the obtained nonlocal potentials, we apply two methods of the local approximation proposed previously, the formal derivative expansion and the derivative expansion in the HAL QCD method, by carefully examining the energy dependence of the potential. As an application, we construct a coupled-channel model of $c\bar{c}$ and $D^{0}\bar{D}^{*0}$ to describe $X(3872)$, and discuss the property of the effective $D^{0}\bar{D}^{*0}$ potentials. We confirm that the local approximation by the HAL QCD method works better than the formal derivative expansion also for the energy-dependent potential. At the same time, we show that, in the HAL QCD method, the resulting phase shift is sensitive to the choice of the wavefunction to construct the local potential when the system has a shallow bound state such as $X(3872)$.

hep-ph↗

arXiv2023

Analysis of $Ξ(1620)$ resonance with chiral unitary approach

Recently, the $Ξ(1620)$ resonance has attracted much attention, thanks to detailed experimental data by the Belle and ALICE collaborations. This experimental progress has prepared us to conduct theoretical analyses based on experimental data. In this study, we analyze the $Ξ(1620)$ resonance using the chiral unitary model and discuss the properties of the $Ξ(1620)$ resonance and the $K^-Λ$ scattering length.

hep-ph↗

arXiv2023

Near-threshold hadron scattering with effective field theory

When an exotic hadron locates near the threshold with the channel couplings, the internal structure of the exotic hadron is related to the scattering length. To incorporate the threshold effect, the Flatté amplitude has been often used to determine the scattering length. It is however known that an additional constraint is imposed on the Flatte amplitude near the threshold. We discuss this problem by using the effective field theory for the coupled-channel scattering.

hep-ph↗