arXiv subjects

Yasuhiro Yamaguchi

Publications and source records attributed to Yasuhiro Yamaguchi.

At least 19 recordsLinked to original sources

arXiv2026

$D\bar{D}^\ast$-$\pi J/\psi$ scatterings of coupled channels for $Z_c(3900)$ channel

We perform coupled channel analysis for $D \bar D^*$, $J/\psi \pi$ and related meson pairs for the $Z_c(3900)$ channel in an effective model of hadrons and quarks. The model incorporates meson exchange potential such as one pion and $D^{(*)}$ meson exchanges, and quark exchanges. It turns out that the meson exchange potential is small, while the off-diagonal interactions by the quark exchanges at short distances, particularly for transitions between $D\bar D^*$-$J/\psi \pi$ are strong, which plays a main role for the scattering amplitudes for the $Z_c(3900)$ channel, in consistent with the results of the lattice simulations of the HALQCD group.

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arXiv2026

P-wave $c\bar{c}$ meson contributions in exotic hadrons

The nature of the $X(3872)$ and other exotic hadrons has been a subject of extensive investigation. While various theoretical models have been proposed, experimental evidence suggests that the $X(3872)$ may be a mixture state of a hadronic molecule and a $c\bar{c}$ core. In this work, we perform a systematic study of hidden-charm tetraquark candidates $X(3860)$, $X(3872)$, and $Z(3930)$ using a coupled-channel model that incorporates both $c\bar{c}$ states and $D^{(*)}\bar{D}^{(*)}$ hadronic molecular components. The model parameters are fixed to reproduce the masses of the $X(3872)$ and $Z(3930)$, and the resulting framework is used to predict the mass and structure of the $0^{++}$ state associated with the $X(3860)$. Our results support the mixture interpretation of these exotic hadrons, exhibiting strong attractions from the transition potential between $c\bar{c}$ and $D^{(*)}\bar{D}^{(*)}$ components. The molecular component dominates in the $X(3872)$, while the $c\bar{c}$ component plays a more prominent role in the $X(3860)$ and $Z(3930)$.

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arXiv2026

Possible $\bar{D}^{()} \Xi_{cc}^{()}$ and $\Xi_{cc}^{()}\Xi_{cc}^{()}$ molecules as superflavor partners of $T_{cc}$

The doubly charmed tetraquark $T_{cc}$ has been reported by the LHCb experiment in 2022, and a lot of theoretical studies has been conducted. The small binding energy measured from $D^{\ast + }D^0$ threshold indicates that $T_{cc}$ is a $DD^\ast$ molecule. On the other hand, the superflavor symmetry, which relates heavy antiquarks to heavy diquarks, provides a useful framework for predicting the existence of partner exotic hadrons associated with $T_{cc}$. By replacing $\bar{D}^{(*)}$ with $\Xi_{cc}^{(*)}$ within this symmetry, $\bar{D}^{(*)} \Xi_{cc}^{(*)}$ and $\Xi_{cc}^{(*)}\Xi_{cc}^{(*)}$ are expected to form partner structures of $T_{cc}$. In this paper, we investigate bound and resonant states of $\bar{D}^{(*)} \Xi_{cc}^{(*)}$ and $\Xi_{cc}^{(*)}\Xi_{cc}^{(*)}$ based on the one boson exchange potential, where $\pi$, $\rho$, $\omega$ and $\sigma$ are considered as bosons. The cutoff parameter and the coupling constants for $\bar{D}^{(*)} \Xi_{cc}^{(*)}$ and $\Xi_{cc}^{(*)}\Xi_{cc}^{(*)}$ are taken to be the same as those for $T_{cc}$ due to superflavor symmetry. We also discuss the $\sigma$ coupling constant, which is uncertain, dependence of these mass spectra. A lot of bound and resonant states with some quantum numbers are obtained for each $\sigma$ coupling constant, but these mass spectra depend on the $\sigma$ coupling constant significantly.

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arXiv2025

A Study of $T_{cc}(3875)^+$ Nature : Compact v.s. Molecule

A central question in exotic-hadron physics is their internal structure whether these states are loosely bound hadronic molecules or compact multiquark configurations. To shed light on this issue, we develop a model that incorporates mixing between hadronic-molecular and compact multiquark components. We then apply this framework to the specific case of the $T_{cc}(3875)^+$ and analyze the peak structure in the $D^0D^0\pi^+$ invariant-mass spectrum reported by LHCb. We find that a scenario based on a predominantly compact tetraquark provides the best fitted solution which can explain the $T_{cc}(3875)^+$. We also find that the model admits two more solutions of comparable quality, both of which imply that the $T_{cc}(3875)^+$ is a molecular state: (1) the $T_{cc}(3875)^+$ is a $D^{*+}D^0$ molecule and there is a $D^{*0}D^+$ molecular state in addition; (2) the $T_{cc}(3875)^+$ is a $D^{*0}D^+$ molecule and an aditional $D^{*+}D^0$ molecular state is found below $D^0D^0\pi^+$ threshold. These molecular states are not simple $I = 0$ states, but mixtures of $I = 0$ and $I = 1$ states. We show that all three scenarios are also consistent with the experimentally observed near-threshold $D^0D^0$ and $D^0D^+$ invariant-mass distributions.

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arXiv2025

Hadronic Molecules and $\chi_{cJ}(2P)$ Coupled States

We investigate hidden-charm exotic mesons based on a coupled-channel framework, where the physical states are described as superpositions of a compact $c\bar c$ core (identified with the $\chi_{cJ}(2P)$ states) and hadronic components such as $D^{(*)}\bar D^{(*)}$. We incorporate meson exchange potentials to describe hadron-hadron interactions and determine model parameters to reproduce the observed masses of $X(3872)$ and $Z(3930)$. The model also predicts a $0^{++}$ bound state consistent with the $X(3860)$. The internal structure is found to be predominantly molecular for the $X(3872)$, while the $X(3860)$ and $Z(3930)$ have larger $c\bar{c}$ components. The coupling between $c\bar{c}$ cores and hadronic components plays a crucial role in generating these states. The resulting wave functions provide insight into the internal structure and decay properties of these exotic states.

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arXiv2025

Di-$J/\psi$ structures from the quark Pauli-blocking effect

The double-charmonium scattering states such as $J/\psi J/\psi$, $\eta_cJ/\psi$, and $\eta_c\eta_c$ are investigated by a simplified quark cluster model. It is found that the quark Pauli-principle over the $c\bar c c\bar c$ system causes a rapid increase and a node in the two-meson phase shifts. The increase is not large enough to be regarded as a resonance, but if it is seen experimentally, that is most likely the quark Pauli-blocking effect.

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arXiv2025

Hidden-Charm Tetraquarks in a Mixture Model: Coupled-Channel Analysis with $c\bar{c}$ and Hadronic Molecular Components

The nature of the $X(3872)$ and other exotic hadrons has been a subject of extensive investigation since the first observation of the $X(3872)$ in 2003. While various theoretical models have been proposed, including hadronic molecular and compact tetraquark interpretations, some experimental evidence suggests that the $X(3872)$ may be a mixture state of a hadronic molecule and a $c\bar{c}$ core. In this work, we perform a systematic study of the hidden-charm tetraquark candidates $X(3860)$, $X(3872)$, and $Z(3930)$ using a coupled-channel model that incorporates both $c\bar{c}$ states and $D^{(*)}\bar{D}^{(*)}$ hadronic molecular components. The $c\bar{c}$ sector is described based on the constituent quark model predictions for the $\chi_{cJ}(2P)$ ($J = 0, 1, 2$) states, while the meson-meson interactions are modeled using pseudoscalar and vector meson exchange potentials. The model parameters are fixed to reproduce the masses of the $X(3872)$ and $Z(3930)$, and the resulting framework is used to predict the mass and structure of the $J^{PC} = 0^{++}$ state associated with the $X(3860)$. Our results support the mixture interpretation of these exotic hadrons, exhibiting strong attractions from the transition potential between $c\bar{c}$ and $D^{(*)}\bar{D}^{(*)}$ components. The molecular component is found to dominate in the $X(3872)$, while the $c\bar{c}$ component plays a more prominent role in the $X(3860)$ and $Z(3930)$.

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arXiv2025

Analysis of bound and resonant states of doubly heavy tetraquarks with spin $J\leq 2$

Recently, a number of exotic hadrons have been reported in the experiments, and most of these states lie slightly below the threshold. Therefore, these states are considered to be hadronic molecules composed of mesons or baryons. In 2022, the doubly charmed tetraquark $T_{cc}$ was reported by the LHCb experiment, which is considered to be composed of two heavy quarks and two light antiquarks, and located slightly below the $DD^\ast$ threshold. The observation motivates us to study the bound and resonant states of the doubly heavy tetraquarks as two meson systems. We employ the one boson exchange potential as an interaction between two mesons, where one free parameter has been determined to reproduce $T_{cc}$ reported by the LHCb experiment. In our previous work, bound states of $D^{(\ast)}D^{(\ast)}$ and $B^{(\ast)}B^{(\ast)}$ molecules were studied, where we respected the heavy quark spin symmetry (HQS). Using the same framework, we study not only bound but also resonant states with $J\leq 2$ in this paper. Furthermore, we discuss the HQS partner structures of $T_{cc}$ and $T_{bb}$ obtained in our study by introducing the light cloud basis.

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arXiv2024

Mass and decay width of $T_{ccs}$ from symmetries

We analyze the mass and width of the doubly heavy tetraquark $T_{ccs}$ composed of a heavy diquark and a light-quark cloud with strangeness with assuming that a color antitriplet heavy diquark is a dominant component of the doubly charmed tetraquarks $T_{cc}$ and $T_{ccs}$. We construct an effective Lagrangian for masses of heavy hadrons based on the superflavor symmetry between the doubly heavy tetraquarks and the singly heavy baryons by including the terms that simultaneously break the heavy-quark and light-flavor symmetries, and predict the mass of $T_{ccs}$ as $M(T_{ccs}) = 4047\pm11$\,MeV. The comparison of this prediction with future experimental observation will give a clue to understand the color structure of the heavy diquark. We also predict the mass of $Ω_{cc}$ as $M(Ω_{cc}) = 3706^{+14}_{-15}\,$MeV. We next calculate the decay width of $T_{ccs}$, based on solely the light-flavor symmetry, as $Γ(T_{ccs}) = 42\pm 24$\,MeV.

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arXiv2024

X(3872) revisited: the roles of OPEP and the quark degrees of freedom

The $X(3872)$ is investigated by employing the quark-hadron hybrid model, that consists of the $c\bar c$ core, $D^{(*)}\bar D{}^*$, $J/ψω$, and $J/ψρ$ two-meson states. Due to the attraction from the $c\bar c$-$D\bar D{}^*$ coupling and from the OPEP tensor coupling, a very thin peak can appear at the $D^{0}\bar D{}^{*0}$ threshold. The energy of the corresponding pole of the scattering matrix is $E=(+0.06-0.14i)$ MeV, which is on the physical sheet and above the threshold, the same as the one of the poles from the LHCb data analysis.

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arXiv2024

The impact of quark many-body effects on exotic hadrons

We investigate the exotic hadrons consisting of two light quarks and two heavy antiquarks, $(q\bar Q)$-$(q\bar Q)$. The spin-dependent term between quarks is known to give an attraction to the $ud$ spin-0 component in the isospin-0 $u\bar c d\bar c$ system, $T_{cc}$. However, the said component also gets a repulsion from the partial Pauli-blocking. By the dynamical calculation with a simplified quark model, we discuss that the competition of the two effects leads to a shallow bound state for $T_{cc}$, which is preferred from the experiment, and a deep bound state for $T_{bb}$.

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arXiv2023

Analysis of $T_{cc}$ and $T_{bb}$ based on the hadronic molecular model and their spin multiplets

${T_{cc}(cc\bar{u}\bar{d})}^{+}$ has been reported by the LHCb experiment in 2022. The analysis using the Breit-Wigner parametrization found the small binding energy, $0.273$ MeV, which is measured from the threshold of $D^{*+}D^{0}$. In this paper, we consider $T_{cc}$ as a $DD^*$ hadronic molecule as a deuteron-like state. The one boson exchange model is employed as for the heavy meson interactions, where we determine the cut-off parameter $Λ$ to reproduce the reported binding energy of $T_{cc}$ with $I(J^P)=0(1^+)$. We discuss the properties of the bound state, and also search for $T_{cc}$ with the quantum numbers other than $0(1^{+})$. Futhermore, we analyze $T_{bb}$ as a bottom counterpart of $T_{cc}$, which involves two bottom quarks, and obtain several bound states. Finally we consider the light-cloud basis for wave functions of the doubly heavy tetraquarks in the heavy quark limit. Using the basis, we find the spin multiplets of their bound states, indicating the spin structures of diquarks in $T_{cc}$ and $T_{bb}$ with the finite quark masses.

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arXiv2023

Analysis of $DD^$ and $\bar{D}^{()}Ξ_{cc}^{(*)}$ molecule by one boson exchange model based on Heavy quark symmetry

Numerous exotic hadrons with heavy quarks have been reported in the experiments. In such states, symmetries of heavy quarks are considered to play a significant role. In particular, the superflavor symmetry, or also called the heavy quark anti-diquark symmetry is one of the interesting symmetries, which links a quark $Q$ to an anti-diquark $\bar{Q}\bar{Q}$ having the same color representation as $Q$. In this paper, we study a $\bar{D}Ξ_{cc}$ molecular state as a superflavor partner of the doubly charm tetraquark $T_{cc}$ reported by LHCb recently. $T_{cc}$ locating slightly below the $DD^*$ threshold is a candidate of the hadronic molecule. Thus by replacing the singly charm meson $D^{(*)}$ with the doubly charm baryon $Ξ_{cc}^{(*)}$, superflavor symmetry predicts the existence of the $\bar{D}^{(*)}Ξ_{cc}^{(*)}$ bound state. We employ the one boson exchange model respecting with the heavy quark spin symmetry where the parameter is obtained to reproduce the $T_{cc}$ binding energy. We apply this model with superflavor symmetry to the $\bar{D}^{(*)}Ξ_{cc}^{(*)}$ molecule and predict a bound state with $I(J^P) = 0(\frac{1}{2}^-)$. If the pentaquark state corresponding to $\bar{D}^{(*)} Ξ_{cc}^{(*)}$ molecular state is observed in future experiments as predicted in this work, it is more likely that $T_{cc}$ is a $DD^*$ molecular state.

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arXiv2022

Open charm and bottom meson-nucleon potentials à la nuclear force

We discuss the interaction of an open heavy meson ($\bar{D}$ and $\bar{D}^{\ast}$ for charm or $B$ and $B^{\ast}$ for bottom) and a nucleon ($N$) by considering the $π$, $σ$, $ρ$, and $ω$ exchange potentials. We construct a potential model by respecting chiral symmetry for light quarks and spin symmetry for heavy quarks. Model parameters are adjusted by referring the phenomenological nuclear (CD-Bonn) potentials reproducing the low-energy $NN$ scatterings. We show that the resulting interaction may accommodate $\bar{D}N$ and $BN$ bound states with quantum number $I(J^{P})=0(1/2^{-})$, and a $BN$ bound state with $I(J^{P})=1(1/2^{-})$. We find that, in the present potential model, the $σ$ exchange potential plays an important role.

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arXiv2022

Rich structure of the hidden-charm pentaquarks near threshold regions

The recent abundant observations of pentaquarks and tetraquarks by high-energy accelerator facilities indicate the realization of the conjecture by Gell-Mann and Zweig, and by De Rujula, Georgi and Glashow [1-3]. We construct a coupled-channel model for the hidden-charm pentaquarks with strangeness whose quark content is $udsc \bar c$, $P_{cs}$, described as $ Λ_c \bar{D}_s^{(*)}, Ξ_c^{('*)} \bar{D}^{(*)}$ molecules coupled to the five-quark states. These molecules are formed by the suitable cooperation of heavy quark and chiral symmetries. We reproduce the experimental mass and quantum numbers $J^P$ of $P_{cs}(4338)$ for which LHCb has just announced the discovery. We make other predictions for new $P_{cs}$ states as molecular states near threshold regions that can be studied by LHCb.

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arXiv2022

Substructure of Multiquark Hadrons (Snowmass 2021 White Paper)

In recent years there has been a rapidly growing body of experimental evidence for existence of exotic, multiquark hadrons, i.e. mesons which contain additional quarks, beyond the usual quark-antiquark pair and baryons which consist of more than three quarks. In all cases with robust evidence they contain at least one heavy quark Q=c or b, the majority including two heavy quarks. Two key theoretical questions have been triggered by these discoveries: (a) how are quarks organized inside these multiquark states -- as compact objects with all quarks within one confinement volume, interacting via color forces, perhaps with an important role played by diquarks, or as deuteron-like hadronic molecules, bound by light-meson exchange? (b) what other multiquark states should we expect? The two questions are tightly intertwined. Each of the interpretations provides a natural explanation of parts of the data, but neither explains all of the data. It is quite possible that both kinds of structures appear in Nature. It may also be the case that certain states are superpositions of the compact and molecular configurations. This Whitepaper brings together contributions from many leading practitioners in the field, representing a wide spectrum of theoretical interpretations. We discuss the importance of future experimental and phenomenological work, which will lead to better understandingof multiquark phenomena in QCD.

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arXiv2021

Quark level and hadronic contributions to the electric dipole moment of charged leptons in the standard model

We evaluate the electric dipole moment of charged leptons in the standard model, where the complex phase of the Cabibbo-Kobayashi-Maskawa matrix is the only source of CP violation. We first prove that, at the quark-gluon level, it is suppressed by a factor of $m_b^2 m_c^2 m_s^2$ at all orders of perturbation due to the Glashow-Iliopoulos-Maiani mechanism. We then calculate the hadronic long distance contribution generated by vector mesons at one-loop level. The $|ΔS|=1$ weak hadronic interaction is derived using the factorization, and the strong interaction is modeled by the hidden local symmetry framework. We find that the electric dipole moments of charged leptons obtained from this hadronic mechanism are much larger than the perturbative four-loop level quark-gluon process, by several orders of magnitude.

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arXiv2021

Large long-distance contributions to the electric dipole moments of charged leptons in the standard model

We reevaluate the electric dipole moment (EDM) of charged leptons in the standard model using hadron effective models. We find unexpectedly large EDM generated by the hadron level long-distance effect, $d_e = { 5.8 \times 10^{-40} }$, $d_μ= { 1.4 \times 10^{-38}}$, and $d_τ= { -7.3 \times 10^{-38} }$ ecm, with an error bar of 70\%, exceeding the conventionally known four-loop level elementary contribution by several orders of magnitude.

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