arXiv subjects

Yasuhiro Yamaguchi

Publications and source records attributed to Yasuhiro Yamaguchi.

At least 37 records · Page 2Linked to original sources

arXiv2020

Heavy hadronic molecules with pion exchange and quark core couplings: a guide for practitioners

We discuss selected and important features of hadronic molecules as one of promising forms of exotic hadrons near thresholds. Using examples of $D \bar D^*$ systems such as $X(3872)$ and $Z_c$, emphasis is put on the roles of the one pion exchange interaction between them and their coupling to intrinsic quark states. Thus hadronic molecules emerge as admixtures of the dominant long-range hadron structure and short-range quark structure. For the pion exchange interaction, properties of the tensor force are analyzed in detail. More coupled channels supply more attractions, and heavier constituents suppress kinetic energies, providing more chances to form hadronic molecules of heavy hadrons. Throughout this article, we show details of basic ideas and methods.

hep-ph↗

arXiv2020

Emergent spin-$1$ Haldane gap and ferroelectricity in a frustrated spin-$1/2$ ladder

We report experimental and theoretical evidence that Rb$_2$Cu$_2$Mo$_3$O$_{12}$ has a nonmagnetic tetramer ground state of a two-leg ladder comprising antiferromagnetically coupled frustrated spin-$1/2$ chains and exhibits a Haldane spin gap of emergent spin-1 pairs. Three spin excitations split from the spin-1 triplet by a Dzyaloshinskii-Moriya interaction are identified in inelastic neutron-scattering and electron spin resonance spectra. A tiny magnetic field generates ferroelectricity without closing the spin gap, indicating a novel class of ferroelectricity induced by a vector spin chirality order.

cond-mat.str-el↗

arXiv2020

$P_c$ pentaquarks with chiral tensor and quark dynamics

We investigate the hidden-charm pentaquarks as superpositions of $Λ_c \bar{D}^{(*)}$ and $Σ_c^{(*)} \bar{D}^{(*)}$ (isospin $I = 1/2$) meson-baryon channels coupled to a $uudc\bar{c}$ compact core by employing an interaction satisfying the heavy quark and chiral symmetries. Our model can consistently explain the masses and decay widths of $P_c^+(4312)$, $P_c^+(4440)$ and $P_c^+(4457)$ with the dominant components of $Σ_c \bar D$ and $Σ_c \bar D^\ast$ with spin parity assignments $J^P = 1/2^{-}, 3/2^{-}$ and $1/2^{-}$, respectively. We analyze basic properties of the $P_c$'s such as masses and decay widths, and find that the mass ordering is dominantly determined by the quark dynamics while the decay widths by the tensor force of the one-pion exchange.

hep-ph↗

arXiv2019

Heavy quark spin multiplet structure of $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$

Very recently, the LHCb collaboration has reported the new result about the hidden-charm pentaquarks: $P_c(4312)$ near the $\bar{D}Σ_c$ threshold, and $P_c(4440)$ and $P_c(4457)$ near $\bar{D}^*Σ_c$ threshold. We study the heavy quark spin (HQS) multiplet structures of these newly $P_c$ pentaquarks under the heavy quark spin symmetry based on the hadronic molecular picture. We point out that $P_c(4312)$ is the $J^P = 1/2^-$ member of an HQS triplet, and $P_c(4440)$ and $P_c(4457)$ are the $J^P = 3/2^-$ member of the HQS triplet and an HQS singlet with $J^P = 3/2^-$. Namely, the $P_c(4312)$ and one of $P_c(4440)$ and $P_c(4457)$ belong to an HQS triplet. The HQS multiplet structure predicts the existence of $J^P = 5/2^-$ state near $\bar{D}^\astΣ_c^\ast$ threshold.

hep-ph↗

arXiv2019

Heavy quark spin multiplet structure of $P_c$-like pentaquark as P-wave hadronic molecular state

We study the heavy quark spin (HQS) multiplet structure of P-wave $Q\bar{Q}qqq$-type pentaquarks treated as molecules of a heavy meson and a heavy baryon. We define the light-cloud spin (LCS) basis decomposing the meson-baryon spin wavefunction into the LCS and HQS parts. Introducing the LCS basis, we find HQS multiplets classified by the LCS; five HQS singlets, two HQS doublets, and three HQS triplets. We construct the one-pion exchange potential respecting the heavy quark spin and chiral symmetries to demonstrate which HQS multiplets are realized as a bound state. By solving the coupled channel Schrödinger equations, we study the heavy meson-baryon systems with $I=1/2$ and $J^P=(1/2^+, 3/2^+, 5/2^+, 7/2^+)$. The bound states which have same LCS structure are degenerate at the heavy quark limit, and the degeneracy is resolved for finite mass. This HQS multiplet structure will be measured in the future experiments.

hep-ph↗

arXiv2018

Heavy quark spin multiplet structure of $\bar{P}^{()}Σ_Q^{()}$ molecular states

We study the structure of heavy quark spin (HQS) multiplets for heavy meson-baryon molecular states in a coupled system of $\bar{P}^{(*)}Σ_{Q}^{(*)}$, with constructing the one-pion exchange potential with S-wave orbital angular momentum. Using the light cloud spin basis, we find that there are four types of HQS multiplets classified by the structure of heavy quark spin and light cloud spin. The multiplets which have attractive potential are determined by the sign of the coupling constant for the heavy meson-pion interactions. Furthermore, the difference in the structure of light cloud spin gives the restrictions of the decay channel, which implies that the partial decay width has the information for the structure of HQS multiplets. This behavior is more likely to appear in hidden-bottom sector than in hidden-charm sector.

hep-ph↗

arXiv2018

Hidden-charm and bottom meson-baryon molecules coupled with five-quark states

In this paper, we investigate the hidden-charm pentaquarks as $\bar{D}^{(\ast)}Λ_{\rm c}$ and $\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$ molecules coupled to the five-quark states. Furthermore, we extend our calculations to the hidden-bottom sector. The coupling to the five-quark states is treated as the short range potential, where the relative strength for the meson-baryon channels is determined by the structure of the five-quark states. We found that resonant and/or bound states appear in both the charm and bottom sectors. The five-quark state potential turned out to be attractive and, for this reason, it plays an important role to produce these states. In the charm sector, we need the five-quark potential in addition to the pion exchange potential in producing bound and resonant states, whereas, in the bottom sector, the pion exchange interaction is strong enough to produce states. Thus, from this investigation, it emerges that the hidden-bottom pentaquarks are more likely to form than their hidden-charm counterparts; for this reason, we suggest that the experimentalists should look for states in the bottom sector.

hep-ph↗

arXiv2017

Mesic nuclei with a heavy antiquark

The binding system of a hadron and a nucleus is a topic of great interest for investigating the hadron properties. In the heavy-flavor region, the attraction between a $P(=\bar{D},B)$ meson and a nucleon $N$ can appear, where the $PN-P^\ast N$ mixing plays an important role in relation to the heavy-quark spin symmetry. The attraction can produce exotic heavy mesic nuclei that are stable against the strong decay. We study an exotic system where the $\bar{D}$ ($B$) meson and nucleus are bound. The meson-nucleus interaction is given by a folding potential with single-channel $PN$ interaction and the nucleon number distribution function. By solving the Schrödinger equations of the heavy meson and the nucleus, we obtain several bound and resonant states for nucleon number $A=16,\dots,208$. The results indicate the possible existence of exotic mesic nuclei with a heavy antiquark.

nucl-th↗

arXiv2017

Heavy Hadrons in Nuclear Matter

Current studies on heavy hadrons in nuclear medium are reviewed with a summary of the basic theoretical concepts of QCD, namely chiral symmetry, heavy quark spin symmetry, and the effective Lagrangian approach. The nuclear matter is an interesting place to study the properties of heavy hadrons from many different points of view. We emphasize the importance of the following topics: (i) charm/bottom hadron-nucleon interaction, (ii) structure of charm/bottom nuclei, and (iii) QCD vacuum properties and hadron modifications in nuclear medium. We pick up three different groups of heavy hadrons, quarkonia ($J/ψ$, $Υ$), heavy-light mesons ($D$/$\bar{D}$, $\bar{B}$/$B$) and heavy baryons ($Λ_{c}$, $Λ_{b}$). The modifications of those hadrons in nuclear matter provide us with important information to investigate the essential properties of heavy hadrons. We also give the discussions about the heavy hadrons, not only in nuclear matter with infinite volume, but also in atomic nuclei with finite baryon numbers, to serve future experiments.

hep-ph↗

arXiv2017

Quark mass dependence of H-dibaryon in $ΛΛ$ scattering

We study the quark mass dependence of the H-dibaryon in the strangeness $S=-2$ baryon-baryon scattering. A low-energy effective field theory is used to describe the coupled-channel scattering, in which the quark mass dependence is incorporated so as to reproduce the lattice QCD data by the HAL QCD collaboration in the SU(3) limit. We point out the existence of the Castillejo-Dalitz-Dyson (CDD) pole in the $ΛΛ$ scattering amplitude below the threshold in the SU(3) limit, which may cause the Ramsauer-Townsend effect near the $NΞ$ threshold at the physical point. The H-dibaryon is unbound at the physical point, and a resonance appears just below the $NΞ$ threshold. As a consequence of the coupled-channel dynamics, the pole associated with the resonance is not continuously connected to the bound state in the SU(3) limit. Through the extrapolation in quark masses, we show that the unitary limit of the $ΛΛ$ scattering is achieved between the physical point and the SU(3) limit. We discuss the possible realization of the "H-matter" in the unphysical quark mass region.

hep-ph↗

arXiv2016

Quark mass dependence of H-dibaryon

The H-dibaryon is the exotic multiquark state with baryon number 2 and strangeness $-2$. The existence of the deeply bound H-dibaryon is excluded by the observation of the double hypernuclei. However the recent Lattice QCD simulations have found the bound state below the $ΛΛ$ threshold with large quark masses by HALQCD and NPLQCD collaborations. In this talk, the quark mass dependence of the H-dibaryon mass is discussed using the pionless effective field theory (EFT) where a bare H-dibaryon field is coupled with two-baryon states. We determine the parameters in this theory by fitting the recent Lattice QCD results in the SU(3) limit. As a result, we obtain the attractive scattering length at the physical point where the H-dibaryon is unbound.

hep-ph↗

arXiv2016

Hidden-charm pentaquarks as a meson-baryon molecule with coupled channels for $\bar{D}^{(\ast)}Λ_{\rm c}$ and $\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$

The recent observation of two hidden-charm pentaquark states by LHCb collaborations prompted us to investigate the exotic states close to the $\bar{D}Λ_{\rm c}$, $\bar{D}^{\ast}Λ_{\rm c}$, $\bar{D}Σ_{\rm c}$, $\bar{D}Σ^{\ast}_{\rm c}$, $\bar{D}^{\ast}Σ_{\rm c}$ and $\bar{D}^{\ast}Σ^{\ast}_{\rm c}$ thresholds. We therefore studied the hadronic molecules that form the coupled-channel system of $\bar{D}^{(\ast)}Λ_{\rm c}$ and $\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$. As the heavy quark spin symmetry manifests the mass degenerations of $\bar{D}$ and $\bar{D}^\ast$ mesons, and of $Σ_{\rm c}$ and $Σ^\ast_{\rm c}$ baryons, the coupled channels of $\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$ are important in these molecules. In addition, we consider the coupling to the $\bar{D}^{(\ast)}Λ_{\rm c}$ channel whose thresholds are near the $\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$ thresholds, and the coupling to the state with nonzero orbital angular momentum mixed by the tensor force. This full coupled channel analysis of $\bar{D}^{(\ast)}Λ_{\rm c}-\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$ with larger orbital angular momentum has never been performed before. By solving the coupled-channel Schrödinger equations with the one meson exchange potentials that respected to the heavy quark spin and chiral symmetries, we studied the hidden-charm hadronic molecules with $I(J^P)=1/2(3/2^\pm)$ and $1/2(5/2^\pm)$. We conclude that the $J^P$ assignment of the observed pentaquarks is $3/2^+$ for $P^+_{\rm c}(4380)$ and $5/2^-$ for $P^+_{\rm c}(4450)$, which is agreement with the results of the LHCb analysis. In addition, we give predictions for other $J^P=3/2^\pm$ states at 4136.0, 4307.9 and 4348.7 MeV in $J^P=3/2^-$, and 4206.7 MeV in $J^P=3/2^+$, which can be further investigated by means of experiment.

hep-ph↗

arXiv2015

Holographic Heavy Quark Symmetry

We investigate the heavy quark spin symmetry, i.e. the mass degeneracy of pseudo-scalar and vector quarkonia at heavy quark limit, by using the gauge/gravity correspondence. We allow generic D3-like geometry with a flavor D7-brane, to avoid supersymmetric mass degeneracy. For geometries admitting physical QCD-like properties, we find that the mass degeneracy is generically achieved in a good accuracy, up to a few percent mass splitting. We also compute spectra of excited quarkonia states, and discuss comparisons with experiments and quark-model calculations.

hep-th↗

arXiv2014

Exotic dibaryons with a heavy antiquark

We discuss the possible existence of exotic dibaryons with a heavy antiquark, being realized three-body systems, Dbar^(*)NN and B^(*)NN. These are genuinely exotic states with no quark-antiquark annihilation. We consider the heavy quark spin and chiral symmetries, and introduce the one pion exchange potential between a Dbar^(*) (B^(*)) meson and a nucleon N. As for the NN interaction, we employ the Argonne v^\prime_8 potential. By solving the coupled-channel equations for PNN and P^* NN (P^(*)=Dbar^(*) and B^(*)), we find bound states for (I,J^P)=(1/2,0^-) as well as resonant states for (I,J^P)=(1/2,1^-) both in Dbar^(*)NN and B^(*)NN systems. We also discuss the heavy quark limit, and find that the spin degeneracy is realized in the bound states with (I,J^P)=(1/2,0^-) and (1/2,1^-).

nucl-th↗

arXiv2013

Hadronic molecules for charmed and bottom baryons near thresholds

We study hadronic molecules formed by a heavy meson and a nucleon, DN and D*N (BbarN and Bbar*N) systems. Respecting the heavy quark symmetry and chiral symmetry, we consider the DN-D*N (BbarN-Bbar*N$) mixing induced by the one boson exchange potential including the tensor force. We find many bound and resonant states with J^P=1/2^\pm, 3/2^\pm, 5/2^\pm and 7/2^- in isospin singlet channels, while only a few resonant states with J^P=1/2^- in isospin triplet channels. The analysis of DN and D*N (BbarN and Bbar*N) molecules will be useful to study mass spectra of excited charmed (bottom) baryons with large angular momenta, when their masses are close to the DN and D*N (BbarN and Bbar*N) thresholds.

hep-ph↗

arXiv2012

Decays and productions via bottomonium for Z_b resonances and other B anti-B molecules

We discuss decays and productions for the possible molecular states formed by bottom mesons B (B*) and anti-B (anti-B*). The twin resonances found by Belle, Zb(10610) and Zb(10650), are such candidates. The spin wave functions of the molecular states are rearranged into those of heavy and light spin degrees of freedom by using the re-coupling formulae of angular momentum. By applying the heavy quark symmetry we derive model independent relations among various decay and production rates, which can be tested in experiments.

hep-ph↗

arXiv2012

Exotic baryons from a heavy meson and a nucleon

We evaluate a hadronic molecule formed by a heavy meson and a nucleon respecting heavy quark symmetry. The tensor force of pion exchange potential plays a dominate role to produce an strong attraction in this system. Solving coupled channel Schrödinger equations for PN and P* N, we find many bound and resonant states with isospin I=0 while there are few resonances in I=1 state. The rich structures with I=0 indicate that the spectrum of heavy baryons near the threshold is influenced by the contributions from such hadron composite structures.

hep-ph↗

arXiv2012

Exotic mesons with hidden bottom near thresholds

We study heavy hadron spectroscopy near open bottom thresholds. We employ B and B* mesons as effective degrees of freedom near the thresholds, and consider meson exchange potentials between them. All possible composite states which can be constructed from the B and B* mesons are studied up to the total angular momentum J = 0, 1, 2. We consider, as exotic states, isosinglet states with exotic (J,PC) quantum numbers and isotriplet states. We solve numerically the Schrodinger equation with channel-couplings for each state. The masses of twin resonances Zb(10608) and Zb(10653) recently found by Belle are reproduced. We predict several possible bound and/or resonant states in other channels for future experiments.

hep-ph↗