arXiv subjects

Makoto Oka

Publications and source records attributed to Makoto Oka.

At least 19 recordsLinked to original sources

arXiv2026

Alpha-Core Breakup in the Strong Decay of ${}_{ΛΛ}^{6}\mathrm{He}$ to a Deeply Bound $H$ Dibaryon

We investigate the effect of $α$-core breakup on the strong conversion of ${}^{6}_{ΛΛ}\mathrm{He}$ into a deeply bound $H$ dibaryon. In addition to the coherent $H+{}^{4}\mathrm{He}$ channel, we evaluate the open final states $H+p+{}^{3}\mathrm{H}$, $H+n+{}^{3}\mathrm{He}$, and $H+d+d$ using a translationally invariant Gaussian cluster description, including spin-isospin recoupling and full nonrelativistic three-body phase-space integrations. The breakup widths are normalized to Gal's intact-$α$ result. At $B_{ΛΛ}^{H}=176~\mathrm{MeV}$, corresponding to $m_H\simeq2055~\mathrm{MeV}$, the summed breakup width exceeds the intact-$α$ width by a factor $R_{\mathrm{br}}=2.49\times10^{3}$. The resulting inclusive width and lifetime are $Γ_{\mathrm{inc}}=3.87\times10^{-4}~\mathrm{eV}$ and $τ_{\mathrm{inc}}=1.70\times10^{-12}~\mathrm{s}$, respectively, compared with $τ_α=4.25\times10^{-9}~\mathrm{s}$ for the intact-$α$ channel alone. The mass-dependent calculation shows that the inclusive lifetime crosses the characteristic hypernuclear weak-decay timescale near $m_H\simeq2020~\mathrm{MeV}$ and increases rapidly as the $H$ mass decreases. In the representative dark-matter-motivated interval $1865\leq m_H\leq1885~\mathrm{MeV}$, we obtain $6.59\times10^{-4}\lesssimτ_{\mathrm{inc}}\lesssim 6.80\times10^{-3}~\mathrm{s}$, far exceeding the weak-decay timescale. Thus, although core breakup can dominate the inclusive strong width near $m_H\simeq2055~\mathrm{MeV}$, weakly decaying double-$Λ$ hypernuclei remain compatible, within the present framework, with a deeply bound $uuddss$ state in the mass range relevant to sexaquark dark matter.

nucl-th↗

arXiv2026

A Paradigm for the Coupled-Channel Origin of Resonances: the Exotic $T_{c\bar{s}}$ in $D_{s1}(2460/2536)\to D_sππ$

The $T_{c\bar{s}}$ state observed in the decay $D_{s1}(2460)^+ \to D_s^+π^+π^-$ provides direct evidence for an isovector open-charm tetraquark state with strangeness--a discovery that demands a systematic framework connecting its origin to the nature of the parent $D_{s1}$. We successfully achieve this connection by two mechanisms, triangle loops and the coupled channel of $DK$-$D_sπ$ with pure off-diagonal potentials. We first point out the behavior of propagator of $D_sπ$ will influence the effective potential of $DK\to DK$, then we can successfully obtain the pole of $T_{c\bar{s}}$ on the second Reimann Sheet. By combing with the $ππ$-$KK$ rescattering, not only the two-peak structure in $D_{s1}(2460)$ decay is well reproduced, but also a single-peak structure is predicted in $D_{s1}(2536)$ decay. The marked difference, testable at LHCb and Belle II, is driven by the $S$-wave versus $D$-wave nature of their $D^*K$ couplings, revealing the underlying structural distinction between the two $D_{s1}$ states. By directly linking hadronic structure to decay patterns, this work provides a template for deciphering the nature of such exotic states. More broadly, by revealing how non-perturbative coupled-channel effects manifest in exotic hadrons, our analysis connects to a universal mechanism shared by systems ranging from halo nuclei to atomic Feshbach resonances, offering a unified perspective across these fields.

hep-ph↗

arXiv2026

Mass radius and D-term of atomic nuclei in relativistic mean field theory

Based on relativistic mean field theory for atomic nuclei, we compute the mass radius and other radii associated with the energy momentum tensor for dozens of spin-0 nuclei across the nuclear chart. We also compute the D-term of these nuclei, the forward limit of the gravitational form factor $D(t=0)=D$. The dependence on the neutron number $N$ is systematically studied for calcium (Ca), nickel (Ni), zirconium (Zr), tin (Sn) and lead (Pb) isotopes. Remarkably, $|D|$ does not monotonically increase with $N$. Instead, it exhibits local maxima and minima when $N$ equals a magic number and even a sub-magic number. This results in characteristic kinks in the mass, scalar, tensor and shear radii of these isotopes. Our work for the first time elucidates the strong sensitivity of the various mechanical properties of nuclei to the nuclear shell structure.

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arXiv2025

Quark-model search for compact $c\bar c uds$ pentaquark states

A potential quark model is used to search for a $P_{c\bar{c}s}^0=(c\bar{c}uds)^0$, $J^P=1/2^-$ pentaquark state that has recently been observed experimentally by the LHCb collaboration at 4338.2 MeV, with a width of 7.0 MeV and high statistical significance $>15σ$. Our model Hamiltonian reproduces the masses of the low-lying charmed and strange hadrons. We use the Gaussian expansion method {to solve the} five-body Schrödinger equation. Employing the real scaling method {including} the relevant meson-baryon thresholds explicitly, sharp resonances are distinguished from the meson-baryon scattering states. We incorporate new color states of the color-octet meson and baryon configurations as well as the color-singlet configurations for the five-quark states. We find no $ J^P=1/2^-$ resonance close to the observed state, and also none in the $ J^P=3/2^-$ state. This increases the likelihood that $P^0_{c\bar{c}s}$ is a $Ξ_c\bar{D}$ hadronic molecule rather than a compact state.

hep-ph↗

arXiv2025

Resonance sum rules: an application to the square well potential

We propose an extension of the Quantum Chromodynamics (QCD) sum rules, termed the Resonance sum rules (RSR), to access resonance poles in the complex energy plane. By strategically introducing a contour in the complex plane and conformal mapping, the method intends to reach resonance poles on the second Riemann sheet. To validate this approach, we apply RSR to the square-well potential model, for which the pole locations are known. The analysis demonstrates a successful extraction of the pole positions and residues for both the $S$-wave and $P$-wave resonances. The results are in good agreement with the analytic solutions, with discrepancies within $5\%$ for the pole positions and $20\%$ for the residues.This framework provides a basis for future applications to realistic hadronic resonances, promising new insights into spectral properties of QCD.

hep-ph↗

arXiv2025

Strange pentaquarks with a hidden heavy quark-antiquark pair

The strange pentaquarks with hidden heavy quark pair ($q^3c\bar c$ and $q^3b \bar b$) are investigated by the coupled-channel quark cluster model. Two types of the $q^3$ color-octet configurations are found to provide the attraction, which makes bound states, sharp resonances, and cusps in the baryon meson scattering. A resonance appears at around 4500 MeV in the strange hidden charm sector. Such structures are more clearly seen in the hidden bottom systems.

hep-ph↗

arXiv2025

Fate of $Σ_c$, $Ξ_c'$ and $Ω_c$ baryons at high temperature with chiral restoration

Masses of the singly heavy baryons (SHBs), composed of a heavy quark and a light diquark, are studied from the viewpoints of heavy-quark spin symmetry (HQSS) and chiral-symmetry restoration at finite temperature. We consider the light diquarks with spin-parity $J^P=0^\pm$ and $1^\pm$. Medium corrections to the SHBs are provided through the diquarks whereas the heavy quark is simply regarded as a spectator. The chiral dynamics of the diquark are described by the Nambu-Jona-Lasinio (NJL) model having (pseudo)scalar-type and (axial)vector-type four-point interactions and the six-point ones responsible for the $U(1)_A$ axial anomaly. The divergences are handled by means of the three-dimensional proper-time regularization with both ultraviolet and infrared cutoffs included, in order to eliminate unphysical imaginary parts. As a result, the mass degeneracies between the parity partners of all the SHBs are predicted in accordance with the chiral restoration. In particular, the HQS-doublet SHBs exhibit clear mass degeneracies due to the absence of the direct anomaly effects. We also predict a mass degeneracy of $Σ_c$ and $Ω_c$ above the pseudocritical temperature $T_{\rm pc}$ of chiral restoration, which results in a peculiar mass hierarchy for positive-parity HQS-doublet SHBs where $Ξ_c'$ becomes heavier than $Ω_c$ Besides, it is found that the decay width of $Σ_c\toΛ_cπ$ vanishes above $T_{\rm pc}$ reflecting a closing of the threshold. The predicted modifications of masses and decay widths of the SHBs are expected to provide future heavy-ion collision experiments and lattice simulations with useful information on chiral dynamics of the diquarks.

hep-ph↗

arXiv2025

Chiral effective theory of scalar and vector diquarks revisited

Chiral effective theory of light diquarks is revisited. We construct an effective Lagrangian based on the linear representation of three-flavor chiral symmetry. Here, we focus on the effect of a chiral and $U(1)_A$ symmetric term originated from an eight-point quark interaction. From this model, we obtain the mass formulas of scalar, pseudoscalar, vector, and axial-vector diquarks, which also describe the dependence of diquark masses on the spontaneous chiral symmetry breaking and the $U(1)_A$ anomaly. We regard singly heavy baryons as two-body systems composed of one heavy quark and one diquark and then predict the fate of the mass spectrum and the strong decay widths under chiral symmetry restoration.

hep-ph↗

arXiv2024

New insight into the exotic states strongly coupled with the $D\bar{D}^*$ from the $T^+_{cc}$

We have investigated the internal structure of the open- and hidden-charmed ($DD^*$/$\bar DD^*$) molecules in the unified framework. We first fit the experimental lineshape of the $T^+_{cc}$ state and extract the $DD^*$ interaction, from which the $T^+_{cc}$ is assumed to arise solely. Then we obtain the $D\bar{D}^*$ interaction by charge conjugation. Our results show that the $D\bar{D}^*$ interaction is attractive but insufficient to form $X(3872)$ as a bound state. Instead, its formation requires the crucial involvement of the coupled channel effect between the $D\bar D^*$ and $c\bar c$ components, although the $c\bar c$ accounts for approximately $1\%$ only. Besides $X(3872)$, we have obtained a higher-energy state around $3957.9$ MeV with a width of $16.7$ MeV, which may be a potential candidate for the $X(3940)$. In $J^{PC}=1^{+-}$ sector, we have found two states related to the iso-scalar $\tilde X(3872)$ and $h_c(2P)$, respectively. Our combined study provides valuable insights into the nature of these $DD^*$/$D\bar D^*$ exotic states.

hep-ph↗

arXiv2024

Structure of Heavy Mesons in the Light-Front Quark Model

We investigate the structure of ground-state heavy mesons within the light-front quark model, utilizing wave functions derived from the Single Gaussian Ansatz (SGA) and the Gaussian Expansion Method (GEM). By performing a $χ^2$ fit to static properties such as mass spectra and decay constants, we determine the model parameters for each approach. We then compare the impacts of both methods on the light-front wave functions and structural observables. Our analysis reveals significant differences in the distribution amplitudes (DAs) $ϕ_{2;M}(x)$ near the endpoints, with GEM showing enhanced amplitudes and correct asymptotic behavior $ϕ_{2;M}(x \to 1) \propto (1-x)$, consistent with perturbative QCD. This endpoint behavior is linked to the short-range (high-momentum) wave function governed by color Coulomb interaction and relativistic kinematics. GEM accurately reproduces a power-law damping $ψ_0(k \to \infty) \propto 1/k_\perp^2$, aligning with perturbative QCD predictions. Furthermore, the electromagnetic form factors of pseudoscalar mesons in the low-$Q^2$ region fall off faster with GEM than with SGA. Overall, while both methods adequately describe static properties, GEM provides a more accurate description of structural properties, being more sensitive to details and asymptotic behaviors.

hep-ph↗

arXiv2024

Mass Spectra of Full-Heavy and Double-Heavy Tetraquark States in the Conventional Quark Model

A comprehensive study of the $S$-wave heavy tetraquark states with identical quarks and antiquarks, specifically $QQ{\bar Q'}\bar Q'$ ($Q, Q'=c,b$), $QQ\bar s\bar s$/$\bar Q\bar Q ss$, and $QQ\bar q\bar q$/$\bar Q\bar Q qq$ ($q=u,d$), are studied in a unified constituent quark model. This model contains the one-gluon exchange and confinement potentials. The latter is modeled as the sum of all two-body linear potentials. We employ the Gaussian expansion method to solve the full four-body Schrödinger equations, and search bound and resonant states using the complex-scaling method. We then identify $3$ bound and $62$ resonant states. The bound states are all $QQ\bar q\bar q$ states with the isospin and spin-parity quantum numbers $I(J^P)=0(1^+)$: two bound $bb\bar{q}\bar{q}$ states with the binding energies, 153 MeV and 4 MeV below the $BB^*$ threshold, and a shallow $cc\bar{q}\bar{q}$ state at $-15$ MeV from the $DD^*$ threshold. The deeper $bb\bar q \bar q$ bound state aligns with the lattice QCD predictions, while $cc\bar q\bar q$ bound state, still has a much larger binding energy than the recently observed $T^+_{cc}$ by LHCb collaboration. No bound states are identified for the $QQ\bar Q'\bar Q'$, $QQ\bar s\bar s$ and $QQ\bar q\bar q$ with $I=1$. Our analysis shows that the bound $QQ\bar Q'\bar Q'$ states are more probable with a larger mass ratio, $m_Q/m_{Q'}$. Experimental investigation for these states is desired, which will enrich our understanding of hadron spectroscopy and probe insights into the confinement mechanisms within tetraquarks.

hep-ph↗

arXiv2023

Doubly heavy tetraquarks including one-pion exchange potential

Spectrum of the doubly heavy tetraquarks is studied in a constituent quark model including one-pion exchange (OPE) potential. Central and tensor forces induced by OPE between two light quarks are considered. Our results show that $I(J^P)=0(1^+)$ compact bound states are shifted up because of the repulsive central force between $\bar{q}\bar{q}$. This effect possibly leads to the small binding energy in $T_{cc}$. In addition, a $I(J^P)=1(1^+)$ resonant state is reported with $ E=10641 \ \rm{MeV},Γ=15 \ \rm{MeV}$ and $ E=10640 \ \rm{MeV},Γ=15 \ \rm{MeV}$, without and with including OPE potential, respectively. The repulsive central force and attractive tensor force almost cancel with each other and leave a small energy difference when OPE potential is included.

nucl-th↗

arXiv2023

Axial anomaly effect on three-quark and five-quark singly heavy baryons

Effects of the $U(1)_A$ axial anomaly on the mass spectrum of singly heavy baryons (SHBs) is studied in terms of the chiral effective theory based on the chiral linear representation for light flavors. We consider SHBs made of both three quarks ($Qqq$) and five quarks ($Qqqq\bar{q}$). For the three-quark SHBs we prove that the inverse mass hierarchy for the negative-parity $Λ_c$ and $Ξ_c$ is realized only when the $U(1)_A$ anomaly is present. For the five-quark SHBs, in contrast, it is found that the $U(1)_A$ anomaly does not change the mass spectrum at the leading order, and accordingly their decay properties induced by emitting a pseudoscalar meson are not affected by the anomaly. Moreover, taking into account small mixings between the three-quark and five-quark SHBs, we find that the observed $Ξ_c$ excited state, either $Ξ_c(2923)$ or $Ξ_c(2930)$, can be consistently regarded as a negative-parity SHB that is dominated by the five-quark component. We also predict a new negative-parity five-quark dominant $Λ_c$, whose mass is around $2700$ MeV and the decay width is of order a few MeV, which provides useful information for future experiments to check our description.

hep-ph↗

arXiv2023

Quark Confinement for Multi-Quark Systems -- Application to Fully-Charmed Tetraquarks

A new color basis system and confinement mechanism for multi-quark systems are proposed according to the string-type picture of QCD. The color string configurations in the strong coupling QCD are implemented in the set of color basis states. The extended color Hilbert space for $QQ\bar Q\bar Q$ systems includes a ''hidden color'' state, which mixes with two-meson states $Q\bar Q+Q\bar Q$, This mixing effect leads to an attractive potential sufficient to form a bound state. We apply a realistic Hamiltonian model with the new scheme to fully charmed tetraquark states, $cc\bar c\bar c$, and find a bound and two resonant states, which could potentially correspond to the $cc\bar c\bar c$ tetraquark candidates recently observed in experiments.

hep-ph↗

arXiv2023

Axial anomaly effect to the chiral-partner structure of diquarks at high temperature

Masses of positive-parity and negative-parity diquarks are investigated at finite temperature with a quark chemical potential. We employ the three-flavor Nambu-Jona-Lasinio model, in order to delineate chiral properties of the diquarks, in particular, the mass degeneracy of chiral partners under extreme conditions. We focus on the effects of $U(1)_A$ axial anomaly on manifestation of the chiral-partner structures. We find that, in the absence of anomaly effects to the diquarks, the mass degeneracies in all $[ud]$, $[su]$ and $[sd]$ diquark sectors take place prominently above the pseudocritical temperature of the chiral restoration. On the other hand, the anomaly effects are found to hinder the $[ud]$ diquark from exhibiting the mass degeneracy, accompanied by a slow reduction of the $\bar{s}s$ condensate, while the $[su]$ and $[sd]$ diquarks are not much affected. Our present investigation will provide useful information on the chiral-partner structure with the anomaly effects of diquarks for heavy-ion collision experiments of singly heavy baryons and doubly heavy tetraquarks, and for future lattice simulations of the diquarks.

hep-ph↗

arXiv2023

Strong decays of singly heavy baryons from a chiral effective theory of diquarks

A chiral effective theory of scalar and vector diquarks is formulated, which is based on $SU(3)_R\times SU(3)_L$ chiral symmetry and includes interactions between scalar and vector diquarks with one or two mesons. We find that the diquark interaction term with two mesons breaks the $U(1)_A$ and flavor $SU(3)$ symmetries. To determine the coupling constants of the interaction Lagrangians, we investigate one-pion emission decays of singly heavy baryons $Qqq$ ($Q=c, b$ and $q=u,d,s$), where baryons are regarded as diquark--heavy-quark two-body systems. Using this model, we present predictions of the unobserved decay widths of singly heavy baryons. We also study the change of masses and strong decay widths of singly heavy baryons under partial restoration of chiral symmetry.

hep-ph↗

arXiv2023

Spin-Flavor SU(6) Symmetry for Baryon-Baryon Interactions

Short-range parts of the baryon-baryon ($BB$) interactions are analyzed from the spin-flavor $SU(6)_{sf}\supset SU(3)_f \times SU(2)_s$ symmetry viewpoint. Due to the Pauli principle of quarks, the symmetry structure of the wave functions is restricted at short distances. Consequently, the $BB$ states with the same spin-flavor quantum numbers may be reduced into one or a few spin-flavor states. Such reduction causes repulsion and/or suppression of transitions at short distances. We show that the observed suppression of the $ΞN \to ΛΛ$ conversion can be explained following the above argument. It is also applied to the suppression of the $ΣN$ to $ΛN$ conversion in the spin 1 and isospin 1/2 channel. Furthermore, the effects of the color-magnetic interaction (CMI), which prefers flavor antisymmetric states, to the Pauli-allowed states are discussed.

nucl-th↗

arXiv2022

The investigations of the $P$-wave $B_s$ states combining quark model and lattice QCD in the coupled channel framework

Combining the quark model, the quark-pair-creation mechanism and $B^{(*)}\bar K$ interaction, we have investigated the near-threshold $P$-wave $B_s$ states in the framework of the Hamiltonian effective field theory. With the heavy quark flavor symmetry, all the parameters are determined in the $D_s$ sector by fitting the lattice data. The masses of the bottom-strange partners of the $D^{*}_{s0}(2317)$ and $D^{*}_{s1}(2460)$ are predicted to be $M_{B^{*}_{s0}}=5730.2_{-1.5}^{+2.4}$ MeV and $M_{B^{*}_{s1}}= 5769.6_{-1.6}^{+2.4}$ MeV, respectively, which are well consistent with the lattice QCD simulation. The two $P$-wave $B_s$ states are the mixtures of the bare $\bar b s$ core and $B^{(*)}\bar K$ component. Moreover, we find a crossing point between the energy levels with and without the interaction Hamiltonian in the finite volume spectrum in the $0^+$ case, which corresponds to a CDD (Castillejo-Dalitz-Dyson) zero in the $T$-matrix of the $B\bar K$ scattering. This CDD zero will help deepen the insights of the near-threshold states and can be examined by future lattice calculation.

hep-lat↗