The hyperon--nucleon interaction is investigated through the final-state interaction in the $K^-d\to\pi^-\Lambda p$ reaction.We focus on the $\Lambda N$--$\Sigma N$ coupled-channel interaction, which produces characteristic structures around the $\Sigma N$ thresholds in the $\Lambda p$ invariant mass spectrum.The spin-triplet $\Sigma N\to\Lambda p$ conversion amplitude is constructed within the $K$-matrix formalism using scattering lengths in the isospin basis.We first examine the dependence of the conversion amplitude on the $\Sigma N$ scattering lengths and find that the threshold structure is particularly sensitive to the sign of the real part of the $I=1/2$ scattering length.We then calculate the $\Lambda p$ invariant mass spectrum of the $K^-d\to\pi^-\Lambda p$ reaction, including the contributions from the background diagrams.The resulting spectra show characteristic structures around the $\Sigma N$ thresholds, whose shapes depend on the choice of the interaction parameters. These results suggest that the $\Lambda p$ invariant mass spectrum can serve as a useful observable for constraining the $\Lambda N$--$\Sigma N$ coupled-channel interaction.

We examine the behaviors of masses and decay constants of the three pions depending on the density and the neutron-to-proton density of the isospin-asymmetric nuclear matter. To take into account in-medium effects properly, we use the in-medium chiral perturbation theory. Using the in-medium pion properties, we can also estimate the partial restoration of the chiral symmetry in nuclear matter explicitly by using the in-medium Gell-Mann-Oakes-Renner relation.

Antiprotonic atoms have served as a pivotal tool for investigating the properties of baryon-baryon interactions, including their spin dependence. Examining the spin-orbit splittings induced by their strong interactions also could help clarify the nature of the $\bar{p}$-nucleus interactions and their fraction mediated by scalar and vector mesons. Although the strong spin-orbit splittings for a certain nucleus have been observed experimentally, thorough theoretical investigations have not yet been conducted. In this study, theoretical calculations based on the Dirac equation are systematically performed for nuclei along several isotone "chains." As a result, it is found that the magnitude of the strong spin-orbit splittings exhibits a significant dependence not only on the corresponding level shifts and widths almost linearly, but also on whether the optical potential enters as a vector or scalar potential. These results are expected to provide deeper insights into $\bar{p}$-nucleus interactions, and by extension baryon-baryon interactions, as well as into the properties of the mesons that mediate them.

The hyperon-nucleon interaction is investigated through the final-state interaction in the K^-d^-Λp reaction. We focus on the ΛN-ΣN coupled-channel interaction, which produces characteristic structures around the ΣN thresholds in the Λp invariant mass spectrum. The spin-triplet ΣN conversion amplitude is constructed within the K-matrix formalism using scattering lengths in the isospin basis. We first examine the dependence of the conversion amplitude on the ΣN scattering lengths and find that the threshold structure is particularly sensitive to the sign of the real part of the I=1/2 scattering length. We then calculate the Λp invariant mass spectrum of the K^-d^-Λp reaction, including the contributions from the background diagrams. The resulting spectra show characteristic structures around the ΣN thresholds, whose shapes depend on the choice of the interaction parameters. These results suggest that the Λp invariant mass spectrum can serve as a useful observable for constraining the ΛN-ΣN coupled-channel interaction.

We explain the different spectra for the chiral partner of the vector and the axial vector mesons. The vector meson nonet shows a spectrum consistent with the constituent quark counting. While the axial vector shows the degeneracy like structure for a1(1260), f1(1285), and K1(1270). Also f1(1420) splits from others. The vector mesons and the axial vector mesons are the chiral partners. Simply thinking, the chiral partners should exhibit similar spectrum. To explain those spectra with maintaining the chiral partner property, we introduce a spectrum of axial vector meson nonet with a combination of two effects; singlet-octet splitting and another source of SU(3) breaking. To test them, we construct a model making use of linear sigma model. As a result, we obtain a posssible parameter set. It shows the resolution of degneracy if ⟨σ⟩ becomes smaller.

In this study, we analyze the semileptonic decays of hadrons using Heavy Quark Effective Theory (HQET) to verify the proposed dynamical supersymmetry between the anti-s quark and the ud diquark. Utilizing Heavy Quark Symmetry (HQS) in the heavy quark limit (mQ → ∞), we assume that the Isgur-Wise functions describing the decay transitions of mesons and baryons are identical (ξ(w)=ζ(w)). As a result, we confirm that the decay rate sum rule, which was derived from the equivalence of the wave functions in the previous study, is completely reproduced at the leading order. This clarifies that, in the verification through the decay rate sum rule, the assumption of the equivalence of the Isgur-Wise functions is equivalent to that of the wave functions.

We investigate a type of dynamical chiral symmetry breaking (DχSB) for various current quark masses using the interacting instanton liquid model. The type of DχSB is classified based on the sign of the second derivative of the free energy density with respect to the quark condensate at the origin. We perform numerical simulations of the interacting instanton liquid model with the flavor SU(2) symmetric and (2+1)-flavor quarks. We find that the curvature is negative in the SU(2) case. This means the ordinary type of DχSB. In contrast, in the (2+1)-flavor case, a positive curvature is observed when the strange quark mass is as small as those of the up and down quarks. This suggests that the anomaly-driven type of DχSB can occur under the approximate flavor SU(3) symmetry. As the strange quark mass increases, the curvature gradually decreases and becomes negative when the strange quark mass is approximately three times larger than those of the light quarks. This difference can be understood in terms of the 't Hooft vertex which induces a six-quark interaction in the N_f=3 case and does a four-quark interaction in the N_f=2 case. Our results might indicate that the ratio between the strange and light quark masses plays a crucial role in understanding the microscopic relationship between DχSB and the anomaly effect.

We compute the density dependence of in-medium pion properties, such as mass, wave function renormalization, and decay constant in the correlation function approach, and how they change under the influence of isospin-asymmetric nuclear matter. To this end, we use in-medium chiral perturbation theory to compute the relevant Feynman diagrams up to two-loop diagrams. Our results show that the isospin asymmetry of the nuclear matter splits these quantities into three separate values, corresponding to the three pions. Consequently, the tendency of each in-medium pion mass, wave function renormalization, and decay constant is dependent on the density and the neutron-to-proton ratio rho n/rho p of nuclear matter. We also derive an in-medium Gell-Mann- Oakes-Renner relation which is valid for isospin-asymmetric nuclear matter and investigate to what extent it holds within our calculations.

The K^-d→πΛ N reaction is useful for exploring the hyperon-nucleon interaction through final state interactions. In particular, the cusp structure of the Λ N invariant mass spectrum at the Σ N threshold contains information about the s-wave interaction of 1/2-isospin hyperon-nucleon systems. The calculation of the spectrum is performed with the aim of extracting the scattering length of the Σ N(I=1/2) channel that couples to the Λ N channel from this reaction, and the results are discussed in comparison with experimental data to highlight the factors that should be considered.

This work studies (p) over bar -Ca atom spectra in light of the strong shifts and level widths, using the optical model with several types of parametric coefficients. The spectroscopic quantities are obtained as the eigenvalues of the Dirac equation, where the nuclear densities computed via nuclear density functional theory and the effect of the anomalous magnetic moment are incorporated. The results indicate that the systematical difference of strong shifts between Ca-40 and Ca-48 can never be elucidated by only the conventionally adopted isoscalar b(0) term, necessitating additional contributions from the isovector b(1) and p-wave c(0) terms. Furthermore, it is found that both the strong shifts and the level widths exhibit significant dependence on the nuclear density profiles. These findings demonstrate that the detailed nuclear structures make a significant contribution to the observed spectrum, at least for the calcium isotopes.

The Lambda N invariant mass spectra for the reactions K-d-pi-Lambda p and K-d-pi 0 Lambda n are calculated for experimental study of isospin symmetry breaking in the Lambda N scattering at low energies, the difference in the scattering lengths and effective ranges of Lambda p and Lambda n systems. The calculations are performed for in-flight kaons with a momentum of 1000 MeV/c with employing partial wave analysis up to the p wave for meson-baryon amplitudes and the spin-flip term for baryon-baryon amplitudes. Kinematic selection is utilized to suppress the background processes by selecting forward-emitting pions and higher momentum nucleons. It is worth noting that isospin symmetry breaking in the Lambda N system can be extracted from the difference of the Lambda N invariant mass spectra between the K-d-pi-Lambda p and K-d-pi 0 Lambda n reactions.

Based on simulations of the interacting instanton liquid model (IILM) with three flavor quarks, we compute the free energy density of the QCD vacuum as a function of the quark condensate. We evaluate the second derivative of the free energy density with respect to the quark condensate at the origin. This evaluation makes us to examine whether chiral symmetry breaking in the IILM occurs in an anomaly-driven way. Such a breaking pattern of chiral symmetry has been proposed by a previous study to connect the QCD vacuum structure with the meson propoerties, such as the sigma meson mass. We also perform the quenched simulations, in which no dynamical quarks interact with instantons. This simulation helps us to understand the pattern of chiral symmetry brekaing in the IILM by comparing the full calculation results. We find that in the full IILM chiral symmetry is broken in anomaly-driven way, while for the quenched IILM chiral symmetry is broken in ordinary manner. From these results, we expect that chiral symmetry can be broken in anomaly-driven way even in the real QCD and in phenomena where chiral symmetry breaking plays a crucial role the anomaly effect may also play an important role.

The $K^-d\rightarrow\pi\Lambda N$ reaction is useful for exploring the hyperon-nucleon interaction through final state interactions. In particular, the cusp structure of the $\Lambda N$ invariant mass spectrum at the $\Sigma N$ threshold contains information about the s-wave interaction of 1/2-isospin hyperon-nucleon systems. The calculation of the spectrum is performed with the aim of extracting the scattering length of the $\Sigma N(I=1/2)$ channel that couples to the $\Lambda N$ channel from this reaction, and the results are discussed in comparison with experimental data to highlight the factors that should be considered.

The chiral ward identity connects the in-medium quark condensate to the soft limit value of a correlation function of the pseudoscalar fields evaluated in nuclear medium. For the strange quark condensate, one considers the correlation function of the pseudoscalar fields with strangeness. The correlation function describes in-medium propagation of kaons and it is obtained phenomenologically by kaon-nucleon scattering in the low density approximation. We describe the kaon-nucleon scattering amplitude in chiral perturbation theory and its low energy constants are determined by existent $K^{+}N$ scattering data. Performing analytic continuation of the scattering amplitude obtained by chiral perturbation theory, we can take the soft limit of the scattering amplitude. With this amplitude, we evaluate the in-medium strange quark condensate based on hadron phenomenology.

We compute the vacuum energy density as a function of the quark condensate in the interacting instanton liquid model (IILM) and examine the pattern of dynamical chiral symmetry breaking from its behavior around the origin. This evaluation is performed by using simulation results of the IILM. We find that chiral symmetry is broken in the U(1)_A anomaly assisted way in the IILM with three-flavor dynamical quarks. We call such a symmetry breaking the anomaly-driven breaking which is one of the scenarios of chiral symmetry breaking proposed in the context of the chiral effective theories. We also find that the instanton-quark interaction included in the IILM plays a crucial role for the anomaly-driven breaking by comparing the full and the quenched IILM calculations.

We study the theoretical structure of compositeness with explicit energy dependence, and find a possible explanation for the difficulty in the interpretation of compositeness of deuteron. Compositeness of deuteron is calculated as larger than one in many methods like weak-binding limit. Even though it is widely assumed that the energy dependence in interaction always comes from other states, which we call surjective interpretation, we find that the outcome of deuteron may suggest a violation of surjective interpretation. We directly perform numerical and perturbative calculations of deuteron compositeness. It is concluded that if the energy dependent part of interaction contributes to attraction, compositeness is likely to be enhanced from unity. We discuss the indications of this outcome and the model dependence of compositeness. We propose a straightforward extension and a thorough revise on the formalism of compositeness with field theory considerations.

The possibility of the existence of multiquark hadrons made of 4-quark for mesons and 5-quark for baryons was predicted by Gell-Mann in Ref. [1]. The renewed interest for the search of exotic pentaquark states was initiated by the paper by Diakonov, Petrov, and Polyakov in Ref. [2]. The 2003 experimental reports on the observation of {\Theta^+} pentaquark with a uudd{\bar s} quark content created a big excitement and many following experiments have reported its observation [3]. After high-statistics experiments at JLab, which did not confirm previous claims by the CLAS collaboration, the community concluded that the {\Theta^+} pentaquark either does not exist at all or has an extremely small cross section, making it currently unobserved. There were different review papers on this subject, either questioning the existence of the {\Theta^+} or attempting to explain the reasons why reaching a conclusion based on production experiments is challenging [4]. To address the challenge of minimal 3-body final states, a formation experiment with a projectile kaon beam is proposed. Below, we discuss how the {\Theta^+} could be observed in the KLp \to {\Theta^+} \to {K^+}n reaction in the KLF experiment at JLab [5].

We revisit the low-energy K+N elastic scatterings in the context of the in-medium quark condensate with strange quarks. The chiral ward identity connects the in-medium quark condensate to the soft limit value of the pseudoscalar correlation function evaluated in nuclear matter. The in-medium correlation function of the pseudoscalar fields with strangeness describes in-medium kaon propagation and is obtained by kaon-nucleon scattering amplitudes in the low-density approximation. We construct the kaon-nucleon scattering amplitudes in chiral perturbation theory up to the next-to-leading order and add some terms of the next-to-next-to-leading order with the strange quark mass to improve expansion of the strange quark sector. We also consider the effect of a possible broad resonance state around P-lab = 600 MeV/c for I = 0 reported in the previous study. The low-energy constants are determined by existing K+N scattering data. We obtain good reproduction of the K(+)p scattering amplitude by chiral perturbation theory, while the description of the KN amplitude with I = 0 is not so satisfactory due to the lack of low-energy data. Performing analytic continuation of the scattering amplitudes obtained by chiral perturbation theory to the soft limit, we estimate the in-medium strange quark condensate.

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.