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The mini proceedings of the "Fourth International Workshop on the Extension Project for the J-PARC Hadron Experimental Facility (HEF-ex 2024) [https://kds.kek.jp/event/46965]" held at J-PARC, February 19-21, 2024, are presented. The workshop was devoted to discussing the physics case that connects both the present and the future Hadron Experimental Facility at J-PARC, covering a wide range of topics in flavor, hadron, and nuclear physics related to both experimental and theoretical activities being conducted at the facility.

We theoretically investigate kaonic atom states based on the latest high precision data of the $2p$ states of the kaonic atoms in $^3$He and $^4$He (J-PARC E62). We consider the phenomenological form for the optical potential proportional to the nuclear density distributions and determine the potential parameters by the latest data. We find two sets of potential parameters for each of $K^--^3$He and $K^--^4$He that reproduce the data. We then extract the potential parameters consistent with the data of $^3$He and $^4$He atoms simultaneously. Using the potential, we investigate the structure of the kaonic atoms and kaonic nuclei for various nuclei up to Sn. We also report the optical potential parameters suited for the global description of the atomic data, the possible strong isospin dependence of the potential, and the different strength of the data of $K^--^3$He and $K^--^4$He in the restrictions on the potential parameters. In addition, we find that the study of the $1s$ states of the kaonic helium atom is very interesting as a next step, and the determination of the orbital angular momenta of the kaonic nuclear states is helpful for the unified understandings of the atomic and nuclear bound states of kaon because of the mutual influence between the atomic and the nuclear states of kaon with the same orbital angular momentum., Comment: 22 pages, 14 figures

The excitation spectra of \Lambda_c and \Lambda_b baryons are investigated by using a quark-diquark model in which a single-heavy baryon is treated as the bound state of a heavy quark and a scalar diquark. We take two types of relativistic corrections into account for the quark-diquark potential. In the first type, we consider the one-gluon exchange between the heavy quark and one of the light quarks in the diquark. In the second, we consider the one-gluon exchange between a scalar particle and a heavy quark. We find that there is a large difference between two types of corrections due to different treatment of the internal color structure of the diquark. The relativistic corrections are important for the solution to the string tension puzzle, particularly, the Darwin term makes a large contribution., Comment: 15 pages, 9 figures, 2 tables

The $\eta$ mesic nucleus is considered to be one of the interesting exotic many body systems and has been studied since 1980's theoretically and experimentally. Recently, the formation of the $\eta$ mesic nucleus in the fusion reactions of the light nuclei such as $d + d \rightarrow (\eta + \alpha) \rightarrow X$ has been proposed and the experiments have been performed by WASA-at-COSY. We develop a theoretical model to evaluate the formation rate of the $\eta$ mesic nucleus in the fusion reactions and show the calculated results. We find that the $\eta$ bound states could be observed in the reactions in cases with the strong attractive and small absorptive $\eta$-nucleus interactions. We compare our results with existing data of the $d + d \rightarrow \eta + \alpha$ and the $d + d \rightarrow {^3 \rm He} + N + \pi$ reactions. We find that the analyses by our theoretical model with the existing data can provide new information on the $\eta$-nucleus interaction., Comment: 14 pages, 31 figures, 1 table, submitted to EPJA

Excitation-energy spectra of $^{11}$C nuclei near the $\eta^\prime$-meson production threshold have been measured by missing-mass spectroscopy using the $^{12}$C($p$,$d$) reaction. A carbon target has been irradiated with a 2.5 GeV proton beam supplied by the synchrotron SIS-18 at GSI to produce $\eta^\prime$ meson bound states in $^{11}$C nuclei. Deuterons emitted at $0^\circ$ in the reaction have been momentum-analyzed by the fragment separator (FRS) used as a high-resolution spectrometer. No distinct structure due to the formation of $\eta^\prime$-mesic states is observed although a high statistical sensitivity is achieved in the experimental spectra. Upper limits on the formation cross sections of $\eta^\prime$-mesic states are determined, and thereby a constraint imposed on the $\eta^\prime$-nucleus interaction is discussed., Comment: 13 pages, 14 figures, accepted for publication in Physical Review C

Excitation spectra of $^{11}$C were measured in the $^{12}$C$(p,d)$ reaction near the $\eta'$ emission threshold. A proton beam extracted from the synchrotron SIS-18 at GSI with an incident energy of 2.5 GeV impinged on a carbon target. The momenta of deuterons emitted at 0 degrees were precisely measured with the fragment separator FRS operated as a spectrometer. In contrast to theoretical predictions on the possible existence of deeply bound $\eta'$ mesic states in carbon nuclei, no distinct structures were observed associated with the formation of bound states. The spectra were analyzed to set stringent constraints on the formation cross section and on the hitherto barely-known $\eta'$-nucleus interaction., Comment: 6 pages, 4 figures

The possible existence of \eta'-nucleus bound states has been put forward through theoretical and experimental studies. It is strongly related to the \eta' mass at finite density, which is expected to be reduced because of the interplay between the $U_A(1)$ anomaly and partial restoration of chiral symmetry. The investigation of the C(p,d) reaction at GSI and FAIR, as well as an overview of the experimental program at GSI and future plans at FAIR are discussed., Comment: 7 pages, 3 figures; talk at the International Conference on Exotic Atoms and Related Topics (EXA2014), Vienna, Austria, 15-19 September 2014. in Hyperfine Interactions (2015)

The mass of the {\eta}' meson is theoretically expected to be reduced at finite density, which indicates the existence of {\eta}'-nucleus bound states. To investigate these states, we perform missing-mass spectroscopy for the (p, d) reaction near the {\eta}' production threshold. The overview of the experimental situation is given and the current status is discussed., Comment: 6 pages, 3 figures; talk at II Symposium on applied nuclear physics and innovative technologies, September 24th - 27th, 2014, Jagiellonian University, Krak\'ow Poland; to appear in Acta Physica Polonica B

In this talk we present an interpretation for the experimental data available on two different processes, namely, $J/\Psi \to \phi \pi^+ \pi^-$, $J/\Psi\to \gamma \omega \phi$, which seem to indicate existence of two new resonances with the same quantum numbers ($J^{\pi c}=0^{++}, I = 0$) and very similar mass (~1800 MeV) but with very different decay properties. However, our studies show that the peak structure found in the $\omega \phi$ invariant mass, in $J/\Psi \to \gamma \omega \phi$, is a manifestation of the well known $f_0(1710)$ while the cross section enhancement found in $J/\Psi \to \phi \pi^+ \pi^-$ is indeed a new $f_0$ resonance with mass near 1800 MeV. We present an explanation for the different decay properties of these two scalar resonances., Comment: Proceedings for the nuclear physics meeting ("XXXVI Reuni\~ao de trabalho sobre f\'isica nuclear no Brasil") held in Maresias during Sept. 1-5. To be published as AIP proceedings

Recent CLAS data for the pi Sigma invariant mass distributions (line-shapes) in the gamma p -> K^+ pi Sigma reaction are theoretically investigated. The line-shapes have peaks associated with the Lambda(1405) excitation. Our model consists of gauge invariant photo-production mechanisms, and the chiral unitary model that gives the rescattering amplitudes where Lambda(1405) is contained. It is found that, while the pi Sigma line-shape data in the Lambda(1405) region are successfully reproduced by our model for all the charge states, the production mechanism is not so simple that we need to introduce parameters associated with short-range dynamics to fit the data. Our detailed analysis suggests that the nonresonant background contribution is not negligible, and its sizable effect shifts the Lambda(1405) peak position by several MeV. We also analyze the data using a Breit-Wigner amplitudes instead of those from the chiral unitary model. We find that the fitted Breit-Wigner parameters are closer to the higher pole position for Lambda(1405) of the chiral unitary model. This work sets a starting point for a fuller analysis in which line-shape as well as K^+ angular distribution data are simultaneously analyzed for extracting Lambda(1405) pole(s)., Comment: 27 pages, 23 figures; published version, 4 figures added, some discussions added, typos corrected

Recently, many efforts are being put in studying three-hadron systems made of mesons and baryons and interesting results are being found. In this talk, I summarize the main features of the formalism used to study such three hadron systems with strangeness $S=-1,0$ within a framework built on the basis of unitary chiral theories and solution of the Faddeev equations. In particular, I present the results obtained for the $\pi\bar{K}N$, $K\bar{K}N$ and $KK\bar{K}$ systems and their respective coupled channels. In the first case, we find four $\Sigma$'s and two $\Lambda$'s with spin-parity $J^P=1/2^+$, in the 1500-1800 MeV region, as two meson-one baryon s-wave resonances. In the second case, a $1/2^+$ $N^*$ around 1900 MeV is found. For the last one a kaon close to 1420 MeV is formed, which can be identified with K(1460)., Comment: Proceeding written for the HYP2012 conference

We investigate the $\bar KN$ and coupled channels system in a finite volume and study the properties of the $\Lambda(1405)$ resonance. We calculate the energy levels in a finite volume and solve the inverse problem of determining the resonance position in the infinite volume. We devise the best strategy of analysis to obtain the two poles of the $\Lambda(1405)$ in the infinite volume case, with sufficient precision to distinguish them., Comment: Proceeding written for the NSTAR2013 conference

In order to study partial restoration of the chiral symmetry at finite density, we investigate the density corrections of the chiral condensate up to next-leading order of density expansion using the chiral Ward identity and an in-medium chiral perturbation theory. In our study, we assume that all the in-vacuum quantities for the pion, the nucleon and the pi N interaction are determined and focus on density expansion of the in-medium physical quantities. We perform diagrammatic analysis of the correlation functions which provide the in-medium chiral condensate. This density expansion scheme shows that medium effects to the chiral condensate beyond the linear density come from density corrections to the pi N sigma term as a result of the interactions between pion and nucleon in nuclear matter. We also discuss that higher density contributions beyond order of rho^2 cannot be fixed only by the in-vacuum pi N dynamics but we need NN two-body dynamics in vacuum to fix divergence appearing in the calculation of the rho^2 dependence of the chiral condensate with the pi N dynamics., Comment: 13 pages, 9 figures

We discuss the exotic hadron structure and hadron-hadron interactions in view of heavy ion collisions. First, we demonstrate that a hadronic molecule with a large spatial size would be produced more abundantly in the coalescence model compared with the statistical model result. Secondly, we constrain the Lambda-Lambda interaction by using the recently measured Lambda-Lambda correlation data. We find that the RHIC-STAR data favor the Lambda-Lambda scattering parameters in the range 1/a_0 <= -0.8 fm^{-1} and r_{eff} >= 3 fm., Comment: 8 pages, 5 figures. Talk presented at the 11th International Conference on Hypernuclear and Strange Particle Physics (HYP2012), Oct.1-5, 2012, Barcelona, Spain

Effective nuclear densities probed by kaon- and anti-kaon-nucleus systems are studied theoretically both for bound and low energy scattering states. As for the anti-kaon bound states, we investigate kaonic atoms. We find that the effective density depends on the atomic states significantly and we have the possibility to obtain the anti-kaon properties at various nuclear densities by observing the several kaonic atom states. We also find the energy dependence of the probed density by kaon and anti-kaon scattering states. We find that the study of the effective nuclear density will help to find the proper systems to investigate the meson properties at various nuclear densities., Comment: 4 pages, 4 figures, talk given at XI International Conference on Hypernuclear and Strange Particle Physics (HYP2012), Oct. 1-5, 2012, Barcelona, SPAIN

We calculate theoretically the formation spectra of eta'(958)-nucleus systems in the (p,d) reaction for the investigation of the in-medium modification of the eta' mass. We show the comprehensive numerical calculations based on a simple form of the eta' optical potential in nuclei with various potential depths. We conclude that one finds an evidence of possible attractive interaction between eta' and nucleus as peak structure appearing around the eta' threshold in light nuclei such as 11C when the attractive potential is stronger than 100 MeV and the absorption width is of order of 40 MeV or less. Spectroscopy of the (p,d) reaction is expected to be performed experimentally at existing facilities, such as GSI. We also estimate the contributions from the omega and phi mesons, which have masses close to the eta' meson, concluding that the observation of the peak structure of the eta'-mesic nuclei is not disturbed although their contributions may not be small., Comment: 8 pages, 8 figures

The $K^- d \to \pi YN$reaction is theoretically studied so as to investigate the $K^{-}$-induced production of the hyperon resonances $\Sigma (1385)$ and $\Lambda (1405)$. For this purpose we take into account the p-wave amplitudes for the meson-baryon two-body scatterings as well as the s-wave amplitudes. Due to the fact that the hyperon resonances are selectively produced from the $\bar{K} N$ channel in this reaction, the $\Lambda (1405)$ peak appears at 1420 MeV, which implies that $\Lambda (1405)$ and $\Sigma (1385)$ could be separately seen in the missing mass spectrum of the emitted nucleon in the $K^{-} d \to n X$ reaction. The $\pi Y$ invariant mass spectrum in this study is consistent with experimental data both for $\Sigma (1385)$ and $\Lambda (1405)$. The pion exchange contributions are also included and are found to give smooth background without distorting the peak structure of the hyperon resonances., Comment: 20 pages, 12 figures

We review recent work concerning the $\bar{K}N$ interaction and Faddeev equations with chiral dynamics which allow us to look at the $\bar{K}NN$ from a different perspective and pay attention to problems that have been posed in previous studies on the subject. We show results which provide extra experimental evidence on the existence of two $\Lambda(1405)$ states. We then show the findings of a recent approach to Faddeev equations using chiral unitary dynamics, where an explicit cancellation of the two body off shell amplitude with three body forces stemming from the same chiral Lagrangians takes place. This removal of the unphysical off shell part of the amplitudes is most welcome and renders the approach unambiguous, showing that only on shell two body amplitudes need to be used. With this information in mind we use an approximation to the Faddeev equations within the fixed center approximation to study the $\bar{K}NN$ system, providing answers within this approximation to questions that have been brought before and evaluating binding energies and widths of this three body system. As a novelty with respect to recent work on the topic we find a bound state of the system with spin S=1, like a bound state of $\bar{K}$-deuteron, less bound that the one of S=0, where all recent efforts have been devoted. The width is relatively large in this case, suggesting problems in a possible experimental observation., Comment: 18 pages, 7 figures, one misprint corrected, Nuclear Physics A in press

Theoretical studies within the chiral unitary approach, and recent experiments, have provided evidence of the existence of two isoscalar states in the region of the $\Lambda(1405)$. In this paper we use the same chiral approach to generate energy levels in a finite box. In a second step, assuming that these energies correspond to lattice QCD results, we devise the best strategy of analysis to obtain the two states in the infinite volume case, with sufficient precision to distinguish them. We find out that using energy levels obtained with asymmetric boxes and/or with a moving frame, with reasonable errors in the energies, one has a successful scheme to get the two $\Lambda(1405)$ poles., Comment: Published version (more discussions added based on referee's suggestions, giving rise to a new section: IV)

We estimate the valence quark contributions for the gamma* Y -> Lambda* (Y=Lambda, Sigma0) electromagnetic transition form factors. We focus particularly on the case Lambda*=Lambda(1670) as an analog reaction with gamma* N -> N(1535). The results are compared with those obtained from chiral unitary model, where the Lambda* resonance is dynamically generated and thus the electromagnetic structure comes directly from the meson cloud excitation of the baryon ground states. The form factors for the case Y=Sigma0 in particular, depend crucially on the two real phase (sign) combination, a phase between the Lambda and Lambda* states, and the other, the phase between the Lambda and Sigma0 radial wave functions. Depending on the combination of these two phases, the form factors for the gamma* Sigma0 -> Lambda* reaction can be enhanced or suppressed. Therefore, there is a possibility to determine the phase combination by experiments., Comment: 17 pages, 7 figures

We develop a model to evaluate the formation rate of the heavy mesic nuclei in the two nucleon pick-up reactions, and apply it to the $^6$Li target cases for the formation of heavy meson-$\alpha$ bound states, as examples. The existence of the quasi-deuteron in the target nucleus is assumed in this model. It is found that the mesic nuclei formation in the recoilless kinematics is possible even for heavier mesons than nucleon in the two nucleon pick-up reactions. We find the formation rate of the meson-$\alpha$ bound states can be around half of the elementary cross sections at the recoilless kinematics with small distortions., Comment: 1 table, 10 figures, 8 pages

An SU(4) extrapolation of the chiral unitary theory in coupled channels done to study the scalar mesons in the charm sector is extended to produce results in finite volume. The theory in the infinite volume produces dynamically the $D_{s^*0}(2317)$ resonance by means of the coupled channels $KD$, $\eta D_s$. Energy levels in the finite box are evaluated and, assuming that they would correspond to lattice results, the inverse problem of determining the bound states and phase shifts in the infinite volume from the lattice data is addressed. We observe that it is possible to obtain accurate $KD$ phase shifts and the position of the $D_{s^*0}(2317)$ state, but it requires the explicit consideration of the two coupled channels in the analysis if one goes close to the $\eta D_s$ threshold. We also show that the finite volume spectra look rather different in case the $D_{s^*0}(2317)$ is a composite state of the two mesons, or if it corresponds to a non molecular state with a small overlap with the two meson system. We then show that a careful analysis of the finite volume data can shed some light on the nature of the $D_{s^*0}(2317)$ resonance as a $KD$ molecule or otherwise., Comment: Published version

The $K^{-}$ induced production of $\Lambda(1405)$ in the $K^{-} d \to \pi \Sigma n$ reaction is investigated having in mind the conditions of the DAFNE facility at Frascati. We find that the fastest kaons from the decay of the $\phi$ at DAFNE are well suited to see this resonance if one selects forward going neutrons in the center of mass, which reduce the contribution of single scattering and stress the contribution of the double scattering where the signal of the resonance appears clearer. We take advantage to report briefly on a recent work in which in addition to the $\bar{K}NN$ system with total spin S=0, we find a less bound state (although with equally large width) with S=1, like in the $K^{-} d$ reported in the first part., Comment: Contribution to the Hadron 2011 Workshop, Muenchen June 2011

A study of three-pseudoscalar $\pi K \bar{K}$ and $\pi \pi \eta$ coupled system is made by solving the Faddeev equations within an approach based on unitary chiral dynamics. A resonance with total isospin one and spin-parity $J^\pi = 0^-$ is found with mass $\sim$ 1400 MeV when the $K \bar{K}$ system gets reorganized as the $f_0(980)$. This resonance is identified with the $\pi (1300)$ listed by the Particle Data Group. Further, the two-body amplitude which describes the interaction between a $\pi$ and the $f_0(980)$ is extracted from the study of the $\pi K\bar K$ and $\pi\pi\eta$ system and is then employed to study the $f_0(980)\pi \pi $ system. As a result, a scalar resonance is found near 1790 MeV which drives the two $ f_0 (980)\pi$ systems to resonate as the $\pi (1300)$ while the invariant mass of the two pions falls in the mass region of the scalar $\sigma (600)$. These findings support the existence of a new $f_0$ resonance near 1790 MeV, as found by the BES and Crystal Barrel collaborations. Our results show that this $f_0(1790)$ is definitely distinct to $f_0(1710)$, the latter of which seems to possess a glueball structure dominantly.

The $K K\bar K$ system is investigated with a coupled channel approach based on solving the Faddeev equations considering the $KK\bar K$, $K\pi\pi$ and $K\pi\eta$ channels and using as input two-body $t$-matrices that generate dynamically the $f_0(980)$ and $a_0(980)$ resonances. In the present calculation, a quasibound state around 1420 MeV with total isospin $I=1/2$ and spin-parity $J^\pi=0^-$ is found below the three kaon threshold. This state can be identified with the K(1460) resonance listed by the Particle Data Group. We also study the $KK\bar K$ system in a single channel three-body potential model with two-body effective $KK$ and $K\bar K$ interactions, in which the $K\bar K$ interaction is adjusted to reproduce the properties of the $f_0(980)$ and $a_0(980)$ resonances as $K\bar K$ bound states, obtaining a very similar result to the one found in the Faddeev approach., Comment: Published version

We develop a practical method to analyze the mixing structure of hadrons consisting of two components of quark-composite and hadronic composite. As an example we investigate the properties of the axial vector meson a1(1260) and discuss its mixing properties quantitatively. We also make reference to the large Nc procedure and its limitation for the classification of such a mixed state., Comment: 13 pages, 4 figures

In this paper, we briefly introduce the interests and the recent research activities on the \eta -mesic nuclei. We also mention the activities on the \eta ' (958)-mesic nucleus formation., Comment: Invited talk at the International Symposium on Mesic Nuclei, Krakow, 16 June 2010

The K^- induced production of Lambda(1405) in the K^- d to pi Sigma n reaction is investigated having in mind the conditions of the DAFNE facility at Frascati where kaons are obtained from the decay of slow moving phi mesons. We find that the K^- d to Lambda(1405) n process favors the production of Lambda(1405) initiated by the K^- p channel, which gives largest weight to the higher mass Lambda(1405) appearing at 1420 MeV in chiral theories. We find that the fastest kaons from the decay of the phi are well suited to see this resonance, particularly if one selects forward going neutrons in the center of mass, which reduce the contribution of single scattering and make the double scattering dominate where the signal of the resonance appears clearer., Comment: 6pages, 7 figures

We study the $K\Lambda(1405)$ configuration of the $K\bar{K}N$ system by considering $K\pi\Sigma$ as a coupled channel. We solve the Faddeev equations for these systems and find confirmation of the existence of a new $N^{*}$ resonance around 1920 MeV with $J^{\pi}=1/2^{+}$ predicted in a single-channel potential model and also found in a Faddeev calculation as an $a_{0}(980)N$ state, with the $a_{0}(980)$ generated in the $K\bar{K}$, $\pi\eta$ interaction., Comment: Published version

We study the structure of the sigma meson, the lowest-lying resonance of the pi pi scattering in the scalar-isoscalar channel, through the softening phenomena associated with the partial restoration of chiral symmetry. We build dynamical chiral models to describe the pi pi scattering amplitude, in which the sigma meson is described either as the chiral partner of the pion or as the dynamically generated resonance through the pi pi attraction. It is shown that the internal structure is reflected in the softening phenomena; the softening pattern of the dynamically generated sigma meson is qualitatively different from the behavior of the chiral partner of the pion. On the other hand, in the symmetry restoration limit, the dynamically generated sigma meson behaves similarly to the chiral partner., Comment: 10 pages, 2 figures, 1 table, talk give at HNP09, November 16-19, 2009, RCNP, Osaka University

The nature of the Lambda(1405) is discussed based on the unitarised coupled-channels approach with chiral dynamics (chiral unitary model). This approach describes the Kbar N scattering cross sections and the Lambda(1405) spectra phenomenologically very well. With this successful description of Lambda(1405), it is found that the Lambda(1405) is composed by two resonance states having different coupling nature to the meson-baryon states. As a consequence, the resonance position in the pi Sigma invariant mass spectrum depends on the initial channel of the Lambda(1405) production. To observe the Lambda(1405) initiated by the Kbar N channel, K^- d to Lambda(1405) n is one of the most favorable reactions. Hadronic molecule states with kaons are also discussed by emphasizing an important role of Lambda(1405) as a quasibound state of Kbar N., Comment: 8 pages, three figures. Talk given at 10th International Conference on Hypernuclear and Strange Particle Physics (HYP-X), Tokai, Ibaraki, Japan, 14-18 Sep 2009.

We determine the helicity amplitudes A_1/2 and radiative decay widths in the transition Lambda(1670) to gamma Y (Y=Lambda or Sigma^0). The Lambda(1670) is treated as a dynamically generated resonance in meson-baryon chiral dynamics. We obtain the radiative decay widths of the Lambda(1670) to gamma Lambda as 3 \pm 2 keV and to gamma Sigma^0 as 120 \pm 50 keV. Also, the Q^2 dependence of the helicity amplitudes A_1/2 is calculated. We find that the K Xi component in the Lambda(1670) structure, mainly responsible for the dynamical generation of this resonance, is also responsible for the significant suppression of the decay ratio Gamma_{gamma Lambda}/Gamma_{gamma Sigma^0}. A measurement of the ratio would, thus, provide direct access to the nature of the Lambda(1670). To compare the result for the Lambda(1670), we calculate the helicity amplitudes A_1/2 for the two states of the Lambda(1405). Also, the analytic continuation of Feynman parameterized integrals of more complicated loop amplitudes to the complex plane is developed which allows for an internally consistent evaluation of A_1/2., Comment: 15 pages, 8 figures

The QCD sum rule technique is employed to investigate pentaquark states with strangeness S = +1 and IJ^P = 0,1/2^\pm, 1,1/2^\pm, 0,3/2^\pm, 1,3/2^\pm. Throughout the calculation, emphasis is laid on the establishment of a valid Borel window, which corresponds to a region of the Borel mass, where the operator product expansion converges and the presumed ground state pole dominates the sum rules. Such a Borel window is achieved by constructing the sum rules from the difference of two independent correlators and by calculating the operator product expansion up to dimension 14. Furthermore, we discuss the possibility of the contamination of the sum rules by possible KN scattering states. As a result, we conclude that the 0,3/2^+ state seems to be the most probable candidate for the experimentally observed \Theta^+(1540), while we also obtain states with 0,1/2^-, 1,1/2^-, 1,3/2^+ at somewhat higher mass regions., Comment: 22 pages, 9 figures, 4 tables; typos corrected, reference added. Published in Phys. Rev. D

We present a theoretical study of the properties of the a1(1260) axial-vector resonance in a cold nuclear medium. In the vacuum, the a1(1260) resonance is generated dynamically from the interactions of a pseudoscalar and vector meson (rho pi and K barK*) in a coupled channel chiral unitary approach. Medium effects are implemented through the modification of the rho and pi propagators at finite nuclear density from well established microscopic many-body calculations. The in-medium pion spectral function accounts for the coupling to N-hole and Delta-hole excitations including short range correlations, whereas the in-medium rho incorporates modifications of its virtual pion cloud as well as direct resonance-hole excitations. The resulting in-medium a1(1260) exhibits significant broadening with increasing density as reflected in the rho pi scattering amplitude. The possible relation of our results with partial restoration of chiral symmetry in nuclear matter is discussed in terms of in-medium Weinberg sum rules., Comment: 22 pages, 9 figures, PTPTEX

In this talk I report on recent work related to the dynamical generation of baryonic resonances, some made up from pseudoscalar meson-baryon, others from vector meson-baryon and a third type from two meson-one baryon systems. We can establish a correspondence with known baryonic resonances, reinforcing conclusions previously drawn and bringing new light on the nature of some baryonic resonances of higher mass., Comment: Talk given at the Workshop on physics of the excited nucleon-NSTAR 2009, Beijing, april 2009

The K^- induced production of Lambda(1405) is investigated in K^- d to pi Sigma n reactions based on coupled-channels chiral dynamics, in order to discuss the resonance position of the Lambda(1405) in the KbarN channel. We find that the K^-d to Lambda(1405)n process favors the production of Lambda(1405) initiated by the KbarN channel. The present approach indicates that the Lambda(1405) resonance position is 1420 MeV rather than 1405 MeV in the pi Sigma invariant mass spectra of K- d to pi Sigma n reactions. This is consistent with an observed spectrum of the K^- d to pi^+ Sigma^- n with 686-844 MeV/c incident K^- by bubble chamber experiments done in the 70's. Our model also reproduces the measured Lambda(1405) production cross section., Comment: REVTeX, 12 page, 16 figures

The QCD sum rule method is formulated for the strangeness +1 pentaquark baryon with isospin I=0 and spin-parity J^P = 3/2^\pm. The spin-3/2 states are considered to be narrower than the spin-1/2 ones, and thus may provide a natural explanation for the experimentally observed narrow width of \Theta^+. In order to obtain reliable results in QCD sum rule calculations, we stress the importance of establishing a wide Borel window, where convergence of the operator product expansion and sufficient low-mass strength of the spectral function are guaranteed. To this end, we employ the difference of two independent correlators so that the high-energy continuum contribution is suppressed. The stability of the physical quantities against the Borel mass is confirmed within the Borel window. It is found that the sum rule gives positive evidence for the (I, J^P) = (0, 3/2^+) state with a mass of about 1.4 \pm 0.2 GeV, while we cannot extract any evidence for the (0, 3/2^-) state., Comment: 9 pages, 6 figures, 1 table. To be published in Phys. Rev. D

In this talk I review recent advances on the structure of the meson and baryon resonances which can be dynamically generated from the interaction of mesons or mesons and baryons. Particular emphasis is put on results involving vector mesons, which bring new light into the nature of some of the observed higher mass mesons and baryons and make predictions for new states., Comment: 6 pages, Talk at the PANIC2008 Conference

We study theoretically the in-flight ($K^-,N$) reactions for the formation of light kaonic nuclear systems to get deeper physical insights on the expected spectra, and to investigate the experimental feasibility of the reaction at new facilities like J-PARC. We show the expected spectra for the formation of the $K^-pp, K^-pn$, $K^-nn$ and $K^-$-$^{11}$B systems which are accessible by the ($K^-,N$) experiments. By considering the conversion part of the Green's function, we can show the missing mass spectra of the ($K^-,N$) reactions coincidence with the particle emissions due to ${\bar K}$ absorption in ${\bar K}N\to \pi Y$ processes. To calculate the cross sections, we use the so-called $T\rho$ approximation to evaluate the optical potential. As for the amplitude $T$, we adopt the chiral unitary amplitude of ${\bar K}N$ channel in vacuum for simplicity, and we also check the medium effects by applying the chiral amplitude at finite density. The effects of the p-wave optical potential of $\Sigma$(1385) channel and the contribution from ${\bar K^0}$ mixing in $^3$He($K^-,n$) reaction are also evaluated numerically. To understand the meanings of the spectrum shape, we also study the behavior of the poles of kaon Green's function in nuclear matter. We conclude that $^3$He($K^-,n$) and $^3$He($K^-,p$) reactions coincident with the $\pi\Sigma$ emission due to ${\bar K}$ absorption may show the certain structure in the bound region spectra indicating the existence of the unstable kaonic nuclear bound states. As for the $^{12}$C($K^-,p$) spectra with the $\pi\Sigma$ emission, we may also observe the structure in the bound region, however, we need to evaluate the medium effects carefully for larger nuclei., Comment: 14 pages, 12 figures

We calculate formation spectra of eta-nucleus systems in (pi,N) reactions with nuclear targets, which can be performed at existing and/or forthcoming facilities, including J-PARC, in order to investigate eta-nucleus interactions. Based on the N^*(1535) dominance in the eta N system, eta-mesic nuclei are suitable systems for study of in-medium properties of the N^*(1535) baryon resonance, such as reduction of the mass difference of N and N^* in nuclear medium, which affects level structure of the eta and N^*-hole modes. We find that clear information on the in-medium N^*- and eta-nucleus interactions can be obtained through the formation spectra of the eta-mesic nuclei. We also discuss the experimental feasibilities by showing several spectra of (pi,N) reactions calculated with possible experimental settings. Coincident measurements of pi N pairs from the N^* decays in nuclei help us to reduce backgrounds., Comment: 12 pages, 10 figures

We examine possibilities of pion condensation with zero momentum (s-wave condensation) in neutron stars by using the pion-nucleus optical potential U and the relativistic mean field (RMF) models. We use low-density phenomenological optical potentials parameterized to fit deeply bound pionic atoms or pion-nucleus elastic scatterings. Proton fraction (Y_p) and electron chemical potential (mu_e) in neutron star matter are evaluated in RMF models. We find that the s-wave pion condensation hardly takes place in neutron stars and especially has no chance if hyperons appear in neutron star matter and/or b_1 parameter in U has density dependence., Comment: 4 pages, 3 figures, REVTeX

The partial restoration of chiral symmetry in nuclear medium is investigated in a model independent way by exploiting operator relations in QCD. An exact sum rule is derived for the quark condensate valid for all density. This sum rule is simplified at low density to a new relation with the in-medium quark condensate *, in-medium pion decay constant F_{pi}^t and in-medium pion wave-function renormalization Z_{pi}*. Calculating Z_{pi}*at low density from the iso-scalar pion-nucleon scattering data and relating F_{pi}^t to the isovector pion-nucleus scattering length b_1^*, it is concluded that the enhanced repulsion of the s-wave isovector pion-nucleus interaction observed in the deeply bound pionic atoms directly implies the reduction of the in-medium quark condensate. The knowledge of the in-medium pion mass m_{pi}* is not necessary to reach this conclusion., Comment: 11 pages, 1 figures

We study the behavior with the number of colors ($N_c$) of the $\Lambda(1405)$ and $\Lambda(1670)$ resonances obtained dynamically within the chiral unitary approach. The leading order meson-baryon interaction, used as the kernel of the unitarization procedure, manifests a nontrivial $N_c$ dependence of the flavor SU(3) representation for baryons. As a consequence, the SU(3) singlet (or $\bar{K}N$) component of the $\Lambda(1405)$ states remains bound in the large $N_c$ limit, while the other components dissolve into the continuum. Introducing explicit SU(3) breaking, we obtain the $N_c$ dependence of the excitation energy, masses and widths of the physical $\Lambda(1405)$ and $\Lambda(1670)$ resonance. The $N_c$ behavior of the decay width is found to be different from the general counting rule for a $qqq$ state, indicating the dynamical origin of these resonances., Comment: 29 pages, 8 figures

The electric mean squared radii _E of Lambda(1405) are calculated in the chiral unitary model. We describe the Lambda(1405) as a dynamically generated resonance fully in the octet meson and octet baryon scattering. We also consider ``Lambda(1405)'' as a bound state of KbarN. For the later ``Lambda(1405),'' we obtain negative and larger absolute value of electric mean squared radius than that of ordinary baryons, which implies that Lambda(1405) have structure of widely spread K^- around p., Comment: 4 pages, 1 figure, use ws-mpla.cls. Talk given at Workshop on Chiral Symmetry in Hadron and Nuclear Physics: Chiral07, Osaka, Japan, 13-16 Nov 2007

We study eta meson properties in the infinite nuclear matter and in atomic nuclei with an emphasis on effects of the eta coupling to N*(1535)--nucleon-hole modes. The N*(1535) resonance, which dominates the low-energy eta-nucleon scattering, can be seen as a chiral partner of the nucleon. The change of the chiral mass gap between the N* and the nucleon in a nuclear medium has an impact on the properties of the eta-nucleus system. If the N*-nucleon mass gap decreases with a density increase (chiral symmetry restoration) the calculations show the existence of the resonance state at the energy about 60 MeV and two bound eta-nucleus states with the binding energies about -80 MeV. These states can have strong effect on predicted cross sections of the ^12C (gamma,p) ^11B reaction with eta-meson production., Comment: 22 pages, 12 figures

We discuss how electromagnetic properties provide useful tests of the nature of resonances, and we study these properties for the N*(1535) which appears dynamically generated from the strong interaction of mesons and baryons. Within this coupled channel chiral unitary approach, we evaluate the A_1/2 and S_1/2 helicity amplitudes as a function of Q^2 for the electromagnetic N*(1535) to gamma* N transition. Within the same formalism we evaluate the cross section for the reactions gamma N to eta N. We find a fair agreement for the absolute values of the transition amplitudes, as well as for the Q^2 dependence of the amplitudes, within theoretical and experimental uncertainties discussed in the paper. The ratios obtained between the S_1/2 and A_1/2 for the neutron or proton states of the N*(1535) are in qualitative agreement with experiment and there is agreement on the signs. The same occurs for the ratio of cross sections for the eta photoproduction on neutron and proton targets in the vicinity of the N*(1535) energy. The global results support the idea of this resonance as being dynamically generated, hence, largely built up from meson baryon components. However, the details of the model indicate that an admixture with a genuine quark state is also demanded that could help obtain a better agreement with experimental data., Comment: 19 pages, 16 figures, REVTeX

In these lectures I will show some results obtained with the chiral unitary approach applied to the photo and electroproduction of mesons. The results for photoproduction of $\eta \pi^0 p$ and $K^0 \pi^0 \Sigma^+$, together with related reactions will be shown, having with common denominator the excitation of the $\Delta(1700)$ resonance which is one of those dynamically generated in the chiral unitary approach. Then I will show results obtained for the $e^+ e^- \to \phi f_0(980)$ reaction which reproduce the bulk of the data except for a pronounced peak, giving support to a new mesonic resonance, X(2175). Results will also be shown for the electromagnetic form factors of the $N^*(1535)$ resonance, also dynamically generated in this approach. Finally, I will show some results on the photoproduction of the $\omega$ in nuclei, showing that present experimental results claiming a shift of the $\omega$ mass in the medium are tied to a particular choice of background and are not conclusive. One the other hand, the same experimental results show unambiguously a huge increase of the $\omega$ width in the nuclear medium., Comment: Lecture at the "International School of Nuclear Physics", 29th Course Quarks in Hadrons and Nuclei, Erice, Italy, September 2007. Note added in Proofs concerning the mixed events technique and other comments on omega production

Exploiting operator relations in QCD, we derive a novel and model-independent formula relating the in-medium quark condensate * to the decay constant F*_t and the wave function renormalization constant Z* of the pion in the nuclear medium. Evaluating Z* at low density from the iso-scalar pion-nucleon scattering data, it is concluded that the enhanced repulsion of the s-wave isovector pion-nucleusinteraction observed in the deeply bound pionic atoms implies directly the reduction of the in-medium quark condensate. The knowlege of the in-medium pion mass is not necessary to reach this conclusion., Comment: 4 pages, Talk given at the Yukawa International Seminar (YKIS) 2006, "New frontiers in QCD -- Exotic hadrons and hadronic matter", Kyoto, Japan, 20 Nov. - 8 Dec. 2006. To be published in Supplemet of Prog. Theor. Phys

We present a theoretical study on formation rates of \eta and \omega meson-nucleus systems induced by (\gamma,p) reactions on nuclear targets at ideal recoilless condition. We find that the smaller distortion effect in the (\gamma,p) reaction enables us to investigate properties of the mesons created deeply inside nucleus more clearly. We also consider excitation of scalar-isoscalar (\sigma) mode in nucleus in order to investigate spectral enhancement around two-pion threshold caused by partial restoration of chiral symmetry. We conclude that valuable information of meson-nucleus interactions can be extracted from global structure of the missing mass spectra in the (\gamma,p) reaction., Comment: 38 pages, 3 tables, 12 figures, submitted to Nucl.Phys.A, minor corrections, added several references