Recent topics of mesic atoms and mesic nuclei -- ϕ\phi mesic nuclei exist ?--

We study $\phi$-meson production in nuclei to investigate the in-medium modification of the $\phi$-meson spectral function at finite density. We consider (${\bar p},\phi$), ($\gamma,p$) and ($\pi^-,n$) reactions to produce a $\phi$-meson inside the nucleus and evaluate the effects of the medium modifications to reaction cross sections. The structures of the bound states, $\phi$-mesic nuclei, are also studied. For strong absorptive interaction cases, we need to know the spectrum shape in a wide energy region to deduce the properties of $\phi$.Comment: Talk given at EXA08, Vienna, September 2008. To be published in the Proceedings, Hyperfine Interactions. 6 pages, 6 figure

Quantum Hall States of Gluons in Quark Matter

We have recently shown that dense quark matter possesses a color ferromagnetic phase in which a stable color magnetic field arises spontaneously. This ferromagnetic state has been known to be Savvidy vacuum in the vacuum sector. Although the Savvidy vacuum is unstable, the state is stabilized in the quark matter. The stabilization is achieved by the formation of quantum Hall states of gluons, that is, by the condensation of the gluon's color charges transmitted from the quark matter. The phase is realized between the hadronic phase and the color superconducting phase. After a review of quantum Hall states of electrons in semiconductors, we discuss the properties of quantum Hall states of gluons in quark matter in detail. Especially, we evaluate the energy of the states as a function of the coupling constant. We also analyze solutions of vortex excitations in the states and evaluate their energies. We find that the states become unstable as the gauge coupling constant becomes large, or the chemical potential of the quarks becomes small, as expected. On the other hand, with the increase of the chemical potential, the color superconducting state arises instead of the ferromagnetic state. We also show that the quark matter produced by heavy ion collisions generates observable strong magnetic field $\sim 10^{15}$ Gauss when it enters the ferromagnetic phase.Comment: 11 pages, 2 figure

Model-independent study of the QCD sum rule for the pi NN coupling constant

We reinvestigate the QCD sum rule for the pi NN coupling constant, g, starting from the vacuum-to-pion matrix element of the correlation function of the interpolating fields of two nucleons. We study in detail the physical content of the correlation function without referring to the effective theory. We consider the invariant correlation functions by splitting the correlation function into different Dirac structures. We show that the coefficients of the double-pole terms are proportional to g but that the coefficients of the single-pole terms are not determined by g. In the chiral limit the single-pole terms as well as the continuum terms are ill defined in the dispersion integral. Therefore, the use of naive QCD sum rules obtained from the invariant correlation functions is not justified. A possible procedure to avoid this difficulty is discussed.Comment: 20 pages, 2 figure

eta-prime nucleus optical potential and possible eta-prime bound states

Starting from a recent model of the eta'N interaction, we evaluate the eta'-nucleus optical potential, including the contribution of lowest order in density, t rho/2m_eta', together with the second order terms accounting for eta' absorption by two nucleons. We also calculate the formation cross section of the eta' bound states from (pi+,p) reactions on nuclei. The eta'-nucleus potential suffers from uncertainties tied to the poorly known eta'N interaction, which can be partially constrained by the experimental modulus of the eta'N scattering length and/or the recently measured transparency ratios in eta' nuclear photoproduction. Assuming an attractive interaction and taking the claimed experimental value |a_eta'N| = 0.1 fm, we obtain a eta' optical potential in nuclear matter at saturation density of V_eta' = -(8.7 + 1.8i) MeV, not attractive enough to produce eta' bound states in light nuclei. Larger values of the scattering length give rise to deeper optical potentials, with moderate enough imaginary parts. For a value |a_eta'| = 0.3 fm, which can still be considered to lie within the uncertainties of the experimental constraints, the spectra of light and medium nuclei show clear structures associated to eta'-nuclear bound states and to threshold enhancements in the unbound region.Comment: 11 pages, 4 figures, 2 table

eta-Nucleus interactions and in-medium properties of N*(1535) in chiral models

The properties of eta-nucleus interaction and their experimental consequences are investigated with eta-nucleus optical potentials obtained by postulating the N*(1535) dominance for eta-N system. The N*(1535) properties in nuclear medium are evaluated by two kinds of chiral effective models based on distinct pictures of N*(1535). We find that these two models provide qualitatively different optical potentials of the eta meson, reflecting the in-medium properties of N*(1535) in these models. In order to compare these models in physical observables, we calculate spectra of (d,3He) reactions for the eta mesic nucleus formation with various kinds of target nuclei. We show that the (d,3He) spectra obtained in these models are significantly different and are expected to be distinguishable in experiments.Comment: 24 pages, 8 figure

Level crossing of particle-hole and mesonic modes in eta mesic nuclei

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 figure