arXiv subjects
Publications and source records attributed to O. Morimatsu.
We investigate the effects of baryon chemical potential μon the shear viscosity coefficient ηand the viscosity to entropy density ratio η/s of a pion-nucleon gas mixture. We find that ηis an increasing function of T and μ, while the ratio η/s turns to a decreasing function in a wide region of T-μplane. In the kinematical region we studied, the smallest value of η/s is about 0.3.
Possibility of an axial vector isoscalar tetraquark with $ud\bar{s}\bar{s}$ is discussed. If the pentaquark $Θ^+(1540)$ has the $(qq)_{\bar{3}}(qq)_{\bar{3}}\bar{q}$ configuration, the isoscalar $ud\bar{s}\bar{s}$($\vartheta^+$-meson) state with $J^P=1^+$ is expected to exist in the mass region lower than or close to the mass of $Θ^+(1540)$. Within a flux-tube quark model, a possible resonant state of $ud\bar{s}\bar{s}(J^{P}=1^{+})$ is suggested to appear around 1.4 GeV with the width ${\cal{O}}(20\sim 50)$ MeV. We propose that the $\vartheta^+$-meson is a good candidate for the tetraquark search, which would be observed in the $K^+K^+π^-$ decay channel.
The exotic baryon $Θ^+(uudd\bar{s})$ is studied with microscopic calculations in a quark model by using a method of antisymmetrized molecular dynamics. We predict that the lowest even state is $J^π=1/2^+(I=0)$ or $J^π=3/2^+(I=0)$, and the lowest odd state is $J^π=3/2^-(I=1)$. They nearly degenerate in the $uudd\bar{s}$ system. We discuss $K^+n$ decay widths and estimate them to be $Γ< 7$ for the $J^π=\{1/2^+,3/2^+\}$, and $Γ<1$ MeV for the $J^π=3/2^-$ state.
The exotic baryon $Θ^+(uudd\bar{s})$ is studied with microscopic calculations in a quark model by using a method of antisymmetrized molecular dynamics(AMD). We predict narrow states, $J^π=1/2^+(I=0)$, $J^π=3/2^+(I=0)$, and $J^π=3/2^-(I=1)$, which nearly degenerate in a low-energy region of the $uudd\bar{s}$ system. We discuss $NK$ decay widths and estimate them to be $Γ< 7$ for the $J^π=\{1/2^+,3/2^+\}$, and $Γ<1$ MeV for the $J^π=3/2^-$ state.
We show a possibility that a color ferromagnetic state exists in SU(3) gauge theory of quark matter with two flavors. Although the state involves three types of unstable modes of gluons, all of these modes are stabilized by forming a quantum Hall state of one of the modes. We also show that at large chemical potential, a color superconducting state (2SC) appears even in the ferromagnetic state. This is because Meissner effect by condensed anti-triplet quark pairs does not work on the magnetic field in the ferromagnetic state.
The QCD sum rules for spin-dependent nucleon-nucleon interactions are formulated and their physical implications are studied. The basic object of the study is the correlation function of the nucleon interpolating field, where the matrix element is taken with respect to the one-nucleon state. The dispersion integral of the correlation function around the nucleon threshold is investigated in detail. It turns out that the integral can be identified as a measure of the nucleon-nucleon interaction strength, which is proportional to the scattering length in the small scattering length limit and to one half of the effective range in the large scattering length limit. New operators must be taken into account in the OPE of the correlation function. There behavior operators do not vanish when the matrix element is taken with respect to the spin-nonaveraged one-nucleon state. The Wilson coefficients of such operators are calculated. The sum rules obtained in this manner relate the spin-dependent nucleon-nucleon interaction strengths with the spin-dependent nucleon matrix elements of the quark-gluon composite operators. The sum rules imply that the interaction is stronger in the spin-triplet channel than in the spin-singlet channel, but that the spin-dependence of the nucleon-nucleon interactions is rather small. In the spin-singlet channel the calculated strength is in qualitative agreement with the empirical strength, which is estimated by the empirical low energy scattering observables.
The pion-nucleon and kaon-nucleon scattering lengths are studied in the QCD sum rule. We show that the leading and next-to-leading order terms of the OPE give rise to the Tomozawa-Weinberg and sigma terms, respectively. We also show that in the kaon-nucleon system the $Λ(1405)$ contribution has to be subtracted from the OPE side in order to obtain the scattering length. The odd components of the $T$-matrices are in agreement with the experimental values not only in the pion-nucleon channel but also in the kaon-nucleon channel after the $Λ(1405)$ contribution subtracted. The even components disagree with the experimental values in the pion-nucleon channel, which is similar to the situation in the PCAC-plus-current-algebra approach at the Weinberg point. We speculate that this discrepancy should be explained by the continuum contribution in the spectral function above the pion-nucleon threshold.