Narrow Pentaquark States in a Quark Model with Antisymmetrized Molecular Dynamics

The exotic baryon $\Theta^+(uudd\bar{s})$ is studied with microscopic calculations in a quark model by using a method of antisymmetrized molecular dynamics(AMD). We predict narrow states, $J^\pi=1/2^+(I=0)$, $J^\pi=3/2^+(I=0)$, and $J^\pi=3/2^-(I=1)$, which nearly degenerate in a low-energy region of the $uudd\bar{s}$ system. We discuss $NK$ decay widths and estimate them to be $\Gamma< 7$ for the $J^\pi=\{1/2^+,3/2^+\}$, and $\Gamma<1$ MeV for the $J^\pi=3/2^-$ state.Comment: Talk given at International Workshop on PENTAQUARK04, Spring-8, Hyogo, Japan, 20-23 Jul 200

The emission of energetic electrons from the complex streamer corona adjacent to leader stepping

We here propose a model to capture the complexity of the streamer corona adjacent to leader stepping and relate it to the production of energetic electrons serving as a source of X-rays and $\gamma$-rays, manifesting in terrestrial gamma-ray flashes (TGFs). During its stepping, the leader tip is accompanied by a corona consisting of multitudinous streamers perturbing the air in its vicinity and leaving residual charge behind. We explore the relative importance of air perturbations and preionization on the production of energetic run-away electrons by 2.5D cylindrical Monte Carlo particle simulations of streamers in ambient fields of 16 kV cm$^{-1}$ and 50 kV cm$^{-1}$ at ground pressure. We explore preionization levels between $10^{10}$ m$^{-3}$ and $10^{13}$ m$^{-3}$, channel widths between 0.5 and 1.5 times the original streamer widths and air perturbation levels between 0\% and 50\% of ambient air. We observe that streamers in preionized and perturbed air accelerate more efficiently than in non-ionized and uniform air with air perturbation dominating the streamer acceleration. We find that in unperturbed air preionization levels of $10^{11}$ m$^{-3}$ are sufficient to explain run-away electron rates measured in conjunction with terrestrial gamma-ray flashes. In perturbed air, the production rate of runaway electrons varies from $10^{10}$ s$^{-1}$ to $10^{17}$ s$^{-1}$ with maximum electron energies from some hundreds of eV up to some hundreds of keV in fields above and below the breakdown strength. In the presented simulations the number of runaway electrons matches with the number of energetic electrons measured in alignment with the observations of terrestrial gamma-ray flashes. Conclusively, the complexity of the streamer zone ahead of leader tips allows explaining the emission of energetic electrons and photons from streamer discharges.Comment: 29 pages, 11 figures, 2 table

Two-pion bound state in sigma channel at finite temperature

We study how we can understand the change of the spectral function and the pole location of the correlation function for sigma at finite temperature, which were previously obtained in the linear sigma model with a resummation technique called optimized perturbation theory. There are two relevant poles in the sigma channel. One pole is the original sigma pole which shows up as a broad peak at zero temperature and becomes lighter as the temperature increases. The behavior is understood from the decreasing of the sigma condensate, which is consistent with the Brown-Rho scaling. The other pole changes from a virtual state to a bound state of pion-pion as the temperature increases which causes the enhancement at the pion-pion threshold. The behavior is understood as the emergence of the pion-pion bound state due to the enhancement of the pion-pion attraction by the induced emission in medium. The latter pole, not the former, eventually degenerates with pion above the critical temperature of the chiral transition. This means that the observable "sigma" changes from the former to the latter pole, which can be interpreted as the level crossing of "sigma" and pion-pion at finite temperature.Comment: 4 pages, 4 figure

Flavor Mass and Mixing and S_3 Symmetry -- An S_3 Invariant Model Reasonable to All --

We assume that weak bases of flavors (u, c)_{L,R}, (d,s)_{L,R}, (e, \mu) _{L,R}, (\nu_e, \nu_\mu)_{L,R} are the S_3 doublet and t_{L,R}, b_{L,R}, \tau_{L,R}, {\nu_\tau}_{L,R} are the S_3 singlet and further there are S_3 doublet Higgs (H_D^1, H_D^2) and S_3 singlet Higgs H_S. We suggest an S_3 invariant Yukawa interaction, in which masses caused from the interaction of S_3 singlet flavors and Higgs is very large and masses caused from interactions of S_3 doublet flavors and Higgs are very small, and the vacuum expectation value _0 is rather small compared to the _0. In this model, we can explain the quark sector mass hierarchy, flavor mixing V_{CKM} and measure of CP violation naturally. The leptonic sector mass hierarchy and flavor mixing described by V_{MNS} having one-maximal and one-large mixing character can also be explained naturally with no other symmetry restriction. In our model, an origin of Cabibbo angle is the ratio \lambda=_0 /_0 and an origin of CP violation is the phase of H_D^1.Comment: 16 page

Mixings of 4-quark components in light non-singlet scalar mesons in QCD sum rules

Mixings of 4-quark components in the non-singlet scalar mesons are studied in the QCD sum rules. We propose a formulation to evaluate the cross correlators of q\bar q and qq\bar q \bar q operators and to define the mixings of different Fock states in the sum rule. It is applied to the non-singlet scalar mesons, a_0 and K_0^\ast. It is found that the 4-quark operators predict lower masses than the q\bar q operators and that the 4-quark states occupy about 70-90% of the lowest mass states.Comment: 8 pages, 9 figure

Evolution of the electronic structure from electron-doped to hole-doped states in the two-dimensional Mott-Hubbard system La1.17-xPbxVS3.17

The filling-controlled metal-insulator transition (MIT) in a two-dimensional Mott-Hubbard system La1.17-xPbxVS3.17 has been studied by photoemission spectroscopy. With Pb substitution x, chemical potential mu abruptly jumps by ~ 0.07 eV between x=0.15 and 0.17, indicating that a charge gap is opened at x ~= 0.16 in agreement with the Mott insulating state of the d2 configuration. When holes or electrons are doped into the Mott insulator of x ~= 0.16, the gap is filled and the photoemission spectral weight at mu, rho(mu), gradually increases in a similar way to the electronic specific heat coefficient, although the spectral weight remains depressed around mu compared to that expected for a normal metal, showing a pseudogap behavior in the metallic samples. The observed behavior of varrho(mu)->0 for x->0.16 is contrasted with the usual picture that the electron effective mass of the Fermi-liquid system is enhanced towards the metal-insulator boundary. With increasing temperature, the gap or the pseudogap is rapidly filled up, and the spectra at T=300 K appears to be almost those of a normal metal. Near the metal-insulator boundary, the spectra around mu are consistent with the formation of a Coulomb gap, suggesting the influence of long-range Coulomb interaction under the structural disorder intrinsic to this system.Comment: 8 pages, 12 figure

3-D General Relativistic MHD Simulations of Generating Jets

We have performed a first fully 3-D GRMHD simulation with Schwarzschild black hole with a free falling corona. The initial simulation results show that a jet is created as in previous axisymmetric simulations. However, the time to generate the jet is longer than in the 2-D simulations. We expect that due to the additional azimuthal dimension the dynamics of jet formation can be modified.Comment: 4 pages Proc. Oxford Radio Galaxy Workshop ed. R. Laing & K. Blundell (San Francisco: PASP) in press (revised