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

Fermi Liquids and the Luttinger Integral

The Luttinger Theorem, which relates the electron density to the volume of the Fermi surface in an itinerant electron system, is taken to be one of the essential features of a Fermi liquid. The microscopic derivation of this result depends on the vanishing of a certain integral, the Luttinger integral $I_{\rm L}$, which is also the basis of the Friedel sum rule for impurity models, relating the impurity occupation number to the scattering phase shift of the conduction electrons. It is known that non-zero values of $I_{\rm L}$ with $I_{\rm L}=\pm\pi/2$, occur in impurity models in phases with non-analytic low energy scattering, classified as singular Fermi liquids. Here we show the same values, $I_{\rm L}=\pm\pi/2$, occur in an impurity model in phases with regular low energy Fermi liquid behavior. Consequently the Luttinger integral can be taken to characterize these phases, and the quantum critical points separating them interpreted as topological.Comment: 5 pages 7 figure

Axial vector tetraquark with S=+2

Possibility of an axial vector isoscalar tetraquark with $ud\bar{s}\bar{s}$ is discussed. If the pentaquark $\Theta^+(1540)$ 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 $\Theta^+(1540)$. 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 $K^+K^+\pi^-$ decay channel.Comment: 20 pages, 5 figures, submitted to Phys.Rev.

Ion dynamics and acceleration in relativistic shocks

Ab-initio numerical study of collisionless shocks in electron-ion unmagnetized plasmas is performed with fully relativistic particle in cell simulations. The main properties of the shock are shown, focusing on the implications for particle acceleration. Results from previous works with a distinct numerical framework are recovered, including the shock structure and the overall acceleration features. Particle tracking is then used to analyze in detail the particle dynamics and the acceleration process. We observe an energy growth in time that can be reproduced by a Fermi-like mechanism with a reduced number of scatterings, in which the time between collisions increases as the particle gains energy, and the average acceleration efficiency is not ideal. The in depth analysis of the underlying physics is relevant to understand the generation of high energy cosmic rays, the impact on the astrophysical shock dynamics, and the consequent emission of radiation.Comment: 5 pages, 3 figure

Anti-prion activity of an RNA aptamer and its structural basis.

Prion proteins (PrPs) cause prion diseases, such as bovine spongiform encephalopathy. The conversion of a normal cellular form (PrP(C)) of PrP into an abnormal form (PrP(Sc)) is thought to be associated with the pathogenesis. An RNA aptamer that tightly binds to and stabilizes PrP(C) is expected to block this conversion and to thereby prevent prion diseases. Here, we show that an RNA aptamer comprising only 12 residues, r(GGAGGAGGAGGA) (R12), reduces the PrP(Sc) level in mouse neuronal cells persistently infected with the transmissible spongiform encephalopathy agent. Nuclear magnetic resonance analysis revealed that R12, folded into a unique quadruplex structure, forms a dimer and that each monomer simultaneously binds to two portions of the N-terminal half of PrP(C), resulting in tight binding. Electrostatic and stacking interactions contribute to the affinity of each portion. Our results demonstrate the therapeutic potential of an RNA aptamer as to prion diseases

Acceleration in perpendicular relativistic shocks for plasmas consisting of leptons and hadrons

We investigate the acceleration of light particles in perpendicular shocks for plasmas consisting of a mixture of leptonic and hadronic particles. Starting from the full set of conservation equations for the mixed plasma constituents, we generalize the magneto-hydrodynamical jump conditions for a multi-component plasma, including information about the specific adiabatic constants for the different species. The impact of deviations from the standard model of an ideal gas is compared in theory and particle-in-cell simulations, showing that the standard-MHD model is a good approximation. The simulations of shocks in electron-positron-ion plasmas are for the first time multi-dimensional, transverse effects are small in this configuration and 1D simulations are a good representation if the initial magnetization is chosen high. 1D runs with a mass ratio of 1836 are performed, which identify the Larmor frequency \omega_{ci} as the dominant frequency that determines the shock physics in mixed component plasmas. The maximum energy in the non-thermal tail of the particle spectra evolves in time according to a power-law proportional to t^\alpha with \alpha in the range 1/3 < \alpha < 1, depending on the initial parameters. A connection is made with transport theoretical models by Drury (1983) and Gargate & Spitkovsky (2011), which predict an acceleration time proportional to \gamma and the theory for small wavelength scattering by Kirk & Reville (2010), which predicts a behavior rather as proportional to \gamma^2. Furthermore, we compare different magnetic field orientations with B_0 inside and out of the plane, observing qualitatively different particle spectra than in pure electron-ion shocks