On the Existence of Heavy Pentaquarks: The large Nc and Heavy Quark Limits and Beyond

We present a very general argument that the analogue of a heavy pentaquark (a state with the quantum numbers of a baryon combined with an additional light quark and a heavy antiquark) must exist as a particle stable under strong interactions in the combined heavy quark and large Nc limits of QCD. Moreover, in the combined limit these heavy pentaquark states fill multiplets of SU(4)xO(8)xSU(2). We explore the question of whether corrections in the combined 1/Nc and 1/mQ expansions are sufficiently small to maintain this qualitative result. Since no model-independent way is known to answer this question, we use a class of ``realistic'' hadronic models in which a pentaquark can be formed via nucleon-heavy meson binding through a pion-exchange potential. These models have the virtue that they necessarily yield the correct behavior in the combined limit, and the long-distance parts of the interactions are model independent. If the long-distance attraction in these models were to predict bound states in a robust way (i.e., largely insensitive to the details of the short-range interaction), then one could safely conclude that heavy pentaquarks do exist. However, in practice the binding does depend very strongly on the details of the short-distance physics, suggesting that the real world is not sufficiently near the combined large Nc, mQ limit to use it as a reliable guide. Whether stable heavy pentaquarks exist remains an open question.Comment: 11 pages; references adde

High pressure effects in fluorinated HgBa2Ca2Cu3O(8+d)

We have measured the pressure sensitivity of Tc in fluorinated HgBa2Ca2Cu3O(8+d) (Hg-1223) ceramic samples with different F contents, applying pressures up to 30 GPa. We obtained that Tc increases with increasing pressure, reaching different maximum values, depending on the F doping level, and decreases for a further increase of pressure. A new high Tc record (166 K +/- 1 K) was achieved by applying pressure (23 GPa) in a fluorinated Hg-1223 sample near the optimum doping level. Our results show that all our samples are at the optimal doping, and that fluorine incorporation decreases the crystallographic $a$-parameter concomitantly increasing the maximum attainable Tc. This effect reveals that the compression of the $a$ axes is one of the keys that controls the Tc of high temperature superconductors.Comment: 4 pages, 4 figures, submitted to Phys. Rev.

Dynamics of Majorana-based qubits operated with an array of tunable gates

We study the dynamics of Majorana zero modes that are shuttled via local tuning of the electrochemical potential in a superconducting wire. By performing time-dependent simulations of microscopic lattice models, we show that diabatic corrections associated with the moving Majorana modes are quantitatively captured by a simple Landau-Zener description. We further simulate a Rabi-oscillation protocol in a specific qubit design with four Majorana zero modes in a single wire and quantify constraints on the timescales for performing qubit operations in this setup. Our simulations utilize a Majorana representation of the system, which greatly simplifies simulations of superconductors at the mean-field level.Comment: 12 pages, 8 figures. v2: minor corrections, updated reference

Quasi-Two-Dimensional Dynamics of Plasmas and Fluids

In the lowest order of approximation quasi-twa-dimensional dynamics of planetary atmospheres and of plasmas in a magnetic field can be described by a common convective vortex equation, the Charney and Hasegawa-Mirna (CHM) equation. In contrast to the two-dimensional Navier-Stokes equation, the CHM equation admits "shielded vortex solutions" in a homogeneous limit and linear waves ("Rossby waves" in the planetary atmosphere and "drift waves" in plasmas) in the presence of inhomogeneity. Because of these properties, the nonlinear dynamics described by the CHM equation provide rich solutions which involve turbulent, coherent and wave behaviors. Bringing in non ideal effects such as resistivity makes the plasma equation significantly different from the atmospheric equation with such new effects as instability of the drift wave driven by the resistivity and density gradient. The model equation deviates from the CHM equation and becomes coupled with Maxwell equations. This article reviews the linear and nonlinear dynamics of the quasi-two-dimensional aspect of plasmas and planetary atmosphere starting from the introduction of the ideal model equation (CHM equation) and extending into the most recent progress in plasma turbulence.U. S. Department of Energy DE-FG05-80ET-53088Ministry of Education, Science and Culture of JapanFusion Research Cente

Positive parity pentaquark towers in large Nc QCD

We construct the complete set of positive parity pentaquarks, which correspond in the quark model to {\bar s} q^{Nc+1} states with one unit of orbital angular momentum L=1. In the large Nc limit they fall into the K=1/2 and K=3/2 irreps (towers) of the contracted SU(4)c symmetry. We derive predictions for the mass spectrum and the axial couplings of these states at leading order in 1/Nc. The strong decay width of the lowest-lying positive parity exotic state is of order O(1/Nc), such that this state is narrow in the large Nc limit. Replacing the antiquark with a heavy antiquark {\bar Q} q^{Nc+1}, the two towers become degenerate, split only by O(1/mQ) hyperfine interactions. We obtain predictions for the strong decay widths of heavy pentaquarks to ordinary baryons and heavy H(*)_{\bar Q} mesons at leading order in 1/Nc and 1/mQ.Comment: 21 pages, 2 figures, 5 table