Physical Review Letters

Avron, J. E; Sadun, L. E; Segert, J. E; Simon, B. E

doi: 10.1103/PhysRevLett.61.1329pmid: 10038766

We discuss topological invariants for Fermi systems that have time-reversal invariance. The TK N 2 integers (first Chern numbers) are replaced by second Chern numbers, and Berry's phase becomes a unit quaternion, or equivalently an element of SU(2). The canonical example playing much the same role as spin ½ in a magnetic field is spin ½ in a quadrupole electric field. In particular, the associated bundles are nontrivial and have ± 1 second Chern number. The connection that governs the adiabatic evolution coincides with the symmetric SU(2) Yang-Mills instanton.

Edwards, Robert G

doi: 10.1103/PhysRevLett.61.1333pmid: 10038767

We discuss the problem of solving large linear systems of equations that arise in lattice systems with disorder. Three examples of this kind of problem are (i) computing currents in a random-resistor network, (ii) computing the fermion (quark) propagator in lattice quantum chromodynamics, and (iii) the discrete Schrödinger operator with a random potential (the Anderson model of localization). We show that the algebraic multigrid is a very effective way to compute currents in a random-resistor network. It is likely that similar techniques will apply to the other problems.

Whiting, Bernard F; York, James W

doi: 10.1103/PhysRevLett.61.1336pmid: 10038768

Statistical mechanics of gravitational fields describing the black-hole topological sector, and the correspondence to thermodynamics, are considered. The Euclidean action is evaluated on the constraint hypersurface and a measure is obtained, resulting in a path-integral form of the canonical partition function. We obtain the usual black-hole entropy plus quantum corrections when the temperature and size of the system are appropriate. Under other conditions, we give evidence for the existence of a phase transition (change of topology).

Speake, C. C; Quinn, T. J

doi: 10.1103/PhysRevLett.61.1340pmid: 10038769

We present the results of an experiment, carried out using a beam balance, designed to search for a short-range, isospin-coupling component of the fifth force. The value for the coupling constant ξ was found to be (0.8 ± 2.0) × 10 - 2 . The significance of this result is discussed with reference to other recently published work.

Mattis, Michael P; Mukerjee, Madhusree P

doi: 10.1103/PhysRevLett.61.1344pmid: 10038770

Quasielastic meson-baryon scattering is reformulated in t -channel language (meson exchange) instead of s -channel language (baryon-resonance formation), by use of skyrmion methods. A new selection rule emerges, valid to leading order in large N c . The isospin of the exchanged state must equal its total angular momentum (spin+orbital). Differences between the two-flavor and the three-flavor approach are discussed.

Taras, P; Flibotte, S; Gascon, J; Haas, B; Pilotte, S; Radford, D. C; Ward, D. C; Andrews, H. R; Ball, G. C; Banville, F. C; Cournover, S. C; Horn, D. C; Johansson, J. K; Monaro, S. K; Nadon, N. K; Prevost, D. K; Pruneau, C. K;

Müller, A; Hofmann, G; Tinschert, K; Salzborn, E

doi: 10.1103/PhysRevLett.61.1352pmid: 10038772

In electron-impact ionization of C 3 + ions we found the first unambiguous experimental evidence for resonant-excitation auto-double-ionization processes. These involve capture of the projectile electron by the ion with simultaneous K -shell excitation and subsequent emission of two correlated electrons. The resonance strength measured for the 1 s 2 s 2 2 p P 3 contribution is (2.0 ± 0.4) × 10 - 20 cm 2 eV. In addition, we resolved individual thresholds of excitation autoionization via states 1 s 2 s 2 l and identified other resonant contributions to net single ionization.

Barton, John J

doi: 10.1103/PhysRevLett.61.1356pmid: 10038773

A photoelectron hologram is a two-angle photoelectron diffraction pattern: Direct photoemission plays the role of the reference wave and the scattered waves are the object waves. When the hologram is created from the core-level photoemission of single emitting species on an ordered surface, a complete three-dimensional image of the surface structure surrounding the emitter can be reconstructed by Fourier transformation.

Cheung, P. Y; Donovan, S. Y; Wong, A. Y

doi: 10.1103/PhysRevLett.61.1360pmid: 10038774

The transition to chaos through intermittency has been observed in a steady-state plasma system. Results from real-time signals, spectral analysis, and constructed Poincaré sections are used to confirm the existence of intermittency. Low-frequency 1 f -type noise is also observed during the onset of chaos.

Parks, P. B

doi: 10.1103/PhysRevLett.61.1364pmid: 10038775

It is shown that transverse injection of a hypervelocity high-density spheromak plasmoid into a tokamak plasma may be a viable fueling scheme. Three important processes occur and are discussed individually: establishment of equilibrium, slowing down, and disassembly of the compact toroid.