A random-walk representation for continuum scalar quantum electrodynamics in the Feynman gauge is derived. The triviality problem of scalar QED is formulated in terms of the triviality of magnetic random-walk interactions. The average partition function z of a pair of magnetic random walks is shown to be equal to 1 for D≥4.

We present data for the QCD β function with two flavors of light Wilson fermions. We use the hybrid Monte Carlo algorithm and the method of matching of ratios of products of Wilson loops. At β=6/${\mathrm{g}}^2$=6.0 perturbative scaling has not yet set in, whereas at β=6.8 it clearly has. Since the matching is done for the integral of the β function this scaling is expected above β=6.0. .AE

From 85±10 examples of the decay ${\mathrm{\Xi }}^0$ → ${\mathrm{\Sigma }}^0$γ we have measured the decay branching ratio Γ(${\mathrm{\Xi }}^0$ → ${\mathrm{\Sigma }}^0$γ)/Γ(${\mathrm{\Xi }}^0$ → Λ${\mathrm{\pi }}^0$) =[3.56±0.42(stat)±0.10(syst)]×${10}^{\mathrm{-}3}$ and the asymmetry parameter α(${\mathrm{\Xi }}^0$ → ${\mathrm{\Sigma }}^0$γ) =0.20±0.32(stat)±0.05(syst).

We have measured the cross section for radiative capture of thermal neutrons on ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. The measured cross section of 54±6 μb is used to estimate the astrophysical S factor for the reaction ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(p,$e^{+}$ν${)}^4$He which gives rise to high-energy neutrinos from the Sun.

The photon-photon scattering of intense laser radiation predicted by QED can give rise to second-harmonic generation in a dc magnetic field due to broken symmetry of the interaction. The laser energy required to observe this effect can be achieved by using available laser facilities and the state-of-the-art photon-counting technology.

We have observed viscous fingering flow in a Hele-Shaw cell, starting from a carefully prepared initial state of fourteen almost identical fingers. As the flow progresses, killing off thirteen of the fingers on its way to the single-finger steady state, several systematic effects stand out, including (1) a characteristic trajectory for a finger which depends not on its position in the ‘‘starting gate’’ but rather on its final position in the ‘‘race’’ and, most importantly, (2) a cascade of reverse bifurcations, stages in which the number of competing fingers is reduced, typically by a factor of 2.

A consistent theoretical description of the global plasma modes that are excited or suppressed by the presence of a high-energy particle population is given. The present analysis underlines the importance of a finite-energetic particle response in the limit of vanishing perturbation frequency in order to stabilize resistive modes responsible for the so-called ‘‘sawtooth’’ oscillations of the central region of the plasma column.

We have observed plasma jets from laser-irradiated gold disk targets. The structures originate from low-intensity regions of the incident laser beam but propagate much faster than similar density surfaces from higher-intensity regions. The material is both cold and dense, as evidenced by its emission of soft x rays and absorption of hard x rays.

The temperature dependence of x-ray peak intensities of icosahedral AlCuFe is studied in detail. Above 670 °C, measurements of the Debye-Waller factor suggest the presence of dynamical phasons. Softening of the phason modes drives a structural transition at ∼670 °C below which the quasicrystal decomposes into coherent micrograins of a lower-symmetry phase. Implications for quasicrystal stability are discussed.

We have measured the behavior of a vibrating-wire viscometer in superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in the ${\mathrm{A}}_1$ and ${\mathrm{A}}_2$ phases in magnetic fields up to 9.2 T and at various pressures. In reduced units the viscosity in the ${\mathrm{A}}_1$ phase is, within our accuracy, independent of magnetic field and displays a minimum as a function of temperature for sufficiently high magnetic fields. Slightly below the ${\mathrm{A}}_2$ transition the viscosity shows an anomalous dip, which could indicate a new phase or a textural transformation. We offer a preliminary explanation for the observed anomalies.

The mixed cyanides, (KBr${)}_{1\mathrm{-}\mathrm{x}}$(KCN${)}_{\mathrm{x}}$, x=0.73,0.53,0.41, and (NaCn${)}_{1\mathrm{-}\mathrm{x}}$(KCN${)}_{\mathrm{x}}$, x=0.07,0.59,0.85, have been investigated by shear-torque experiments in the 0.1-Hz regime. Evidence is given that the increase of the elastic shear constant in the orientational glass state, as observed in measurements performed at finite measuring frequencies, is entirely due to relaxational effects and that correspondingly the static elastic constant is soft throughout the glass state.

We report light-scattering measurements of powder diffraction patterns of crystals of essentially hard colloidal spheres. These are consistent with structures formed by stacking close-packed planes of particles in a sequence of permitted lateral positions, A,B,C, which shows a high degree of randomness. Crystals grown slowly, while still containing many stacking faults, show a tendency towards face-centered-cubic packing: possible explanations for this observation are discussed.

We consider the effect on critical dynamics of global, rather than local conservation laws. Restricting our consideration to model B (conserved order parameter) we present theoretical arguments and numerical evidence that global conservation is sufficient to establish the universality class of model B and can be used to construct faster algorithms for the calculation of dynamical critical exponents.

We present experimental evidence of the smectic-A ($S_A$) phase in colloidal solutions of tobacco mosaic virus. The smectic-A phase is determined by the observation of a layered structure along the virus alignment direction and a liquidlike order within layers. In our samples, we also observed the characteristic $S_A$-type focal conic textures and in-layer undulational fluctuations. Our observations confirm the predictions from computer simulations and theory of smectic-A order in the system of hard rods.

New insight into the bonding of carbon monoxide with transition-metal-surfaces is provided by spin-polarized photoemission studies of CO on Fe(001). The interaction of the molecular 5σ levels with the substrate d bands is found to be very weak for both tilted and vertical CO species. The former shows clear evidence for a π-d band interaction with discrete spin-polarized features in the occupied D band; the latter shows only small changes. Inverse photoemission studies (non-spin-polarized) indicate that the unoccupied 2π level is closer to the Fermi level for the tilted CO species.

We study the surface and the reflection cluster algorithms, which have been developed for systems with global continuous symmetries by Niedermayer and Wolff, respectively, in the O(4) spin model in four dimensions. The surface algorithm appears not to be substantially better than local algorithms for this model. We show that the reflection algorithm has big advantages: It fights critical slowing down and due to the use of improved estimators it gives a variance reduction.

We study the quantization of the coset space SU(3)/U(1)×U(1), considered as an example of a compact phase space. We embed this system in the flat space $C^6$ endowed with a Poisson-bracket structure, then quantize it as a constrained system, finding consistency only for isolated symplectic structures. The space of states for each admissible symplectic structure forms an irreducible representation of SU(3). In this way, we recover in the language of constrained dynamics some of the results of the Borel-Weil-Bott theorem and geometric quantization.

In August 1988 continuous gravity measurements were made in a pumped-storage reservoir in SW Germany. Daily water-level variations of 5–22 m produced, together with the tides, a quasiperiodic gravity signal which could be measured with a resolution well below 1 μgal${=10\mathrm{}}^{\mathrm{-}8}$ m ${\mathrm{s}}^{\mathrm{-}2}$. The experiment’s goal was a search for deviations from Newton’s gravitational law, but it can also be viewed as a measurement of the gravitational constant G for effective mass distances of 40–70 m. The deviation of G from the laboratory value was found to be (0.25±0.4)% and thus is not significantly different from zero.

If a unified theory possesses non-Abelian global symmetries which are spontaneously broken it gives rise to a three-dimensional defect known as texture. In an expanding universe texture obeys a ‘‘scaling solution,’’ which produces a constant density perturbation at horizon crossing of δρ/ρ≊$m_{\mathrm{GUT}{}^2/m_{\mathrm{Planck}{}^2}}$, where $m_{\mathrm{GUT}}$ is the scale of symmetry breaking. These (isocurvature) perturbations are broadly of Harrison-Zeldovich form, but are non-Gaussian, having strong ‘‘spikes’’ in the density field. Consequences for microwave background anisotropy are briefly discussed.

All known pulsar frequencies and masses can be accounted for by plausible neutron-star models with the exception of the new fast pulsar. To withstand its rotation frequency the central density of the star must be so high that the constituents cannot be individual hadrons. If strange-quark matter (u,d,s quarks) is the absolute ground state, a star of such matter can be stable against mass loss at the frequency of the new pulsar. An essential difference between neutron stars and strange stars is the binding force, gravity for ordinary stars, and confinement and gravity in the case of strange stars.