In this paper, we suggest a new acceleration method for Abelian gauge theories based on linear transformations to variables which weight all length scales equally. We measure the autocorrelation time for the Polyakov loop and the plaquette at β=1.0 in the U(1) gauge theory in four dimensions, for the new method and for standard Metropolis updates. We find a dramatic improvement for the new method over the Metropolis method. Computing the critical exponent z for the new method remains an important open issue.

We show that string theories allow interactions potentially leading to photon and graviton-mass terms when one or more scalar fields acquire vacuum expectation values. A general analysis is presented for the case when one of these scalars is the electroweak Higgs-boson doublet. The results provide a new constraint on model building for string theories.

In the minimal supersymmetric model (MSSM), the tree-level mass of the lightest Higgs scalar ${\mathit{h}}^0$ cannot be larger than the mass of the Z boson. We have computed the one-loop radiative correction to the upper bound on ${\mathit{m}}_{\mathit{h}}^0$ as a function of the free parameters of the MSSM. We find that the dominant correction to ${\mathit{m}}_{\mathit{h}}^0$-${\mathit{m}}_{\mathit{Z}}$ is large and positive and grows like ${\mathit{m}}_{\mathit{t}}^4$, where ${\mathit{m}}_{\mathit{t}}$ is the top-quark mass. As a result, the MSSM cannot be ruled out if the CERN ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ collider LEP-200 fails to discover the Higgs boson.

The fraction f of ${\mathit{D}}^0$ semimuonic decays which occur through the Kμν mode has been measured in a hybrid emulsion spectrometer. Analysis of 124 semimuonic ${\mathit{D}}^0$-decay candidates gives f=0.32±0.05 (stat) ±0.05 (syst). From this measurement and existing data on the ${\mathit{D}}^0$ semileptonic branching ratio and lifetime, we obtain the branching ratio R(${\mathit{D}}^0$→${\mathit{K}}^{\mathrm{-}}$${\mathrm{\mu }}^{+}$ν)=(2.4±0.4±0.5)% and partial decay rate Γ(${\mathit{D}}^0$→${\mathit{K}}^{\mathrm{-}}$${\mathrm{\mu }}^{+}$ν)=(5.6±0.9±1.2)×${10}^{10}$ ${\mathrm{s}}^{\mathrm{-}1}$.

A shell-model study is made of first-forbidden β decay in A=205–212 nuclei. A least-squares fit for eighteen ΔJ=0 and 1 decays gave a scaling factor for the rank-one contributions of 0.97±0.06, i.e., agreement with experiment, and an enhancement factor ${\mathrm{\epsilon }}_{\mathrm{MEC}}$ for the rank-zero matrix element of ${\gamma }_5$ of 2.01±0.05, indicating an enhancement by 100% over the impulse approximation. A 40% effect is predicted from meson exchange. Thus, a deficiency in the meson-exchange calculation or some further unforeseen effect is suggested.

Nuclear transition rates in μ-catalyzed p-d fusion have been calculated using numerically converged ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ bound-state and p-d scattering wave functions for the first time. The transition rates for M1 radiative capture in both quartet and doublet initial states have been computed using a model of meson-exchange currents which reproduces the thermal n-d capture cross section, and are in excellent agreement with experiment. The muon internal-conversion rate is in very good agreement with a recent reanalysis of old bubble-chamber measurements. Furthermore, our nonvanishing quartet capture rate resolves the anomaly in the Wolfenstein-Gerstein effect.

By time-of-flight spectrometry we have measured the energy loss of hydrogen projectiles in helium gas. We show that for projectile velocities ${\mathit{v}}_1$ below the Bohr velocity the presence of an appreciable minimum excitation energy leads to a significant deviation of the electronic stopping cross section from the ${\mathit{v}}_1$ proportionality generally assumed; at 4 keV a dependence on roughly the third power of ${\mathit{v}}_1$ is found.

We report the first study of coherent transients excited by ultrafast pulses of THz radiation. Using a newly developed optoelectronic source of well-collimated beams of subpicosecond pulses of THz radiation to excite ${\mathrm{N}}_2$O vapor, we have observed the subsequent emission from the vapor of coherent THz pulse trains extending to as long as 1 nsec. The origin of these subpicosecond THz pulses is a periodic rephasing, during the free-induction decay, of the more than fifty coherently excited rotational lines with commensurate transition frequencies. We term this new coherent phenomenon ‘‘THz commensurate echoes.’’ The echo repetition rate is equal to the frequency spacing between adjacent lines. From the decay and reshaping of the echoes the coherent relaxation time ${\mathit{T}}_2$ and the anharmonicity factor for the ${\mathrm{N}}_2$O molecule are evaluated.

We study analytically the squeezing spectrum of second-harmonic generation in the self-pulsing regime. We prove that squeezing is still defined in the presence of a limit cycle. When the input field exceeds the self-pulsing threshold, the intensity spectrum remains smaller than the shot-noise limit in a frequency domain around the self-pulsing frequency.

An impulse approximation for ionizing collisions of clothed ions with atoms is used to explain the origin of an anomalous oscillation in the ejected electron spectrum in the region of the binary peak. In addition, measurements which evidence this feature for 1-MeV/u ${\mathrm{U}}^{21+}$ ions colliding with helium are presented. It is shown that this behavior arises from interference structures in the elastic differential cross section for the scattering of target electrons from the impinging ion and that it is associated with the well-known phenomenon of rainbow scattering.

We report the first observation of the photorefractive effect in a polymeric material, the electro-optic polymer bisphenol-A-diglycidylether 4-nitro-1,2-phenylenediamine made photoconductive by doping with the hole-transport agent diethylamino-benzaldehyde diphenylhydrazone. The gratings formed exhibit dynamic writing and erasure, strong electric-field dependence, polarization anisotropy, and estimated space-charge fields up to 26 kV/cm at an applied field of 126 kV/cm. Application of similar concepts should provide a broad new class of easily fabricated photorefractive materials.

Microwave transmission through a random mixture of aluminum and Teflon spheres at a metal filling fraction of 0.30 is found to fall initially as 1/${\mathit{L}}^2$ in agreement with predictions of the scaling theory of localization. The renormalized diffusion coefficient is determined from measurements of transmission and of the spectral intensity correlation function. This function is found to be an expansion in ${\mathrm{\delta }}^{\mathrm{-}1}$, where δ is the product of the width and density of states in the medium. From these results we find the Ioffe-Regel criterion for photons to be ${\mathit{kl}}_{\mathit{c}}$=1.6±0.4.

A new type of electron linear accelerator realized in a vacuum system, based on the ${\mathbf{V}}_{\mathit{p}}$×B acceleration scheme observed originally in plasma, has been demonstrated. The present system has a static magnetic field applied vertically to the wave propagation direction, and the particles are accelerated along the wave front at constant phase with respect to the wave. In this scheme, a greater acceleration rate than that of conventional linear accelerators has been observed. The acceleration rate is also larger than that expected from the simple theoretical model presented so far.

Electron-impact excitation rates in a capacitively coupled 13.6-MHz rf argon discharge were derived from optical emission measurements with high time and space resolution. A propagating excitation wave form is shown to exist at gas pressures as high as 1.0 Torr. The observed features—including temporal broadening of the wave form—are in agreement with recent simulation results, and can explain apparent transitions in electron energy distributions previously reported.

Analytic expressions for the reflection, transmission, and mode-conversion coefficients for electromagnetic and Langmuir waves in an unmagnetized plasma with a parabolic density profile are found for both the ‘‘direct’’ problem (incident electromagnetic wave) and the ‘‘inverse’’ problem (incident Langmuir wave). In contrast to the linear-profile problem, the absorption depends explicitly on the value of the collision frequency (cold model) or temperature (warm plasma), but a transformation of parameters relates the results for these two limits.

Coupled Alfvén waves propagating along a quadrupole magnetic field are studied. It is shown analytically that slow and fast Alfvén waves mode couple due to the spatial modulation of the quadrupole magnetic field, and one Alfvén mode can convert to another one. The process is analogous to a resonant parametric mode coupling. The coupling coefficient depends on the ellipticity of the flux surface and vanishes when the magnetic field is axisymmetric.

A plasma lens for 18-MeV round-shaped electron beams was experimentally studied; the lens is based on self-focusing due to shielding of the space charge of a particle beam by a quiescent plasma. A differential pumping technique was applied to separate the plasma chamber from the linac acceleration duct. It is shown that overdense plasmas successfully focus the electron beams. Another finding is that the plasmas appear to reduce the transverse emittance.

Deuterium neutral beams with energies up to 110 keV were injected into TFTR (Tokamak Fusion Test Reactor) plasmas at low magnetic field such that the beam injection velocities were comparable to the Alfvén velocity. Excitation of toroidal Alfvén eigenmodes was observed by Mirnov coils and beam emission spectroscopy.

Superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is interesting acoustically because it can support more than one mode of sound propagation, and these can be used to study critical properties. Recently, there has been interest in superfluid-filled aerogels, but for such compressible materials one does not observe the ordinary (fourth) sound; instead there is a mode intermediate between first and fourth sound and a second-sound-like mode. We present a theory for the modes and the first observation of the aerogel second-sound-like mode, which is important because it propagates near the critical temperature.

Using variable-cell molecular dynamics, we have studied the elastic constants of the metallic multilayer system Cu/Pd with embedded-atom potentials. Planar coherency remains intact at very low repeat distances (wavelengths), and the biaxial modulus shows decreases up to about 50%. At small repeat lengths, we predict that these coherent multilayers will become soft, in agreement with recent ultrasonic experiments, but in contrast to bulge-test observations.