Enhanced radiation of up to 0.4 of the incident beam energy, measured for 4-, 15-, and 17.5-GeV positrons directed along the $〈100〉$ axis of an 80-μm-thick diamond crystal, is reported for the first time. The results are in excellent agreement with the recently proposed theory of crystal-assisted radiation based on the synchrotron formalism.

I speculate that heavy (≃ 93 GeV) pseudoscalar decays are responsible for the radiative $e^{+}{e}^{-}\gamma$, ${\mu }^{+}{\mu }^{-}\gamma$, and missing-energy + $\gamma$ events observed at the CERN $\bar{p}p$ collider. Decay signatures and the production cross section of this new particle are analyzed. For a consistent scenario, it seems that this pseudoscalar must be the partner of a "composite" $Z$ boson.

The rate of neutrinoless double beta decay between pairs of single-beta emitters is computed. The ejection of electrons with a kinetic energy higher than $Q_{\beta }$ is the experimental signature for this phenomenon. The probability of $\beta {\beta }_{0\nu }$ occurrence is proportional to the $\frac{4}{3}$ power of the volume of the radioactive source.

Experimental evidence is presented showing that collective effects may enhance the radial transport produced by an asymmetric perturbing field applied to a rotating nonneutral plasma column. The field asymmetry drives an asymmetric plasma mode and the mode field produces additional transport. Of particular interest for confinement systems is the existence of a zero-frequency plasma mode which can be driven by static field asymmetries. Applications to tandem mirrors are discussed.

We report a high-resolution synchrotron x-ray scattering study of the weakly incommensurate stripe-domain phase of stage-4 bromine-intercalated graphite. We demonstrate power-law behavior at five harmonics ($\overrightarrow{\mathrm{G}}$) of the mass density wave, and confirm the scaling of the structure factor with $G^2$. Our results are consistent with recent theories of the two-dimensional uniaxial commensurate-incommensurate transition.

Using the picosecond pump and probe technique we have detected oscillations of photoinduced transmission and reflection in thin films of $a$-${\mathrm{As}}_2$${\mathrm{Te}}_3$ and cis-polyacetylene. These oscillations are due to the generation and propagation of coherent acoustic phonons in the film. We discuss the generation and detection mechanism, and we use this effect to measure the sound velocity in a film of $a$-Si${\mathrm{O}}_2$.

The splay and bend elastic constants and the twist viscosity coefficient ${\gamma }_1$ have been measured for a series of side-chain nematic polymers. While the static properties are close to those of conventional liquid crystals, the hydrodynamic behavior resembles that of ordinary flexible polymers in the melt state. Furthermore, the results indicate an anisotropic conformation of the main chain as well as a coupling between the director rotation and the motion of the backbone.

We report results on the fractional quantum Hall effect in GaAs-${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ heterostructures at fractional Landau-level filling factor $\nu =\frac{p}{q}$ obtained with the combination of a dilution refrigerator and the National Magnet Laboratory hybrid magnet. We establish conclusively the quantiztation of the higher-order states $p$ in the series $q$. The Hall resistance is accurately quantized to 2.3 parts in ${10}^4$ for the $\frac{2}{5}$ state and 1.3 in ${10}^3$ for the $\frac{3}{5}$ state. New structures are observed near $\nu =\frac{3}{7}, \frac{4}{7}, \frac{4}{9}, \mathrm{and} \frac{5}{9}$.

By means of the Feynman path-integral method the experiment proposed by Silverman is analyzed under the classical approximation. The results give a new verification of the Aharonov-Bohm effect. It is pointed out that the multiple-valued wave functions are reasonable for describing the experiment. Furthermore, it is verified that the eigenvalues of the angular momentum of a charged, spinless particle-solenoid composite are flux dependent.

An experiment is proposed for measuring the earth's gravitomagnetic field by monitoring its effect on the plane of swing of a Foucault pendulum at the south pole ("dragging of inertial frames by earth's rotation"). With great effort a 10% experiment in a measurement time of several months might be achieved.

Compactification of twelve-dimensional space-time with geometry the product of Minkowski space-time with an eight-sphere requires a gauge group which contains Spin(8). This procedure leads to left-right asymmetric gauge couplings to fermions. A model with gauge group Spin (18) has four chiral families.

The finite-temperature excitation spectrum of the classical Toda lattice is obtained by numerical solution of the Bethe Ansatz. Bethe-Ansatz thermodynamics agrees exactly with known transfer-integral results. A soliton-phonon phenomenology is developed and its validity assessed with the Bethe-Ansatz spectrum as an exact standard. The phenomenology's intrinsic limitations become evident in a transition region, where a distinction between phonon and (nontopological) soliton is impossible.

We argue that microcanonical Monte Carlo techniques can provide direct information on the values of renormalized coupling constants in numerical renormalization-group studies. The method is tested on SU(2) lattice gauge theory with fundamental and adjoint couplings and on the two-dimensional O(3) Heisenberg model.

Because of hadronic mass shifts the $\Upsilon \mathrm{}\left(5S\right)-\Upsilon \mathrm{}\left(4S\right)\mathrm{}$ mass splitting is predicted to be 80 MeV larger than in naive potential models. The behavior of $\Delta R$ is predicted to show several bumps not corresponding to resonances.

The recently observed five single-jet events with missing $p_T>~35$ GeV can be consistently explained by gluinos ($\tilde{g}$), i.e., the supersymmetric partners of the gluons ($g$), produced via $q\bar{q}\to \tilde{g}\tilde{g}$ and $\mathrm{gg}\to \tilde{g}\tilde{g}$, with a mass in the range $15\lesssim m_{\tilde{q}}\lesssim 45$ GeV. Reducing the $p_T^{\mathrm{miss}}$ cut to the $4\sigma$ level further constrains this range to $25\lesssim m_{\tilde{g}}\lesssim 45$ GeV.

The differential cross sections of the reaction $\bar{p}p\to \bar{n}n$ were measured at 390, 490, 590, 690, and 780 MeV/c. The existence of the theoretically predicted forward dip is confirmed. The results are compared with the predictions of various $\bar{N}N$ potential models.

Phase shifts for the skyrmion breathing mode are calculated and indications of a resonance in this channel are found. We identify this resonance with the $N\left(1440\right)\mathrm{}$ and $\Delta \mathrm{}\left(1600\right)\mathrm{}$.

It has recently been shown that deep-inelastic electron scattering from nuclei at large momentum transfer can be explained if quarks move in a larger effective volume in nuclei than in free nucleons. We argue that this "partial deconfinement" may be understood as arising from the modification of symmetry-breaking dynamics as one passes from vacuum to nuclear matter.

The predictions of the $\sigma -\omega$ model for electromagnetic current are explored and found to be quite different from those given by the impulse approximation. In particular, large variations in the quasielastic electron scattering cross section are found depending upon the choice of the operator used for the current.

Collisions between two nuclei have been modeled by numerical solution of classical approximations to the equations of motion of the constituent nucleons. For the reaction Nb(400 MeV/u)+Nb, a correlated sidewards emission of nucleons is observed. This is attributed to the repulsive short-range component of the nucleon-nucleon potential. A strong dependence of the flow angle on the impact parameter is observed, in accord with recent experimental results.