The trajectory approximation is shown to explain the angular distribution of heavy raregas atoms scattered from close-packed metal surfaces, and the energy transfer for Ar on polycrystalline W. An empirical parameter, the mean energy transfer $\delta$, is extracted.

Using a simple model that describes the decrease of the amplitudes of optical structures in ion-implanted crystals, projected areas of several valence and core excitons in GaAs are determined. The last remnant of crystal-related optical structure vanishes for crystallite areas less than ${\left(16\mathrm{\AA }\right)}^2$.

Topological vacuum structures are investigated in models with spontaneous breaking of exact and approximate global symmetries. The cosmological evolution of the structure is discussed. A spontaneous breaking of an exact global U(1) symmetry gives rise to vacuum strings which can produce cosmological density fluctuations leading to galaxy formation. In a simplified axion model, the vacuum structures are strings connected by domain walls. They decay before they can dominate the universe.

Partial-wave analysis has been performed on 120 000 ${\pi }^{-}{\pi }^{-}{\pi }^{+}$ events coherently produced on nuclear targets in a ${\pi }^{-}$ beam of 40 GeV/c. Evidence has been found for a $0^{-}$ $S$ resonance at 1.24 GeV with a width $\Gamma \approx 0.36$ GeV. The data also suggest the presence of another $0^{-}$ $S$ resonance of similar width near 1.8 GeV. These observations can be interpreted as radial excitations of the $\pi$ meson.

The measurement of the nonelectromagnetic forward-backward charge asymmetry in the reaction $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$ at $\sqrt{s}\sim 34.6$ GeV and in the angular region $0<\left|cos\theta \right|<\mathrm{}0.8\mathrm{}$ is reported. With a systematic error less than 1%, we observe an asymmetry of (-8.1±2.1)%. This is in agreement with the standard electroweak theory prediction of (-7.6±0.6)%. The weak-current coupling constants are also reported.

Transverse rotation-group representation indices are shown to appear in one-loop radiative corrections. Some conjectures are made on how such index structure generalizes to higher orders. An unusual correlation between the absence of UV divergences in supersymmetric theories and the equality of such indices for fermions and bosons is described. This correlation is argued to be a fundamental indicator of higher-order UV behavior for $D=10\mathrm{}$ ($N=4\mathrm{}$) supersymmetric Yang-Mills theory and $D=11\mathrm{}$ ($N=8\mathrm{}$) supergravity. Within this context, the significance of O(8) triality is discussed.

The $\Delta B=\Delta L=2\mathrm{}$ processes hydrogen-antihydrogen oscillation and $\mathrm{pp}\to e^{+}{e}^{+} or {\mu }^{+}{\mu }^{+}$ (double proton decay) in grand unified theories are examined. Although these reactions are very suppressed in the minimal SU(5) model, their rates may be significantly increased by appending a 50-plet of Higgs scalars. In that case relatively light color sextet and doubly charged colorless scalars might mediate $\mathrm{pp}\to e^{+}{e}^{+} or {\mu }^{+}{\mu }^{+}$ at a rate observable in ongoing proton decay experiments. Consequences of this scenario are discussed.

A model is presented for diffractive charm-anticharm production in neutrino reactions, which can account for all the essential features of the like-sign dimuon data.

It is argued that the origin of the observed approximate $\left|\Delta \overrightarrow{\mathrm{I}}\right|=\frac{1}{2}$ rule is the presence of an asymptotic $\left|\Delta \overrightarrow{\mathrm{I}}\right|=\frac{1}{2}$ rule which exists among certain two-body hadronic weak matrix elements, involving especially the ground-state hadrons.

Numbers of emitted fast charged particles associated with heavier nuclear fragments are employed as a graphic means of differentiating fission and spallation contributions to target fragment emission in relativistic nuclear collisions. The violent nature of the deep spallation mechanism is observed directly.

The cascade of muonic and pionic helium atoms in targets of arbitrary density is investigated. The calculation does not use any free parameters except for strong-interaction effects. All measured x-ray intensities are reproduced, in particular the $\frac{K_{\beta }}{K_{\alpha }}$ intensity ratios in pionic helium.

It is demonstrated that the amplitude for electron-hydrogen-atom forward scattering has the third-order pole at the point $E=-13.6\mathrm{}$ eV, $E$ being the energy of the incident electron. The coefficients which characterize the pole are calculated exactly. The invalidity of the Born approximation is proved. The contribution of the pole singularity to the dispersion relation for the scattering amplitude is discussed.

A tokamak at fusion temperatures generates large amounts of synchrotron radiation. With proper configuration of the walls, this radiation can sustain the current. This is accomplished by a fish-scale wall that preferentially reflects radiation propagating in one direction while absorbing that going oppositely. The wall transfers momentum to the electrons through radiation pressure. A rough theoretical treatment shows that at high temperatures (30-50 keV) sufficient current for a steady-state tokamak may be driven.

Dispersion forces enhance the coagulation rate of small particles in a gas. Measurements of coagulation rates on ultrafine Ag and C particles with radii of 3-16 nm were performed. The results obtained with C particles almost agree with the expectations based on bulk electronic properties. However, Ag particles 14 nm in radius exhibit a very large coagulation rate. It points to an enhancement of the dispersion forces of at least a factor of ${10}^4$.

A flash desorption technique is used to show that helium atoms desorbing from a hot surface are emitted within a narrow cone about the normal direction. The emission angle and the energy of the atoms are highly correlated, which results in a "rainbow" in the desorption spectrum. These effects are discussed in terms of single-particle conservation conditions for energy and momentum transfer between phonons and atoms.

A new compact system has been developed to produce monoenergetic positrons of variable energy. The energy range available at present is between 150 eV and 28 keV, so that depth profiles can be measured. This positron beam is being used to investigate defects and defect structures close to the surface in metals and alloys. The technique of Doppler broadening of the annihilation radiation is applied for these measurements.

A functional-integral formulation is used to treat the quantum dynamics of a microscopic model of a Josephson junction, including the dissipative effects of quasiparticle tunneling. The calculation is carried to a point where it makes contact with, and therefore substantiates, recent work by Caldeira and Leggett in which the system is treated by analogy with the quantum Brownian motion of a massive particle coupled to a phenomenological heat bath.

Magnetization and magnetoresistivity measurements near 4.2 K on U${\mathrm{Al}}_2$ in fields up to 35 and 25 T, respectively, show a suppression of spin fluctuations in this material between 15 and 20 T. The experiments strongly suggest that the field and temperature effects on the paramagnon contributions are closely related. The validity of various theoretical models on the suppression of paramagnon effects are also discussed in light of these measurements.

New measurements are reported of the low-temperature resistance rise in ultrathin wires of Cu, Ni, and AuPd, which confirm the proportionality to $T^{-\frac{1}{2}}$ predicted by the interaction model. Moreover, these results and those in the literature show an absolute magnitude consistent within a factor of ∼ 2 with the predictions of this model, using independently determined parameters of similar accuracy. It is inferred that interaction effects are at least as important as localization effects in these systems.

The free-energy surface of a mean-field model for a spin-glass in a field $H$ is studied numerically. Field-cooled (FC) and zero-FC magnetizations are obtained that look qualitatively like experiment. The FC state is shown to satisfy Maxwell's relations. Changing $H$ below $T_g$ generally leads to irreversible behavior. In the absence of relaxation effects, it is found that all processes obtained upon cooling are reversible. New hysteresis effects are predicted.