Wilson-loop symmetry breaking is considered on a space-time of the form ${\mathrm{M}}_4$⊗K, where ${\mathrm{M}}_4$ is a four-dimensional space-time and K is an internal space with nontrivial and finite fundamental group. We show in a simple model that the different vacua obtained by breaking a non-Abelian gauge group by Wilson loops are separated in the space of gauge potentials by a finite-energy barrier. We then construct an interpolating gauge configuration between these vacua and show it to have minimum energy. Finally some implications of this construction are discussed.

Implications of the large $B_d^0$-B¯ ${}_d{}^0{}_{}{}^{}$ mixing measured by the ARGUS Collaboration are examined. Possible large top-quark mass is estimated. In addition, large CP-nonconservation effects in the two-body nonleptonic decays of $B_d^0$-B¯ ${}_d{}^0{}_{}{}^{}$ and $B_s^0$-B¯ ${}_s{}^0{}_{}{}^{}$ are recalculated. The results show that we still need ∼${10}^6$ $B_d$,${\mathit{s}}^0$-B¯ ${}_d{}^{}{}_{}{}^{}$,${\mathit{s}}^0$ pairs for testing these CP-nonconservation effects in the $B_d$,${\mathit{s}}^0$-B¯ ${}_d{}^{}{}_{}{}^{}$,${\mathit{s}}^0$ system.

The theory of analog pion double charge exchange on semimagic even-even nuclei is examined from the point of view of the nuclear shell model. It is shown that the amplitude for the reaction can be expressed as the sum of two independent functions for an entire shell. A more general relation is also discussed which is true for any shell in which the generalized seniority scheme is valid.

Results from a coincidence measurement of the ${}_{}{}^{16}{}_{}{}^{}$O(${\pi }^{+}$,${\pi }^{+}$${\pi }^{\mathrm{-}}$) &=280 MeV are reported, the first of this class. The energy- and angular-integrated cross section was found to be 2950±450 μb and is compared with theoretical predictions. Low-energy positive-pion intensities are found to be much higher than those yielded by a four-body phase-space calculation.

In the local-density and semiclassical approximation, a relativistic Vlasov equation is constructed from the Walecka model. Applying it to heavy-ion collisions at intermediate energies, we obtain results that are similar to those from the more complicated time-dependent Dirac equation. Compared with the results from the nonrelativistic Skyrme interaction, the relativistic effect is evident in the enhanced transverse-momentum distribution during the collision.

Laser-polarized lithium vapor with density ${10}^{14}$ ${\mathrm{cm}}^{\mathrm{-}2}$ in a differentially pumped cell was developed and used as a target in the nuclear fusion reaction ${}_{}{}^6{}_{}{}^{}(\mathit{\alpha }$,γ${)\mathrm{}}^{10}$B. A large change (25%) in reaction cross section relative to an unpolarized target was observed.

Above-threshold ionization (ATI) is investigated in xenon with pulses of light at 616 nm ranging from 15 to 0.4 psec. Significant energy shifts and broadenings of the ATI peaks are observed. For pulse widths less than 1 psec, the individual ATI peaks break up into a narrow fine structure, apparently due to resonance enhancements in the ionization process produced by ponderomotive shifts of states.

We report the first systematic study of the field ionization threshold of molecular Rydberg states. We find that the v=0 np series of both ortho and para ${\mathrm{H}}_2$, converging to the lowest rotational state of ${\mathrm{H}}_2$${\mathrm{}}^{+}$ with n ranging from 18–30, ionize at fields given by 1/16${\mathrm{n}}_{\mathrm{s}}^4$ with ${\mathrm{n}}_{\mathrm{s}}$, the effective quantum number at the field at which ionization takes place given by ${\mathrm{n}}_{\mathrm{s}}$=n-0.5. Our threshold field measurements suggest that the ionization process is described classically.

The Lyapunov dimension of an incompressible, homogeneous, two-dimensional periodic shear flow with moderate resolution (from ${16}^{\mathrm{*}}$16 up to ${128}^{\mathrm{*}}$128 points) is calculated. The results show that the dimension of the chaotic attractor is much lower than the total number of degrees of freedom represented in the numerical system, and depends essentially on the scale at which energy is injected in the system, and not (or very weakly) on the Reynolds number, suggesting that only a fraction of the modes at a scale larger than that of the forced mode is turbulent.

We investigate the instability of curvature radiation of a relativistic beam of charged particles in a very strong curved magnetic field, which is of interest as a pulsar radiation mechanism. The conditions for growth are a fairly steep boundary at the outer edge of the beam and high frequencies meeting a non-WKB requirement. High growth rates are found.

A general method is described for the calculation of interatomic potentials in condensed-matter systems by use of a maximum-entropy Ansatz for the interatomic correlation functions. The interatomic potentials are given explicitly in terms of statistical correlation functions involving the potential energy and the structure factor of a ‘‘reference medium.’’ Illustrations are given for Al-Cu alloys and a model transition metal.

We have carried out the first electron-diffraction study of thin free-standing liquid-crystal films. Stable films were maintained in a finite atmosphere with use of a differentially pumped sample chamber. It is possible to observe the behavior of single domains even in thin hexatic films by limiting the sample area probed to several micrometers squared. Initial results on two systems exhibiting tilted hexatic behavior have provided novel information about the bond-orientational order parameters and their scaling relationship in films of a few molecular layers.

We show that long-range positional order in the sense that the density Fourier transform is a set of δ functions is not essential for the phenomenon of facet formation. Facets can occur in certain classes of perfect bond-oriented systems which lack the conventional long-range positional order, allowing the appearance of widths in the diffraction peaks. The predicted facets in some of these systems are consistent with the recently observed triacontahedral grain shapes in ${\mathrm{Al}}_6$${\mathrm{LiCu}}_3$ and dodecahedral grain shapes in Al-Mn-Si, as well as the strong spatial disorder as indicated by the x-ray diffraction measurements.

Infrared-absorption measurements have been performed on the fundamental band of physisorbed ${\mathrm{H}}_2$. Distinct vibrational, rotational, and adsorbate phonon features induced by surface and intermolecular interactions are identified. When compared with adsorption isotherms the surface-enhanced vibrational line saturates at 40% of the surface layer coverage which results from the short range of the surface-induced dipole in Steele’s bilayer model and is inconsistent with a high-density monolayer phase. Our results also strongly point to the formation of islands at low coverages.

Order-disorder critical behavior of the adsorption system O/Ru(0001) at (1/4 monolayer, ordered in a p(2×2) structure, is studied by use of LEED. By measuring the profiles—and the peak and integrated intensities—of the (1/2-order oxygen LEED spots as function of temperature for 0.004<‖(T-${\mathrm{T}}_{\mathrm{c}}$)/${\mathrm{T}}_{\mathrm{c}}$‖<0.2, we determine the critical exponents α, β, γ, and ν independently. They agree to within 3% to 10% of the theoretical values for the two-dimensional four-state Potts model universality class.

Measurements of the self-diffusion coefficient in supercooled water to 300 MPa are reported. Translational diffusion in liquid water at 243 K is enhanced by 60% when the pressure is increased from 0.1 to 150 MPa, and rotational diffusion is enhanced by almost 250% between 0.1 and 250 MPa. These striking anomalies are interpreted in terms of the proximity of a conjectured line of spinodallike stability limits in the supercooled liquid.

X-ray diffraction and electrical conductivity measurements demonstrate that CsI undergoes pressure-induced, high-temperature decomposition to its constituent elements at pressures exceeding 45 GPa. Our results provide a natural explanation for the apparent discrepancy between previous shock-wave and static compression measurements performed on CsI. Also, our observations imply that the metallic phase of CsI is metastable and that changes in the electronic properties of the heavy alkali metals at high pressures strongly decrease the tendency of these elements to form ionic compounds.

Silicon dioxide is fundamental in geology, in the electronic materials industry, and in the glass industry. We have carried out an ab initio total energy minimization study of the structure and bonding of alpha cristobalite using nonlocal pseudopotentials in a Car-Parrinello–type molecular dynamical method. The electronic energy is expressed in the local-density approximation. The use of a separable nonlocal pseudopotential preserves the O(M lnM) scaling of the computation for M plane waves. The resulting theoretically computed minimum energy structure agrees well with experiment.

The electronic structure of interacting, few-electron systems confined in quasi-zero-dimensional, ultrasmall, quantum-well boxes has been calculated by use of the multielectron effective-mass Schrödinger equation. The configuration interaction method is used to include electron correlation. Correlation effects are dominant in large boxes; the electrons form a Wigner lattice. In smaller boxes subband spacing becomes dominant and the carriers become frozen in the lowest subbands. The calculations determine how and on what size scale this transition occurs.

We report time-of-flight experiments in the time range from 0.2 psec to 1.8 nsec in a-Si:H–a-${\mathrm{SiN}}_{\mathrm{x}}$:H multilayer structures using a purely optical technique. The transport mechanism of photoexcited carriers is shown to be dispersive and its characteristic parameters are determined in the temperature range 70–300 K.