A two-dimensional gauge theory which can be coupled to massless fermions is considered. All the features expected in four-dimensional Yang-Mills theory and quantum chromodynamics are found: asymptotic freedom, confinement, and dynamical mass generation. These effects (including the nonperturbative ones) are computed explicitly and exactly.

Chiral perturbation theory relates the $\left|\Delta S\right|=2\mathrm{}$ matrix element $〈{\bar{K}}^0|{\left(\bar{s}d\right)}_{V-A}\times {\left(\bar{s}d\right)}_{V-A}|K^0〉$ to the $\left|\Delta S\right|=1\mathrm{}$ matrix element $〈{\pi }^{+}{\pi }^0|{\left(\bar{s}d\right)}_{V-A}{\left(\bar{u}u\right)}_{V-A}+{\left(\bar{s}u\right)}_{V-A}\times {\left(\bar{u}d\right)}_{V-A}-{\left(\bar{s}d\right)}_{V-A}{\left(\bar{d}d\right)}_{V-A}|K^{+}〉$. The latter matrix element is measured in $K^{+}\to {\pi }^{+}{\pi }^0$ decay and the former matrix element is relevant for the predictions that the standard model makes for $\mathrm{CP}$ nonconservation in $K^0-{\bar{K}}^0$ mixing. In this paper the corrections of order $m_K^4\ln m_K^2$ to lowest-order chiral perturbation theory (i.e., order $m_K^2$) for these matrix elements are computed. The correction is large for the $\left|\Delta S\right|=2\mathrm{}$ matrix element indicating a breakdown of chiral perturbation theory.

An increase of the $e^{+}-e^{-}$ pair-creation rate above the Bethe-Heitler rate has been observed for photons incident along the $〈110〉$ axis of a Ge crystal at 100 K. The enhancement increases with increasing energy and the rate is more than doubled at 100 GeV. The observed features appear to be consistent with the theory of crystal-assisted pair creation, but the magnitude is less than predicted. Pair-creation enhancement is also observed off axis and this is attributed to coherent pair creation.

We have measured the coherent nuclear production of ${\pi }^{+}\omega$ systems at 202.5 GeV. This final state is dominated by the $B^{+}\mathrm{}\left(1235\right)\mathrm{}$ meson with a measured mass and full width of 1.271 ± 0.011 GeV and 0.232 ± 0.029 GeV, respectively. A radiative width of 230 ± 60 keV was extracted for the process $B^{+}\mathrm{}\left(1235\right)\mathrm{}\to {\pi }^{+}\gamma$.

The inclusive production cross sections and transverse momentum distributions of $K^{*0\mathrm{}}$ and ${K_S}^0$ mesons in $e^{+}{e}^{-}$ annihilation at a center-of-mass energy of 29 GeV have been measured by means of the time projection chamber detector in the PEP-4 experiment. The mean multiplicites are found to be 0.49 ± 0.04(stat.) ± 0.07(syst.) ($K^{*0\mathrm{}}+{\bar{K}}^{*0\mathrm{}}$) and 1.22 ± 0.03(stat.) ±0.15(syst.) ($K^0+{\bar{K}}^0$) per event.

We report ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}(e,e^{\prime }f)$ spectra from fission threshold to 23-MeV excitation energy for three values of momentum tranfer ($q=0.26, 0.40, \mathrm{and} 0.55$ ${\mathrm{fm}}^{-1\mathrm{}}$). The extracted strength functions for $E1\mathrm{}$ and $\frac{E2\mathrm{}}{E0\mathrm{}}$ agree well with those recently calculated with the quasiparticle random-phase approximation, except that some $E2\mathrm{}$ strength is apparently missing. $E3\mathrm{}$ and/or higher multipoles clearly contribute a significant amount of cross section throughout the excitation region.

The Enskog hard-spheres modification of the Boltzmann equation together with an appropriate mean field is used to study high-multiplicity events in relativistic heavy-ion collisions. We observe a small effect on the pion yield for the system Ar on Ar (800 MeV/nucleon) and the manifestation of collective flow for Nb+Nb (400 MeV/nucleon).

We describe measurements of the mass spectrum of charged argon clusters generated in a low-temperature free jet expansion. It contains detailed intensity variations which can be understood in terms of a simplified competing-lattice model of charged-cluster structure.

A theoretical procedure is introduced which yields eigenvalues and eigenvectors of the reactance matrix pertaining to competing dissociation and ionization processes in molecular Rydberg states. A calculation is set up in terms of adiabatic (nuclear-coordinate dependent) quantum defects $\mu \mathrm{}\left(R\right)\mathrm{}$ which contain the essence of the physics of the excited molecular complex at short range. The application to preionized and predissociated resonances in the ${\mathrm{H}}_2$ spectrum yields good agreement with experiment.

Configuration-interaction calculations of the differential high-energy electron-scattering cross sections of C${\mathrm{O}}_2$ have been performed in the first Born approximation leading to encouraging results for the total as well as the elastic and inelastic scattering, separately. A study of the potential-energy differences accessible from the cross-section curves by numerical integration points to a serious problem connected with the experimentally limited range of integration.

From the analysis of time sequences obtained from a Rayleigh-Bénard instability slightly above the transition to chaos, we derive an estimate of the fractal dimension by means of a correlation integral technique. An attempt to evaluate the Kolmogorov entropy is also presented.

We report the first observation of the emission of coherent light by an electron beam bunched at 1.06 μm by a Nd-doped yttrium aluminum garnet laser focused into an optical klystron. An enhancement of ${10}^2$ to ${10}^3$ over its spontaneous emission level at 355 nm has been observed in these experiments performed at the ACO storage ring at Orsay.

The Proto-Cleo stellarator has parameters that are sufficient to generate values of equilibrium (Pfirsch-Schlüter) currents and diffusion-driven (bootstrap) currents of magnitude large enough to permit local measurement of these currents with probes inserted in the plasma. Symmetric and antisymmetric components of the current yielded minor radial profiles that are consistent in magnitude, direction, and scaling with predicted values of Pfirsch-Schlüter and bootstrap currents.

The optical properties of single-domain chiral smectic liquid crystals have been theoretically studied as a function of the tilt angle. It is shown that structures with a particular value ${\theta }_{\mathrm{rev}}$ of the tilt angle, which depends only on the principal values of the local dielectric tensor, have very peculiar behavior. In passage through ${\theta }_{\mathrm{rev}}$ a reversal of the polarization states of the eigenfunctions and a drastic change of many optical properties occur.

We have developed a unified theory of classical fluids in the form of a hierarchy of integrodifferential equations for the free energy and direct correlation functions. This theory gives the correct $\epsilon =4-d$ expansion for critical phenomena. The presence of a hard core does not modify the Ising universality class to lowest order in $\epsilon$. The simplest approximation gives $\gamma =2\mathrm{}\nu =1.38\mathrm{}$ in $d=3\mathrm{}$. Suitable truncation of the hierarchy gives the correct lowdensity (virial coefficients) and high-density (optimized random phase) limit.

Third-sound measurements on ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixture films at 0.4 K show a stratification which disappears when the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ thickness, i.e., roughly the interface distance to the wall, is less than 4.5 atomic layers. We propose to take into account for the stratification transition the influence of the steric interaction between the film interface fluctuations, the so-called ripplons, and the substrate. This effect, considered for the first time, allows definition of a crossover length $d^{*}$ whose magnitude agrees with experimental determination.

In a general Landau-Ginzburg-Wilson Hamiltonian, symmetry allows a term linear in the gradient and trilinear in the order parameter in many cases. General renormalization-group equations to $O\left(\epsilon \right)$ are given for such terms, and applied to the antiferrodistortive phase transition in calcite ($R\bar{3}c$). The commensurate transition is continuous in mean-field theory, but in the renormalization-group theory, this new term is relevant near all fixed points to $O\left({\epsilon }^2\right)$ and causes a fluctuation-induced first-order transition.

It has been proposed that the sharp Raman lines seen in vitreous Si${\mathrm{O}}_2$ and other glasses are the signatures of highly regular rings of bonds connected into a more disordered network. We derive a condition for vibrational decoupling of the appropriate ring modes from the surrounding network, and thereby explain both the anomalously narrow linewidths and the absence of Si isotope shifts. The results encourage the development of vibrational spectroscopy as a probe of intermediate-range order in the form of regular rings in amorphous solids.

Femtosecond time-resolved dynamics of exciton screening and pairing is studied in a 53-Å GaAs multiple-quantum-well structure at 15 and 224 K. An intriguing high-energy shift of the exciton self-energy in the dense limit is reported.

By electron tunneling we have studied the superconducting properties of granular aluminum as one approaches the metal-insulator transition. We find that with increasing sample resistivity, the superconducting energy-gap edge broadens because of lifetime effects until that broadening becomes comparable to the gap. At this point, superconductivity disappears.