This paper discusses a first-order SU(3) theorem relating the weak and electromagnetic form factors of the pseudoscalar mesons with an error of second order in the symmetry breaking. Recent measurements of the $K^0$, $K^{-}$, and ${\pi }^{-}$ mean square charge radii open the possibility of testing a prediction of this theorem in the near future.

Existing data from deep underground experiments are analyzed to deduce the total lifetime of the nucleon to be ≳ ${10}^{30}$ yr (at 90% confidence level) considering decay modes given by currently popular grand unified theories. Limits on partial rates of some of the important decay modes are also given.

We have measured the differential cross sections of the ($p$,$n$) reaction on ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ to the ground state of the final nucleus ($\Delta J=1\mathrm{}$, $\Delta I=1\mathrm{}$, $\Delta P=0\mathrm{}$) at $E_p=144\mathrm{}$ MeV and $0°<{\theta }_{\mathrm{lab}}<20\mathrm{}°$. We treat the nuclei as elementary particles, extract the initial-nucleus-pion-final-nucleus coupling constants, and compare them with predictions based on the partial conservation of axial-vector current hypothesis. The calculations, which have no free parameters, agree with the data for ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, but not for ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$.

The filamentation instability of the electron and positron colliding beams in a storage ring is investigated within the framework of the Vlasov-Maxwell equations, and a closed algebraic dispersion relation for the complex eigenfrequency $\omega$ is obtained. It is shown that the typical growth rate of instability is a substantial fraction of the electron plasma frequency ${\omega }_{\mathrm{pe}}$. For parameters characterizing the recent colliding-beam experiments at DESY, the instability threshold is marginally satisfied.

Angular distributions of various Mg, Sc, Cu, Ag, and Ba nuclides produced in the interaction of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ with 400-GeV protons have been measured. While all the angular distributions peak at ∼ 90°, those obtained for certain products are characterized by greater backward than forward emission in the laboratory system. This category includes both neutron-deficient and neutron-excess Sc fragments as well as neutron-deficient Cu and Ag nuclides.

Exact calculations of the photoionization cross sections of ground-state H in the presence of an external electric field are presented. The oscillations obtained above the zero-field ionization limit for $\pi$ polarization do not arise from specific properties of $m=0\mathrm{}$ states, but from cancellation effects in the oscillator strengths due to the symmetry properties of the wave functions and of the light. The dependence of the cross section upon the light polarization is thoroughly explained and agrees with recent experiments on Rb.

We consider the effect of light reflected from the plasma critical surface on stimulated Brillouin scattering. For an expanding plasma, there will be a certain Mach number where the reflected light acts as a noise source for stimulated—Brillouin-scattering exponentiation. We show calculations and plasma simulations that exhibit significantly enhanced levels of scattering.

This Letter analyzes peaks in ultraviolet photoemission spectra due to the $5p_{\frac{3}{2}}$ and $5p_{\frac{1}{2}}$ levels of Xe atoms adsorbed on various surfaces. The binding-energy shifts are used to distinguish between (a) Pd- and Pt-like adsorption sites on Pd-Pt surfaces, (b) the 5×1 and 1×1 modification of an Ir(100) surface, and (c) step sites and terrace sites on a stepped Ru(0001) surface. The findings are ascribed to local work-function effects and to initial- and final-state orbital energy effects. Xe atoms are thus a very sensitive, local, surface probe.

The temperature dependence of the shear modulus $\mu$ in the two-dimensional electron solid has been determined in a computer simulation. It is found that at low temperatures $T$, $\mu$ decreases linearly with increasing $T$. A sharp drop of $\mu$ together with the onset of electron diffusion in the range $140>\mathrm{}\Gamma >120\mathrm{}$, where $\Gamma =\frac{e^2{\left(\pi n_s\right)}^{\frac{1}{2}}}{k_{\mathrm{B}}T}$, suggestes a melting point consistent with the experiment by Grimes and Adams. The results presented here are consistent with recent theories of dislocation-mediated melting in two dimensions.

Low-energy electron diffraction observations of carefully cleaned and annealed Cr(100) surfaces show a sharp and intense $(\sqrt{2}\times \sqrt{2})R45\mathrm{}°$ structure. Auger-electron spectroscopy measurements indicate that this "anomalous" structure is actually a clean-surface effect. A strong contamination-sensitive feature is revealed by angle-resolved photoemission and it is suggested that reconstruction results from an instability connected with a peak near $E_{\mathrm{F}}$ in the surface density of states of the Cr(100) (1×1) surface.

The resonant mixing of forward-propagating phonons with a microwave electric field in indium-doped silicon leads to the generation of backward-propagating phonons. The magnetic-field-frequency dependence of the backward-wave generation gives rise to a spectroscopic tool for the study of deep states in semiconductors, which partially overcomes the effects of inhomogeneoous broadening.

The possibility of Bose condensation into the lowest-energy, extended, Hartree-Fock eigenstate in the presence of a random potential is studied. Using the existing folklore about Anderson localization, and adding interactions, we find that the fluctuations are logarithmically divergent and that stable broken symmetry is impossible for $n>~2$.

We demonstrate here that nonlinear mixing of four surface-plasmon waves can be used to probe the Raman resonances of liquids. The results are in good agreement with theoretical prediction. The technique should be useful for surface studies.

The existence of a new phase boundary for thin-film superconductors in an applied magnetic field and in rotating films of superfluid helium is predicted. The melting temperature is shown to lie below and scale with the zero-field vortex plasma transition temperature.

Enhancement of photoionization cross sections due to spatially varying photon fields at a metal surface has been observed in the normal-emission cross sections for the surface state and Fermi level of A1(100) at photon energies between 9 eV and 23 eV. The data for Fermi-level photoexcitation are in excellent agreement with theoretical results for jellium. Below $\hslash {\omega }_p$, the predominant contribution to the photoionization matrix element comes from the spatially varying fields, which provide the momentum required for photoexcitation.

This Letter analyzes the electron states associated with the silicon vacancy and proposes a distortion model for the surrounding atoms that is derived from self-consistent calculations for single-particle states and from model calculations of elastic restoring forces. The predicted level structure is such that $V^{+}$ is, contrary to currently accepted ideas, a metastable state which decays either to $V^0$ or to $V^{++}$, depending on the Fermi energy.

A neutron diffraction experiment on a random mixture of two antiferromagnets with competing spin anisotropies, Fe${\mathrm{Cl}}_2$·2${\mathrm{H}}_2$O and Co${\mathrm{Cl}}_2$·2${\mathrm{H}}_2$O, clearly demonstrates a decoupling of the spin components near the tetracritical point which occurs in the concentration versus transition temperature phase diagram. It is shown that the new phase observed in the intermediate concentration region is the "mixed ordering" phase (or equivalently the "oblique antiferromagnetic" phase).

This paper reports the first experimental observation of "slow" pulse propagation in the exciton-polariton resonance of a direct-gap semiconductor. The propagation delay of short light pulses transmitted through a 3.7-μm-thick GaAs crystal was measured directly with a cross-correlation technique. Polariton group velocities from $\frac{c_{\mathrm{vac}}}{3.6}$ down to $\frac{c_{\mathrm{vac}}}{2000}$ were found when the wave-packet center frequency was tuned through the $n=1\mathrm{}$ exciton resonance.

The measured spin polarization of the photoelectrons emitted from Ni(111) shows a crossover from negative to positive values at 270±90 meV above photothreshold. This is in constrast to the case of Ni(100), where a crossover at about 75 meV occurs. A single-particle photoemission calculation with an exchange splitting of 0.33 eV, and which does not invoke emission from surface states, is in good agreement with the experimental results for both faces. These new results corroborate the empirical band structure obtained by Eastman and co-workers from angle-resolved photoemission data.

By use of ${\mathrm{Ni}}_{1-x}{\mathrm{Cu}}_x$ alloys to vary the ferromagnetic Curie temperature, the activation energy for Ni${\mathrm{}\left(\mathrm{CO}\right)\mathrm{}}_4$ formation is found to be greater when the metallic substrate is ferromagnetic than when it is paramagnetic. This difference in activation energy is approximately the bulk exchange energy of the substrate and depends on the bulk Ni concentration. On the basis of the experimental results, a model for associating the change in activation energy at $T_{\mathrm{C}}$ with rupture of the metallic bond is presented.