We study an effective local interaction as a possible source of hard photons in the decay $Z_0\to \overline{\mathrm{ll}}\gamma$. We restrict the form of this interaction by the requirements that it be SU(2) ⊗ U(1) gauge invariant, $\mathrm{CP}$ invariant, and chirality conserving. Including constraints derived from the agreement of the standard model in other neutral current experiments, we find that the ratio of radiative to nonradiative leptonic decay widths is given by $0.6{\left(\frac{M_Z}{M_{\Lambda }}\right)}^4$ where $M_{\Lambda }$ is the mass scale characterizing the "new physics." This ratio is less than the preliminary experimental indication of approximately 10% if $M_{\Lambda }$ is greater than 150 GeV.

We extend the theory of pion scattering to study charge-exchange reactions from oriented, deformed nuclei. We show that measurement of the orientation asymmetry for pion charge exchange can lead to a determination of the deformation, ${\beta }_2^N$, of the excess neutron distribution.

A cascade model has been applied to a global analysis of high-multiplicity events in 400-MeV/nucleon Ca+Ca and Nb+Nb collisions. The global analysis gives a sideward peak in the angular distribution of the high-multiplicity Nb+Nb events. The appearance of the peak is closely related to the development of cascade collisions from the participant region into the remaining (cold) region of the nuclei, which induces the recoil motion of these nuclei, i.e., the bounceoff effect.

Fragments with atomic numbers covering the entire range of the mass-asymmetry coordinate ($Z=1\mathrm{}$ to $Z=\frac{Z_{\mathrm{CN}}}{2}$) were observed from the decay of compound nuclei (CN) produced in reactions of 7.4- and 8.4-MeV/nucleon ${}_{}{}^{74}{}_{}{}^{}\mathrm{Ge}$, ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$, and ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ with ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. The evolution of the charge distribution with increasing mass of the compound nucleus ($A=83\mathrm{} \mathrm{to} 151$) reflects the topological change in the potential-energy surface associated with crossing the Businaro-Gallone point.

The observation of large, forward-peaked cross sections in low-energy pion-nucleus double-charge-exchange reactions could provide evidence that six-quark, hidden-color components of nuclear wave functions exist.

Pion and proton production are measured to investigate thermal equilibrium in central collisions of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$+KCl at 1.8 GeV/nucleon. The bulk of the pion yield is isotropic in the c.m. system, with an apparent temperature of 58±3 MeV, much lower than the 118±2 MeV of the protons. It is shown that the low pion "temperature" can be explained by the decay kinematics of delta resonances in thermal equilibrium. A (5±1)% component in the pion spectrum is, however, found to have a temperature of 110±10 MeV. The effect on the spectra of possible contributions from collective radial flow is discussed.

A simple model proposed by Baylis for treating the interaction of excited and ground-state alkali-metal atoms with multiple rare-gas perturbers has been applied to the calculation of peak wavelengths in the band emission of $\mathrm{K}\mathrm{}\left(5s\right)\mathrm{}{\mathrm{Xe}}_N$ exciplexes observed by Yabuzaki et al. In addition, the binding energies of these exciplexes have been calculated and compared with experiment.

The quantum-mechanical master equation of a homogeneously broadened single-mode laser is solved in the regime of the Lorenz strange attractor. The quantum Wigner distribution is obtained, replacing the classical invariant measure on the attractor, and reducing to it in the classical limit.

We show that it is possible to guide a relativistic electron beam into the center of a modified betatron accelerator by judiciously creating a plasma channel with a laser. A slight variation of this scheme can be used to extract the beam after the acceleration phase.

Simultaneous measurement of the conductivity and the elasticity exponents in two dimensions for a percolating system made of metal and voids is reported. The elasticity exponent is $T=3.5\mathrm{}\pm 0.4$, much larger than the conductivity exponent $t=1.2\mathrm{}\pm 0.1$. This result is in excellent agreement with the theoretical prediction of Bergman.

Energy spectra of the products of surface scattering of ${\mathrm{H}}_2^{+}$ and ${\mathrm{N}}_2^{+}$ in the primary-beam energy range from 200 to 600 eV are presented. Large neutral-molecular yields are observed for incident ${\mathrm{N}}_2^{+}$, i.e., beams of neutral molecules can be produced with optical properties similar to that of the incident beam. The results provide a new experimental method to study resonant and Auger-type processes in ion-surface charge-exchange events.

By means of phonon spectroscopy with superconducting-Al tunnel junctions as tunable phonon generators we show that the threshold energy of the phonon-induced conductivity for Si: ${\mathrm{B}}^{+}$ and Si: ${\mathrm{P}}^{-}$ agrees well with far-infrared data, proving that the ionization is mainly a one-phonon process. This ionization mechanism allows a sensitive detection of very-high-frequency phonons.

We report a synchrotron-radiation study of angle-resolved photoemission from single crystals of the random alloy Cu-40%-Ni, combined with first-principles Korringa-Kohn-Rostoker coherent-potential-approximation photocurrent calculations. We find that the intensity of emission from the Ni $d$ states, relative to that from the Cu $d$ states, reveals the $\overrightarrow{\mathrm{k}}$ and energy dependence of the disorder broadening of the electron states. Our results indicate that the surface composition profile is monotonic and not, as previously reported, oscillatory.

Numerical studies of variable-range hopping in finite one-dimensional systems show large variations in the resistance as a function of chemical potential. This may explain recently observed structures in resistance versus gate voltage in narrow metal-oxide-semiconductor field-effect transistors. Our explanation suggests the possibility of probing a particular pair of localized states.

Ultrathin films of Sn have been grown incrementally on substrates held at 15 K and then studied in situ at low temperatures. This process of repeatedly increasing the thickness of a film facilitates the investigation of thickness-dependent physical properties. The superconducting transition temperature has been found to oscillate with a period which was nominally about 4 Å. The latter is approximately a factor of 2 larger than the prediction of simple theoretical models. Oscillations of the normal-state resistance with thickness have not been observed.

High-resolution (0.13 eV) photoemission measurements performed at low temperatures (≈ 20 K) show that a sharp feature (measured width ≃ 0.15 eV at full width at half maximum) exists at the Fermi edge in the electronic structures of U${\mathrm{Be}}_{13}$ and U${\mathrm{Pt}}_3$. In U${\mathrm{Be}}_{13}$ the feature shows some temperature dependence.

The spectral momentum density of the valence band of an amorphous carbon film has been measured by ($e$, $2e$) spectroscopy. Two "bands," energy as a function of momentum, are resolved. One extends from 23 eV below the Fermi energy to about 10 eV below $E_{\mathrm{F}}$. The other, ∼ 9 eV below $E_{\mathrm{F}}$, does not disperse significantly. Although the existence of diamond bonding in the film cannot be ruled out, the bands are more suggestive of the graphite band structure.

Results from the solution of the inverse-scattering problem in three dimensions are used to obtain representations of the potential and of the zero-energy wave function in terms of the scattering amplitude, the bound states, and the positive-energy wave functions. Some simple consequences are derived.

The linear stability analysis for solitary waves is revisited. It is shown that the generally ignored defective degeneracy of the Goldstone mode is associated with a perturbation with algebraic time dependence generating a solitary wave moving with infinitesimally changed velocity. If damping is switched on, the defective degeneracy of the Goldstone mode is lifted by the occurrence of a universal relaxation mode. Similarly, soft-instability modes of solitary waves are also defectively degenerate and thus accompanied by an algebraic mode.

The Einstein quadrupole formula, in the version "news function equals third time derivative of transverse quadrupole moment," is established for a specific quasi-Newtonian system by a method based upon curved-space null cones.