We show that recent data from the CERN ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ collider LEP on the Z line shape and decays give stringent new constraints on mixing of e and τ with exotics and Z-Z’ mixing. Even in nonstandard models, where both the visible and the invisible part of the Z width are modified, a fourth light neutrino is unlikely unless substantial mixings between neutrinos and exotics are allowed. If the gluino is detectable at the Fermilab Tevatron then the lighter-chargino mass is tightly constrained (>42 GeV).

Assuming the reactions ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$→uu¯,dd¯ to produce final states consisting of pions only, we consider effects that are sensitive to the coherence of the uū and dd¯ systems. The ratio of odd- and even-multiplicity final states varies from 1/9 at low energies to 3.5 on the ${\mathit{Z}}^0$. For left-handed electrons, this ratio is as high as 400 in the region around √s =75 GeV. There is a ${\mathrm{\pi }}^{+}$-${\mathrm{\pi }}^{\mathrm{-}}$ asymmetry (22% on the ${\mathit{Z}}^0$) for odd-multiplicity configurations, but none for even multiplicity. These features are absent in models in which the uū and dd¯ systems fragment independently.

We describe a search for the decay of the Z boson into pairs of doubly charged Higgs bosons with the Mark II detector operating at the SLAC Linear Collider. Each Higgs boson is assumed to decay into a same-sign leptonic pair. No event candidates are found in a sample of 528 Z decays. At the 95% confidence level, this result excludes the region of leptonic coupling ${\mathit{g}}_{\mathit{l}\mathit{l}}$>3×${10}^{\mathrm{-}7}$ and Higgs-boson mass 6.5<${\mathit{M}}_{\mathit{H}}$<36.5 GeV/${\mathit{c}}^2$ for isotriplet (left-handed) Higgs bosons. Isosinglet (right-handed) Higgs bosons are excluded in the same ${\mathit{g}}_{\mathit{l}\mathit{l}}$ interval and in the mass interval 7.3<${\mathit{M}}_{\mathit{H}}$<34.3 GeV/${\mathit{c}}^2$.

Using the Mark II detector at the SLAC Linear Collider, we search for decays of the Z boson to a pair of nonminimal Higgs bosons (Z→${\mathit{H}}_{\mathit{s}}^0$${\mathit{H}}_{\mathit{p}}^0$), where one of them is relatively light (≲10 GeV). We find no evidence for these decays and we obtain limits on the ${\mathit{ZH}}_{\mathit{s}}^0$${\mathit{H}}_{\mathit{p}}^0$ coupling as a function of the Higgs-boson masses.

We have searched for the decay ${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathit{e}}^{+}$${\nu }_{\mathit{e}}$ in data from the Fermilab charm photoproduction experiment E691. The resulting upper limit is B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathit{e}}^{+}$${\nu }_{\mathit{e}}$)<0.45B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$). Since the branching fraction for ${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathit{e}}^{+}$${\nu }_{\mathit{e}}$ can be calculated from the measured branching fraction B(${\mathit{D}}^{+}$→K¯ ${}_{}{}^{\mathrm{*}0}{}_{}{}^{}$${\mathit{e}}^{+}$${\nu }_{\mathit{e}}$) to be (1.7±0.3)%, this implies a 90%-confidence-level lower limit on B(${\mathit{D}}_{\mathit{s}}^{+}$→φ${\mathrm{\pi }}^{+}$) of 3.4%.

Ab initio R-matrix scattering calculations are presented for electron-${\mathrm{H}}_2$ collisions for energies up to 30 eV. Excitation from the ground state, ${\mathit{X}}^1$${\mathrm{\Sigma }}_{\mathit{g}}^{+}$, to five accurately represented, low-lying electronic states, ${\mathit{b}}^3$${\mathrm{\Sigma }}_{\mathit{u}}^{+}$, ${\mathit{a}}^3$${\mathrm{\Sigma }}_{\mathit{g}}^{+}$, ${\mathit{B}}^1$${\mathrm{\Sigma }}_{\mathit{u}}^{+}$, ${\mathit{c}}^3$${\mathrm{\Pi }}_{\mathit{u}}$, and ${\mathit{C}}^1$${\mathrm{\Pi }}_{\mathit{u}}$, is explicitly considered. An attempt is made to rationalize the wealth of experimental data. Resonance structures similar to those assigned experimentally to the a and c series are found as well as a number of other resonancelike features.

Unimolecular dissociation channels of mass-selected doubly charged sodium clusters ${\mathrm{Na}}_{\mathit{n}}^{++}$ have been determined for cluster sizes near and above the critical size, ${\mathit{n}}_{\mathit{c}}$=27, from which doubly charged clusters are detectable in mass spectra. On a time scale of 50 μs with respect to ionization, doubly charged clusters of size n=${\mathit{n}}_{\mathit{c}}$ are found to fission asymmetrically. For cluster sizes above ${\mathit{n}}_{\mathit{c}}$, however, evaporation of a neutral monomer is the dominant channel for delayed dissociation. An estimation of the height of the Coulombic barrier is given for ${\mathrm{Na}}_{\mathit{n}}^{++}$ near the critical size, using the framework of statistical theory.

We report the observation of high-intensity sub-Poissonian light using the correlated ‘‘twin’’ beams generated by an optical parametric oscillator. The intensity fluctuations in one of these beams are reduced by a feedforward correction mechanism that monitors the intensity of the second beam. The observed reduction in noise power is up to 24% below the shot-noise limit.

The first successful laser cooling of ions at relativistic energies was observed at the Heidelberg TSR storage ring. A ${}_{}{}^7{}_{}{}^{}\mathrm{Li}_{}^{+}{}_{}{}^{}$-ion beam of 13.3 MeV was oberlapped with resonant copropagating and counterpropagating laser beams. The metastable ions were cooled from 260 K to a longitudinal temperature of below 3 K and decelerated by several keV. The longitudinal velocity distribution was determined by a fluorescence method. After laser cooling a strongly enhanced narrow peak appeared in the Schottky noise spectrum in addition to the uncooled ion distribution.

The modification of the statistical properties of the vacuum fluctuations, via quadrature squeezing, can dramatically change the mechanical manifestations of light on atoms moving in a standing laser wave. This phenomenon can be attributed to the altered decay rates of the atomic dipole in squeezed vacuum.

Axial and circular birefringence effects are introduced which conserve parity and time-reversal invariance, and which are induced by time-varying electric fields and electromagnetic fields. In each case the symmetry of the complete experiment is considered, and equations for the birefringence are given in terms of molecular-property tensors of the ensemble.

We consider a ‘‘sticky gas’’ in which collisions between spherical particles are perfectly inelastic. Thus the two colliding particles conserve mass and momentum, but merge to form a single more massive sphere. A scaling argument suggests that the average mass of a particle grows as ${\mathit{t}}^{2\mathit{D}/(2+\mathit{D})}$, where D is the spatial dimension. In the case D=1 this result is confirmed by numerical simulation.

For a sequence of solvable solid-on-solid models, an exact analysis of the faceting transition is performed. It is shown that the curvature of the equilibrium crystal shape jumps at the roughening temperature with an amplitude given by an integer (≥1) multiple of the universal value predicted by Jayaprakash, Saam, and Teitel. An interpretation of this phenomenon, universal quantization of curvature jump, s presented from the viewpoint of the non-Abelian bosonization theory.

Using neutron-spin-echo and time-of-flight spectroscopy we have investigated the precise temperature dependence of the elastic (nonergodic) fraction in the spectrum of density fluctuations of the glass-forming polymer polybutadiene. With increasing temperature we found a critical decrease of the normalized elastic intensity following closely the (${\mathit{T}}_{\mathit{c}}$-T${)}^{1/2}$ behavior predicted by the mode-coupling theory. The critical temperature was determined to be ${\mathit{T}}_{\mathit{c}}$=216±1 K, i.e., 35 K above ${\mathit{T}}_{\mathit{g}}$.

X-ray diffraction is used to study the phase behavior and structure of the Au(001) surface between 300 K and the triple point. For T>1170 K, the x-ray reflectivity is consistent with a thin, disordered surface film. At 1170 K, there is a reversible transition to an incommensurate, hexagonal overlayer on top of the square substrate. At 970 K, the orientation of the hexagonal layer rotates discontinuously by 0.81° with no observable change in incommensurability.

The atomic structure of ordered Cu adsorbate layers on Au(111) and Au(100) electrode surfaces and of the clean substrates was resolved in scanning tunneling microscopy images taken in situ. For submonolayer coverages deposited from sulfuric acid solutions under potential control, various ordered structures were observed. The quasihexagonal arrangement of Cu atoms in these structures reflects increasingly repulsive interactions between closely spaced Cu adatoms. These structures differ from the pseudomorphic Cu adlayer formed under vacuum conditions, which demonstrates the structure-determining role of the coadsorbed anions.

Excess electrons attached to small alkali halide clusters give rise to optical-absorption bands whose characteristics are highly specific to the mode of electron localization. Optical spectra measured by cluster beam and resonant two-photon ionization spectroscopy agree well with predictions of coupled classical-quantum simulations, and are interpreted in terms of two localization modes: surface F-center and diffuse surface states.

We consider the free energy, averaged over disorder using the replica method, of an Ising spin glass on a d-dimensional hypercubic lattice. We demonstrate that the free energy can be expanded in powers of 1/d, and that the zeroth-order (d=∞) result recovers thermodynamics identical to that of the Sherrington-Kirpatrick model. We explicitly solve the model near (and below) its spin-glass critical temperature to order 1/${\mathit{d}}^2$, and find an enhancement of replica-symmetry-breaking effects as the dimension is decreased.

In disordered superconducting Cu-Zr alloys with dilute magnetic impurities, we have observed a new type of resistance anomaly which gives rise to strongly increased scattering of conduction electrons in a narrow temperature range above ${\mathit{T}}_{\mathit{c}}$ and appears to be due to interaction between superconducting fluctuations and spin. For a given level of impurities this phenomenon is peaked around ${\mathrm{Cu}}_{50}$${\mathrm{Zr}}_{50}$, but is observable from 36 to 60 at.% Zr. When the Cr impurity concentration is varied in ${\mathrm{Cu}}_{50}$${\mathrm{Zr}}_{50}$, a resistance peak can be observed for 100–600 ppm Cr with a maximum peak height of about 6% of the measured resistance. The effect is destroyed by a magnetic field of some tenths of a tesla.

We have made the first direct measurement of the quantum susceptance which arises from the nondissipative part of the quasiparticle tunneling in a superconductor-insulator-superconductor (SIS) junction. The resonant frequency of a resonator which contains an SIS junction depends on the dc bias due to the bias dependence of the quantum susceptance. The observed 19% shift of the resonant frequency, form 73 to 87 GHz, is in excellent agreement with the Werthamer-Tucker theory. This quantum susceptance should exist in other devices such as quantum-well structures.