We present the one-loop helicity amplitudes with five external gluons. The computation employs string-based methods, new techniques for performing tensor integrals, and improvements in the spinor helicity method.

Using a sample of 935 000 BB¯ pairs collected with the CLEO-II detector at the Cornell Electron Storage Ring, we have obtained upper limits on the branching ratios for the b→${\mathit{ul}}^{\mathrm{-}}$ν¯ processes ${\mathit{B}}^{\mathrm{-}}$→ω${\mathit{l}}^{\mathrm{-}}$ν¯, ${\mathit{B}}^{\mathrm{-}}$→${\mathrm{\rho }}^0$${\mathit{l}}^{\mathrm{-}}$ν¯, and B${\mathrm{¯}}^0$→${\mathrm{\rho }}^{+}$${\mathit{l}}^{\mathrm{-}}$ν¯. The combined result using the relationships among the widths for these three modes is B(${\mathit{B}}^{\mathrm{-}}$→${\mathrm{\rho }}^0$${\mathit{l}}^{\mathrm{-}}$ν¯)<(1.6–2.7)×${10}^{\mathrm{-}4}$ at 90% C.L., where the range of values is due to model dependence of the detection efficiencies. These measurements yield the limits ‖${\mathit{V}}_{\mathit{u}\mathit{b}}$/${\mathit{V}}_{\mathit{c}\mathit{b}}$‖<0.08–0.13.

We derive a calculable upper limit on the mass of the lightest Higgs boson in perturbatively valid supersymmetric theories with arbitrary Higgs sectors. We assume a supersymmetry spectrum around or below 1 TeV and the standard model gauge symmetry, but place no restrictions on the Higgs sector. We estimate ${\mathit{m}}_{\mathit{h}}^0$<146 GeV for ${\mathit{M}}_{\mathit{t}}$≳100 GeV from all effects except possible additional heavy fermions beyond top (which could increase the limit approximately 12 GeV per extra family); for 60≲100 GeV we find ${\mathit{m}}_{\mathit{h}}^0$<156 GeV. In most explicitly constructed models the lightest Higgs boson mass does not saturate the upper limit.

Two-way decay has been observed between superdeformed bands in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Hg}$. It is proposed the decays have M1 multipolarity and connect signature partner bands. Candidates for the two-way gamma decays connecting superdeformed bands are observed for the first time.

The rotational spectrum of ${}_{}{}^{168}{}_{}{}^{}\mathrm{Yb}$ is calclated by diagonalizing different effective interactions within the basis of unperturbed rotational bands provided by the cranked shell model. A transition between order and chaos taking place in the energy region between 1 and 2 MeV above the yrast line is observed, associated with the onset of rotational damping. It can be related to the higher multipole components of the force acting among the unperturbed rotational bands.

This Letter demonstrates that the parity degeneracy of isolated vibration-rotation states of a rigid molecule can be removed by hyperfine interactions. Hyperfine structures of infrared transitions in ${\mathrm{PH}}_3$ are obtained, by saturation spectroscopy around 10 μm. One of these is used to demonstrate unequivocally that degenerate states of opposite parity are separated by the proton hyperfine interactions. We show that alternative explanations involving the physical inversion of the molecule are completely inconsistent with the details of the spectra obtained. In addition to the splitting conclusion, which has very wide generality, new confidence limits are placed on the possible inversion splitting.

A correlation of secondary electrons emitted in the forward and in the backward directions has been studied for 1.8 MeV/u Ar ions bombarding carbon foils. Appreciable correlation has been observed not only for thin targets but also for thick targets where no correlation was expected. It is shown that a classical trajectory Monte Carlo simulation including conversion of bulk plasmons into electron-hole pairs which extends over the target can reproduce the observation qualitatively.

The atomic recoil from the absorption of up to 60 photons is measured using an atom interferometer. We determine ħ/${\mathit{m}}_{\mathrm{Cs}}$ with a precision of ${10}^{\mathrm{-}7}$ in 2 h of integration time.

Steady-state solutions of double-beam polarization-dependent two-photon absorption (PDTPA) are examined. A new basis is used to solve the master equation for PDTPA. It is found that these steady-state solutions are composed of nontrivial states of the two initial beams. This is in disagreement with the predictions of two-photon absorption ignoring the vector nature of the electromagnetic field.

The parameter space of the Hénon map is reported to contain a regular structure-parallel-to-structure sequence of shrimp-shaped robust isoperiodic domains. They appear densely concentrated on a neighborhood along a main α direction, extending across both orientation-preserving and -reversing domains. There is also a secondary β direction, roughly perpendicular to a very dense ‘‘foliation of legs’’ emanating from the isoperiodic domains. Familiar bifurcation phenomena observed in unimodal maps correspond to particular cuts along the β direction. The α direction is rich in new phenomena. The topology along α is conjectured to be typical of bimodal maps.

The first infrared vibrational photon echo experiments conducted in a liquid and a glass are reported. The experiments were performed on the CO stretching mode of tungsten hexacarbonyl at 5.1 μm (1960 ${\mathrm{cm}}^{\mathrm{-}1}$) in 2-methyltetrahydrofuran over the temperature range 300 to 16 K using picosecond pulses from the free electron laser at Stanford University. In addition, the first vibrational population relaxation measurements spanning a temperature range that takes a system from a liquid to a supercooled liquid to a glass are reported.

The temporal evolution of global modes is studied, which are time-harmonic solutions of the linear disturbance equations, subject to homogeneous boundary conditions in all space directions. As basic flow we consider weakly nonparallel three-dimensional shear flows. A necessary condition for the existence of a global mode is the presence of at least two branches of the local dispersion relation and a location where they coalesce. It leads to a mode coupling in a neighborhood of that point. To analyze the mode coupling the uniform asymptotic description of Kravtsov and Ludwig is employed which also yields a general formula for the global eigenfrequency.

A phenomenological description of the dynamical correlations in a fluid confined between two parallel solid walls, using a generalization of Onsager’s theory of fluctuations, is presented. Besides the bulk viscosity, this description involves parameters characterizing the boundary conditions. Correlations functions obtained in equilibrium molecular dynamics simulations are very well described within this framework. Featureless walls yield perfect slip boundary conditions, while corrugated walls in most cases correspond to stick boundary conditions. Only for very small corrugation amplitudes is it necessary to introduce a finite slipping length.

A variational principle for thermostated nonequilibrium steady states recently proposed by Evans and Baranyai [Phys. Rev. Lett. 67, 2597 (1991)] is analyzed by means of a model kinetic equation for dilute gases. It is shown that the principle does not apply exactly, although deviations from it are small, especially when the gradients are not very large.

Alfvén-ion-cyclotron modes are generated over a wide range of anisotropy parameter ${\mathrm{\beta }}_{\mathrm{\perp }}$(${\mathit{T}}_{\mathrm{\perp }}$/${\mathit{T}}_{\mathrm{\parallel }}$${)}^2$ in ICRF-heated central cell plasmas of the GAMMA 10 tandem mirror. The fluctuations are observed at a small driving force in the convectively unstable region predicted theoretically in an infinite plasma. Before reaching the β limit of ${\mathrm{\beta }}_{\mathrm{\perp }}$=3.52×(${\mathit{T}}_{\mathrm{\parallel }}$/${\mathit{T}}_{\mathrm{\perp }}$${)}^2$, above which the absolute instability is predicted, relaxation of pressure anisotropy is observed for the first time by use of an array of diamagnetic loops together with a Faraday cup and secondary-electron emission detectors.

Large bandwidth in lasers for inertial confinement fusion is potentially capable of controlling laser-plasma instabilities. We have demonstrated the efficient generation of large bandwidth, Δν/ν=2%, in a frequency-doubled Nd:glass laser in 527 nm, using stimulated rotational Raman scattering in atmospheric pressure nitrogen gas. Its use in a fusion laser would involve the use of a multilens array to produce multiple foci where the broadband conversion takes place. This technique is also effective for frequency tripled or quadrupled lasers at 351 or 263 nm.

Positional anchoring of the smectic-A(SA) liquid crystal 40.8 at a glass plate interface is measured with a micromechanical technique: stress oscillations at layer thickness scale are observed under shear normal to the layers. Similar oscillations are observed on its smectic-B phase, and previously in plastic crystals. These oscillations are explained by shear-induced surface melting and recrystallization. The corresponding SA positional anchoring energy is ∼${10}^{\mathrm{-}8}$–${10}^{\mathrm{-}9}$ J/${\mathrm{m}}^2$. This unidimensional periodic melting is a model for solid friction in soft matter.

The relaxation of light-induced tilt-angle changes in a ferroelectric smectic-${\mathit{C}}^{\mathrm{*}}$ liquid crystal is investigated with picosecond laser-induced dynamic gratings. Grating buildup and decay is monitored by diffraction of a cw laser beam. It is shown that reorientation of the liquid-crystal molecules is achieved by rapid optical heating and follows the temperature rise with a characteristic time constant, depending on temperature. The observed rise times correspond to the soft-mode relaxation of the order parameter in a Landau theory describing the smectic-${\mathit{C}}^{\mathrm{*}}$–smectic-A phase transition.

The structure of β-cristobalite has been studied though a first-principles total-energy minimization in the local-density approximation using a Car–Parrinello-type algorithm combined with the Vanderbilt ultrasoft pseudopotential scheme. It was found that the hypothetical ordered structure proposed by Wright and Leadbetter is favored and the resulting structural parameters agree very well with experiment. Also, correlated relaxation of Si and O atoms toward α-cristobalite positions in the vicinity of domain boundaries is indicated.

Lennard-Jones monolayers are shown by molecular dynamics simulation to exhibit a self-healing behavior which involves a rapid condensation of vacancies into dislocation dipoles. An associated collapse of the shear modulus similar to the Kosterlitz-Thouless dipole dissociation occurs for high vacancy concentrations. By contrast monolayers having nearest neighbor piecewise linear interactions are found to cavitate by agglomeration of vacancies into clusters.