We demonstrate the observational viability of having an exactly massless dilaton field couple with gravitational strength to most matter in the Universe. This is done by constructing a generalized Jordan-Brans-Dicke model in which the scalar couples with different strengths to visible and to conjectured ‘‘dark’’ matter. In this model, improved Ġ measurements may provide nontrivial bounds on the coupling constants of the dilaton to matter.

We propose a nonperturbative definition of two-dimensional quantum gravity, based on a double-scaling limit of the random-matrix model. We derive an exact differential equation for the partition function of two-dimensional gravity coupled to conformal matter as a function of the string coupling constant that governs the genus expansion of two-dimensional surfaces, and discuss its properties and consequences. We also construct and discuss the correlation functions of an infinite set of local operators for spherical topology.

We show how wormholes and Peccei-Quinn symmetries are in fact complementary in solving the strong CP problem. On the one hand, Peccei-Quinn symmetries are shown to provide us with a wormhole parameter that couples only to the QCD anomaly. This then allows us to implement the wormhole solution to the strong CP problem constructed previously by the present authors as well as by Preskill, Trivedi, and Wise. On the other hand, wormholes are shown to drive the axion mass to zero or to the wormhole scale, thus avoiding the axion-energy-density crisis in either case.

If the Higgs sector (like the fermion sector) in a supersymmetric model consists of several generations, then a basis in which only one generation gets vacuum values can be chosen. The other generations have been largely ignored, but can be interesting. For example, in the minimal model, if tree-level flavor-changing neutral currents are eliminated by some symmetry, then the lightest of these scalars is stable and the second lightest is only slightly more massive. The lightest is a superb dark-matter candidate, and if light enough, gives an unusual and detectectable signature at the SLAC Linear Collider or the CERN $e^{+}$$e^{\mathrm{-}}$ collider LEP.

The chiral Schwinger model is reexamined by using chiral bosonization. The Lagrangian is obtained as a gauged Floreanini-Jackiw Lagrangian. We get a bosonic solution which contains one massive free boson and one (free) self-dual field.

A search for the top quark in p¯p collisions at a center-of-mass energy of 1.8 TeV using the Collider Detector at Fermilab is described. A study of events selected by requiring an energetic electron, missing transverse energy, and two or more jets excludes at 95% confidence level the standard-model production and decay of tt¯ pairs if the top-quark mass is between 40 and 77 GeV/$c^2$. The observed electron + multijet data are consistent with W-boson production.

A search for tt¯→eμ+X in pp¯ collisions at s√¯ TeV is described. The production and decay of top-quark–antiquark pairs is considered in the context of the standard model. The analysis is based on data with an integrated luminosity of 4.4 ${\mathrm{pb}}^{\mathrm{-}1}$ recorded with the Collider Detector at Fermilab. An upper limit on the tt¯ cross section is obtained, and the top quark in the mass range 28–72 GeV/$c^2$ is excluded at the 95% C.L. The same limits apply to a possible fourth-generation, charge -(1/3, b’ quark, decaying via the charged current.

An analysis of W- and Z-boson production using data from the Collider Detector at Fermilab at √s =1.8 TeV yields σ(W→ev)/σ(Z→ee)=10.2±0.8(stat)±0.4(syst). The width of the W boson, Γ(W), and a limit on the top-quark mass independent of decay mode are extracted from this measurement.

The two-jet differential cross section ${\mathit{d}}^3$σ(p¯p→jet 1+jet 2+X)/${\mathit{dE}}_{\mathit{t}}$d${\mathrm{\eta }}_1$d${\mathrm{\eta }}_2$, averaged over -0.6≤${\mathrm{\eta }}_1$≤0.6, at √s =1.8 TeV, has been measured in the Collider Detector at Fermilab. The predictions of leading-order quantum chromodynamics for most choices of structure functions show agreement with the data.

Final-state interactions in K→ππ enhance the ΔI=(1/2 amplitude and suppress the ΔI=(3/2 one. The effect appears to be about an order of magnitude in the ratio of the rates and may be useful in reconciling the outstanding discrepancy between short-distance QCD corrections and experiment.

A search for the lepton-flavor number-violating decay $K^{+}$→${\pi }^{+}$${\mu }^{+}$$e^{\mathrm{-}}$ has been conducted at the Brookhaven Alternating Gradient Synchrotron. No candidates have been found which would be consistent with this decay mode. An upper limit on the branching ratio is placed at 2.6×${10}^{\mathrm{-}10}$, which can be combined with our previous result to yield an upper limit of 2.1×${10}^{\mathrm{-}10}$ at the 90% confidence level. A limit on the branching ratio for ${\pi }^0$→${\mu }^{+}$$e^{\mathrm{-}}$ of 1.6×${10}^{\mathrm{-}8}$ (90% C.L.) is also established.

We report a study of the hadronic branching fractions of the $D_s^{+}$ meson, which is used to extract an upper limit on the absolute branching fraction for $D_s^{+}$→φ${\pi }^{+}$. A search is made for fully reconstructed events from the reaction $e^{+}$$e^{\mathrm{-}}$→$D_s^{\mathrm{*}\pm }$$D_s^{\mp }$, $D_s^{\mathrm{*}\pm }$→γ$D_s^{\pm }$, using seven exclusive $D_s^{+}$ decay modes. The data sample of 6.30±0.46 ${\mathrm{ppb}}^{\mathrm{-}1}$ was collected at √s¯=4.14 GeV with the Mark III detector at the SLAC ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ storage ring SPEAR. No candidate events are observed. The measured relative $D_s^{+}$ branching fractions and σB($D_s^{+}$→φ${\pi }^{+}$) are used to establish the limit B($D_s^{+}$→φ${\pi }^{+}$)<4.1% at 90% confidence level.

The TPC/Two-Gamma facility at the SLAC $e^{+}$$e^{\mathrm{-}}$ storage ring PEP was used to study the reactions γ${\gamma }^{\mathrm{*}}$→η and γ${\gamma }^{\mathrm{*}}$→η’. The η${\gamma }^{\mathrm{*}}$γ and η’${\gamma }^{\mathrm{*}}$γ transition form factors were measured as functions of $Q^2$, the negative of the invariant mass squared of the tagged photon, in the range 0.1<$Q^2$<7 ${\mathrm{GeV}}^2$. These determinations of the electromagnetic structure of the η and η’ mesons are consistent with both vector-meson dominance and QCD. They also provide new measurements of the pseudoscalar mixing angle and decay constants.

We have measured np→d${\pi }^0$ cross sections at eleven beam energies within 16 MeV of threshold. Total cross sections are only 0.67±0.10 of the value which has been generally accepted for s-wave pion production strength near threshold. The differential cross sections are anisotropic at only 1 MeV (c.m.) above threshold. Our results are compared to ${\pi }^{+}$d→pp data and to predictions of two models.

We compare the radiation output from simulations of a finite-pulse high-power laser for several tapering rates. A fast taper leads to a tenfold increase in efficiency as compared to a slow taper, with little change in peak radiation intensity. The enhanced power for fast tapering rates is due to an increase in the optical pulse cross section, brought about by a reduction in refractive guiding. This is analyzed by an envelope equation for the radiation beam. For the tapering rates leading to the highest powers, the optical pulse is virtually free of sideband modulation.

In the opening gap between two moving surfaces, the interface between air and a viscous fluid can form a linear pattern of regular cells analogous to those of directional solidification. Depending on the values of the surface velocities, this pattern destabilizes in different ways. One regime presents the main characteristics of spatiotemporal intermittency of the type observed in the Kuramoto-Sivashinsky model. In the other, the cells become a propagative structure. Near one of the thresholds they show up as solitary waves; above, they form traveling domains of increasing size.

We present a molecular-dynamics simulation of the dynamical properties of a 2D Rb liquid intercalated in a periodic graphite host. Using an 864-atom system we show that this dynamical response consists of both solid and liquid features well above the melting point, as indicated in the neutron experiments of Zabel and co-workers, and may be characterized by floating (time-dependent) domains of briefly registered ions which, during their ∼26-ps lifetime, show phononlike behavior and a Debye-Waller factor in excellent agreement with the experiments of Kamitakahara and Zabel.

Anisotropies of the visible-near-ultraviolet dielectric responses of various (001) GaAs molecular-beam-epitaxy growth surfaces are measured at temperature using a new optical double-modulation technique and a low-strain fused-quartz window. Tight-binding calculations identify structure at 1.8 eV with Ga dimers and at 2.6 and 4.1 eV with As dimers. Transient behavior on interruption of As flux is substantially altered by misorientation, suggesting substantially different terrace properties for vicinally cut surfaces.

Results of the low-temperature precipitation of interstitial Fe (≊250 °C) in Czochralski-grown Si after different annealing treatments for the precipitation of oxygen are presented. It is concluded that the Fe solubility is not affected by the oxygen-precipitation process. The Fe-precipitation kinetics are found to be strongly accelerated by oxygen-precipitation–induced defects. Based on the results the mechanism of internal gettering is derived. For the first time the contribution of oxygen precipitates and dislocations to the internal-gettering process have been determined quantitatively.

We have imaged for the first time the atomic structure of a quasicrystal using a scanning tunneling microscope. The structure of the decagonal ${\mathrm{Al}}_{65}$${\mathrm{Co}}_{20}$${\mathrm{Cu}}_{15}$ quasicrystal is described by a pentagon-center-decorated pentagonal quasilattice giving strong evidence for a tiling model. The scanning-tunneling-microscope measurements of the surface are in good agreement with the high-resolution x-ray-diffraction measurements of the bulk.