Bond-energy correlation functions are calculated exactly for a planar Ising model in finite-size strip geometry for subcritical temperatures with surface fields of either equal or opposite sign applied to opposite edges. We show that the Wulff construction (surface free-energy minimization) applied to the bubble model for the 2-point energy correlation function gives exact results and demonstrates the significance of wetting phenomena.

A direct test for deterministic dynamics can be established by measurement of average directional vectors in a coarse-grained d-dimensional embedding of a time series. Theoretical analysis of the statistical properties of a random time series using the same embedding technique is possible by consideration of classical results concerning random walks in d dimensions. Examples are given to show the clear differences between deterministic dynamics, such as may be generated by chaotic systems, and stochastic dynamics.

The loop-space representation based on Ashtekar’s new variables has allowed for the first time the construction of quantum states of the gravitational field. However, all states known up to the present were associated with spacetime metrics that were everywhere degenerate. In this Letter we present a new exact solution of the constraint equations of quantum gravity that is the first quantum state of the gravitational field known to be associated with a not-everywhere-degenerate metric. The state is associated with the second coefficient of the Alexander-Conway polynomial of knot theory.

We present a multigrid Monte Carlo algorithm with piecewise-linear interpolation operator for nonlinear σ models with global chiral SU(N)×SU(N) symmetry or ${\mathrm{CP}}^{\mathit{N}\mathrm{-}1}$ manifold. We demonstrate its efficiency in the two-dimensional SU(3)×SU(3) chiral model and the ${\mathrm{CP}}^3$ nonlinear σ model for correlation length up to 77 in lattice units. On lattices up to size 512×512 we achieve almost complete elimination of critical slowing down in the ${\mathrm{CP}}^3$ case, with a dynamical critical exponent ${\mathit{z}}_{\mathrm{MGMC}}$=0.2±0.1. Asymptotic scaling with the bare coupling does not appear to set in for the standard action of both models in the range of parameters studied.

We study effects of induced CP-nonconserving effective operators involving the gluon field strength as a result of integrating out the heavy-quark field which carries a chromoelectric dipole moment. The induced gluonic operators of dimension 8 may be the dominant mechanism for generating the neutron electric dipole moment.

From a retroactive data analysis, we obtain the first upper bound on the ‖ΔL‖=2 kaon decay ${\mathit{K}}^{+}$→${\mathrm{\pi }}^{\mathrm{-}}$${\mathrm{\mu }}^{+}$${\mathrm{\mu }}^{+}$: B(${\mathit{K}}^{+}$ →${\mathrm{\pi }}^{\mathrm{-}}$${\mathrm{\mu }}^{+}$${\mathrm{\mu }}^{+}$)<1.5×${10}^{\mathrm{-}4}$. We also discuss ${\mathit{K}}^{+}$→${\mathrm{\pi }}^{\mathrm{-}}$${\mathrm{\mu }}^{+}$${\mathit{e}}^{+}$ and ‖ΔL‖=2 decays of D and B mesons. We suggest experiments which can improve our limit and discuss the connection with direct searches for heavy neutrinos in ${\mathit{K}}_{\mathrm{\mu }2}^{+}$ decay.

We present results from searches for the top quark pp¯ collisions at the Fermilab Tevatron Collider. The data sample was collected during 1988–89 with the Collider Detector at Fermilab and has an integrated luminosity of 4.1 ${\mathrm{pb}}^{\mathrm{-}1}$. Our previous search for eμ final states for tt¯→eνb μνb¯ decays has been extended to include the ee and μμ channels. In addition, we have searched in each event with a high-transverse-momentum lepton accompanied by hadron jets for a low-transverse-momentum muon as a tag of a bottom quark in tt¯→lνbqq¯b¯ decays. A lower limit on the top-quark mass of 91 GeV/${\mathit{c}}^2$ is obtained at the 95% confidence level, assuming standard model decays.

We present a high-statistics, species-identified measurement of the W-to-Be per-nucleon cross-section ratio, ${\mathit{R}}_{\mathrm{W}/\mathrm{B}\mathrm{e}}$, for high-${\mathit{x}}_{\mathit{t}}$ hadrons and high-τ ${\mathit{h}}^{+}$${\mathit{h}}^{\mathrm{-}}$ pairs produced in p-A collisions at √s =38.8 GeV. The data extend to 0.62 in ${\mathit{x}}_{\mathit{t}}$ and 0.39 in √τ . For single hadrons, ${\mathit{R}}_{\mathrm{W}/\mathrm{B}\mathrm{e}}$ peaks at ${\mathit{p}}_{\mathit{t}}$≊5 GeV/c and decreases to ≊1 for mesons with pt>8 GeV/c. At fixed ${\mathit{p}}_{\mathit{t}}$, ${\mathit{R}}_{\mathrm{W}/\mathrm{B}\mathrm{e}}$ falls with √s . For symmetric pairs with √τ >0.28, ${\mathit{R}}_{\mathrm{W}/\mathrm{B}\mathrm{e}}$=0.84±0.02±0.07, suggesting a nuclear suppression of high-z fragmentation. ${\mathit{R}}_{\mathrm{W}/\mathrm{B}\mathrm{e}}$ increases with ${\mathit{p}}_{\mathrm{out}}$, indicative of constituent multiple scattering.

We have performed the first search for 3γ decays of the hypothesized ${\mathit{X}}^0$ particle, related to GSI ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ peaks, using positrons from ${}_{}{}^{68}{}_{}{}^{}\mathrm{Ga}$ decay striking a Be target and Ge detectors to search for 3γ events. The geometry of the experiment was optimized for detection of decays of the ${\mathit{X}}^0$ nearly at rest in the Be. No evidence is found for a stopped, unbound ${\mathit{X}}^0$ in the mass range 1.1–1.7 MeV.

In superdeformed, heavy nuclei at low spins, M1 transitions enhanced by internal conversion are expected to compete favorably with E2 γ rays. For strongly coupled bands with fairly large B(M1) values, the decay may proceed between the two signature partner bands with very few γ rays emitted. Measured E2 γ ray intensities may imply strict limits on the M1 strength. Experimental evidence for the M1 cross talk dominated by internal conversion is seen in superdeformed bands in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Hg}$.

We report the first observation of continuous-wave two-photon lasing in the optical regime, and demonstrate that its initiation requires the injection of a trigger pulse into the laser resonator. Successful operation of the two-photon laser relies on the use of a novel gain medium consisting of laser-driven, two-level atoms and the use of a high-finesse optical cavity to isolate the two-photon gain from competing processes. Threshold conditions for laser action are in good agreement with recent theoretical predictions.

New data for ${\mathit{n}}_0$=24,...,32 H atoms ionized by a linearly polarized, 9.908-GHz electric field are compared with calculations. Being more precise than laser multiphoton ionization experiments with tightly bound atoms, our experiments distinguish between tunneling through and classical escape over a slowly oscillating barrier and between one- and many-state dynamical processes. Formulas used to interpret low-frequency laser multiphoton ionization data poorly describe our results. Our data delineate ranges of validity of other partly successful models and are best reproduced by a new 3D semiclassical model.

The position of an atom passing through a standard light wave is localized by making a quadrature phase measurement on the light field. This localization can be thought of as the creation of a virtual slit (or slits) for the atom by the field measurement. Diffraction and interference behavior may be observed in the far field.

A new optical near-field microscope with a lateral resolution of 3 nm (λ/200) is presented. Resonantly excited extended surface plasmons generate an optical near field which is locally probed by a sharp tip. The interaction of the surface plasmons with the tip can be understood in terms of elastic plasmon scattering and radiationless energy transfer from the tip to the sample. The new technique may permit the detection and spectrscopic identification of single adsorbed molecules.

We report the first measurements of significant polarization of the He-like emission in a laser-produced plasma. From these measurements we infer a negative second-order (i.e., oblate) anisotropy of the electron velocity distribution function in the energy deposition region. This result is in agreement with our kinetic Fokker-Planck calculations which indicate non-Maxwell behavior and strong anisotropy due to nonlocal electron heat flow.

The inference of the electron temperature ${\mathit{T}}_{\mathit{e}}$ from the Landau cutoff of backscattered Raman spectra is tested by simultaneous Thomson scattering temperature measurements and compared with results of two-dimensional hydrodynamic computer simulations. If the threshold condition is calculated by using a detailed modeling of the instability, then all three indications of ${\mathit{T}}_{\mathit{e}}$ agree. In contrast, the often-used estimate of k${\lambda }_{\mathrm{De}}$≊0.3 for sizable damping typically overestimates the electron temperature by a factor of 1.5 to 2 in this case.

The asymptotic properties of a model of interacting linear polymer are studied exactly on Sierpinski gaskets. The model displays a new multicritical point corresponding to a collapse from linear into branched polymer, which is followed by a further transition into compact globule. Clear evidence of the first collapse is also obtained for a 2-tolerant trail model of the square lattice, previously introduced for the description of the FTHETA transition.

X-ray scattering studies on aligned films of binary mixtures of the normal alkanes ${\mathrm{C}}_{23}$${\mathrm{H}}_{48}$ and ${\mathrm{C}}_{28}$${\mathrm{H}}_{58}$ reveal, for the first time in such materials, the existence of a new equilibrium phase having the symmetry of a smectic crystal, possibly a hexatic. This phase occurs between the hexagonally packed ${\mathit{R}}_{\mathrm{II}}$ and the lower-temperature orthorhombic ${\mathit{R}}_{\mathrm{I}}$, plastic crystalline, layered, rotator phases. We argue that this loss of order is due to local distortion fluctuations in the hexagonal phase. Furthermore, we have identified an ABC-to-ABAB restacking transition within the ordered ${\mathit{R}}_{\mathrm{II}}$ phase.

The dielectric constants of betaine calcium chloride dihydrate have been measured under hydrostatic pressure (190≤ρ≤320 MPa) and at varying temperatures (140≤T≤210 K) in the region of structure branching processes between the 〈22〉 and 〈23〉 commensurate phases. Along the various phase boundaries the dielectric permittivity exhibits maxima, which have been attributed to an accumulation of structure branching processes, as predicted by statistical spin models. The accumulation points are quasitricritical points, which have not been observed before. Our results compare favorably with recent calculations based on the axial next-nearest-neighbor Ising model.

Gamma-ray emission from the recoil particle can have a large effect on the blocking dip observed in crystal blocking experiments. We demonstrate this effect experimentally, and give a theoretical description based on standard chaneling theory that is in good agreement with the measurement. We discuss the implications for lifetime measurements using the crystal blocking technique.