We derive new bounds on scalar leptoquark couplings from ${\mathit{K}}^0$-K${\mathrm{¯}}^0$, ${\mathit{D}}^0$-D${\mathrm{¯}}^0$, and ${\mathit{B}}^0$-B${\mathrm{¯}}^0$ mixing. Although leptoquarks contribute to these processes only at one loop, their contribution is large, due to the lack of Glashow-Iliopoulos-Maiani cancelation. Our bounds have two important features: (i) They bound ${\mathit{g}}^4$/${\mathit{M}}^2$, in contrast to the hitherto known bounds on ${\mathit{g}}^2$/${\mathit{M}}^2$, and are consequently stronger at high masses. (ii) The bound from ${\mathit{D}}^{0\mathrm{-}}$D${\mathrm{¯}}^0$ mixing is the first flavor changing neutral current bound in the up sector for chirally coupled leptoquarks, and is similar in strength to the ${\mathit{K}}^{0\mathrm{-}}$K${\mathrm{¯}}^0$ and ${\mathit{B}}^{0\mathrm{-}}$B${\mathrm{¯}}^0$ bounds. Together, these bounds strongly constrain any leptoquark that couples to left-handed quarks.

In an extended mean field theory, we find a large class of bound multistrange objects, formed from combinations of {p,n,Λ,${\mathrm{\Xi }}^0$,${\mathrm{\Xi }}^{\mathrm{-}}$} baryons, which are stable against strong decay. We predict a maximal binding energy per baryon of ${\mathit{E}}_{\mathit{B}}$/A≊-21 MeV, strangeness per baryon ${\mathit{f}}_{\mathit{s}}$≊1.2, charge per baryon ${\mathit{f}}_{\mathit{q}}$≊-0.1 to 0, and baryon density 2.5–3 times that of ordinary nuclei. For A≥6, we obtain stable combinations involving only {Λ,${\mathrm{\Xi }}^0$,${\mathrm{\Xi }}^{\mathrm{-}}$} hyperons.

We sketch two rigorous proofs of the stability of the hydrogen molecule in quantum mechanics. The first one is based on an extrapolation of variational estimates of the ground state energy of a positronium molecule to arbitrary mass ratios. The second one is an extension of Heitler-London theory to nuclei of finite mass.

Using recently developed quantum wave function techniques, we have performed a simulation of ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ atoms in a one-dimensional optical molasses, formed from counterpropagating laser beams with orthogonal linear polarizations. Both internal and external degrees of freedom are treated quantum mechanically in one dimension and the spectrum of resonance fluorescence is calculated and compared to recent experiments. Excellent agreement is obtained for the spectrum and additional insight is gained into the experimental evidence for quantized motion in the optical potentials.

We propose a method of probing a system of cooled atoms in a trap using short laser pulses. Above the critical temperature for Bose-Einstein condensation such a system scatters very weakly. Coherent scattering occurs primarily in the forward direction. Below the critical temperature, the number of scattered photons increases dramatically and the scattered light is emitted in the solid angle determined by the size of the condensate.

We have measured integral elastic cross sections for ground state ${}_{}{}^4{}_{}{}^{}\mathrm{-}_{}^4{}_{}{}^{}$He scattering at collision energies from 1.35 to 0.5 K using a novel atomic beam apparatus built into a dilution refrigerator. Scattering is almost pure s wave, and is predicted to be enormous due to a possibly bound state near the continuum. The effective integral cross section ranges from 20 to 1000 A${\mathrm{̊}}^2$ as collision energy is reduced in our experiment. These cross sections are in agreement with the values predicted using the latest analytical potential of Aziz and Slaman.

Experimental evidence of the existence of a bound state of the ${\mathrm{HeH}}^{2+}$ molecular ion is presented. Bates and Carson predicted a bound 2pσ state in spite of the strong repulsion potential between the two nuclei. Decay is expected by an electronic transition to the 1sσ repulsive ground state with a mean lifetime of about 1 nsec and a kinetic energy release of ∼7 eV. A novel coincidence technique was developed for the measurement of metastable molecular ions which dissociate in flight before reaching the detector. The metastable ${\mathrm{HeH}}^{2+}$ ions were produced in collisions of 900 keV ${\mathrm{HeH}}^{+}$ with Ar and analyzed within a few nanoseconds using a small powerful analyzing magnet. The coincidences between the ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ fragments detected at the deflection angle associated with the ${\mathrm{HeH}}^{2+}$ molecular ion indicate clearly that it was formed in a bound state during the collision and decayed after passing through the analyzer. The radial distribution of fragments hitting the detector was also measured and the kinetic energy-released in the dissociation was determined. This energy was found to be consistent with the one expected for the decay of ${\mathrm{HeH}}^{2+}$ by 2pσ to 1sσ transition.

I calculate the coherent population trapping states of a three-level system interacting with two quantized fields. I show that such trapping states have novel properties. For example, I show that the trapping states for a Λ system involve the production of radiation fields with matched photon statistics. I discuss a method for producing these trapping states. For a ladder system, the trapping states even lead to the nonclassical character of the radiation fields.

We show that the uncertainty in the relative quantum phase of two fields propagating in the arms of a Mach-Zehnder interferometer can be reduced to the Heisenberg limit by driving the interferometer with two Fock states containing equal numbers of photons. This leads to a minimum detectable phase shift far below that of any interferometer driven by a coherent light source.

We report a new phenomenon observed along a crisis locus when two control parameters of physical models are varied simultaneously: the existence of one or several vertices. The occurrence of a vertex (loss of differentiability) on a crisis locus implies the existence of simultaneous sudden changes in the structure of both the chaotic attractor and of its basin boundary. Vertices correspond to degenerate tangencies between manifolds of the unstable periodic orbits accessible from the basin of the chaotic attractor. Physically, small parameter perturbations (noise) about such vertices induce drastic changes in the dynamics.

We have found experimentally that the flow of sand in an hour glass is oscillatory in a certain range of parameters. The oscillatory motion results from a coupling between the flow of sand and convection of air through the sand matrix. The period of the oscillation is remarkably insensitive to the grain size, while the mass of the sand contained in one period strongly depends on it.

The Landau-Ginzburg equations used to describe periodic spatial patterns in two dimensions are extended to a set of spatiotemporal equations. The extension is determined by the requirement that the equations of motion commute with translations, reflections, and rotations in the plane. This simple model produces a variety of complex structures similar to those observed in chemical reactions, ferrofluids, Rayleigh-Bénard convection, and magnetic bubble materials.

We observe the (r,θ) drift motion of two nearly identical magnetized electron columns bounded by a cylindrical wall. In the 2D E×B drift approximation, these columns are vortices evolving according to the Euler equation. We observe stable and unstable equilibria in which the vortices orbit about the center of the cylinder. The equilibrium positions, oscillation frequencies, and instability rates for these spatially extended vortices agree well with the predictions of integrable point vortex theory, apparently because surface waves and shape distortions do not couple to the center-of-mass motion.

A useful physical model for superfluid turbulence considers the flow to consist of a dense tangle of vortex lines which evolve and interact. It has been suggested that these vortex lines can dynamically reconnect upon close approach. Here, we consider the nonlinear Schrödinger equation model of superfluid quantum mechanics, and use numerical simulation to study this topology changing core-scale process. Our results support the idea that vortex reconnection will occur whenever filaments come within a few core lengths of one another.

A feasibility test of a new method to polarize beams of strongly interacting charged particles circulating in a storage ring is described. The stored particles, here protons, pass through a polarized hydrogen gas target (thickness 6×${10}^{13}$ H/${\mathrm{cm}}^2$) in the ring some ${10}^{10}$ times and become partially polarized because one spin state is attenuated faster than the other. The polarization buildup is clearly demonstrated in the present experiment.

X-ray diffraction and calorimetry data on cubic ${\mathrm{Na}}_{\mathit{x}}$${\mathrm{C}}_{60}$(1<x<3) reveal orientational ordering transitions at ${\mathit{T}}_{\mathit{m}}$ above that of pure ${\mathrm{C}}_{60}$, e.g., ${\mathit{T}}_{\mathit{m}}$(x=1.3)=325 K. The ordered phases are the same as in pure ${\mathrm{C}}_{60}$: simple cubic, space group Pa3¯, but the orientations in the disordered phase are more restricted. We explain how Na stabilizes the ordered phase to rather high T, while K and Rb do not, in terms of Coulomb interactions between ${\mathrm{C}}_{60}$ molecules and and Na ions which we calculate from the local charge density of ${\mathrm{C}}_{60}$.

The tip-surface interactions in scanning tunneling microscopy (STM) of the Si(100) surface are investigated with ab initio total energy pseudopotential calculations. The results of the calculations lead to a new understanding of the microscopic STM measurement process. It is found that under typical conditions the influence of the tip is large enough to effectively flip a dimer on this surface. This leads to a reinterpretation of the ‘‘symmetric’’ dimer STM image as an asymmetric dimer configuration that flips as it follows the motion of the scanning tip.

The first detailed x-ray study of static undulations in a liquid-crystal polymer is presented. By examining the nonspecular diffuse scattering from a 30-layer ferroelectric liquid-crystal polymer film, it is shown that the layer fluctuations are induced by the roughness of the film-substrate interface. This contrasts with the case of free-standing films wherein thermal fluctuations play the major role.

We present evidence that nuclear recoils in silicon at cryogenic temperatures result in a larger ballistic component of phonons than do equal-energy electron recoils. A 300 μm thick crystal of pure silicon was instrumented on both sides with superconducting titanium transition-edge sensors, and the phonon ballistic energy fraction was determined by measuring phonon focusing effects. Comparison of the data with simulations indicates that this fraction is 1.${49}_{\mathrm{-}0.26}^{+0.34\mathrm{}}$ times higher (at 68% confidence level) for nuclear recoils than for electron recoils.

We propose a model whereby the average size of domains in a binary mixture undergoing spinodal decomposition near a wall can achieve growth exponents much larger than the usual bulk value of 1/3. The accelerated growth is associated with the nonwetting phase coarsening anisotropically against a wall coated with the wetting phase. The larger exponents arise from the coupling of domain coalescence with Lifshitz-Slyozov type growth, modified to include the geometric constraint of growth near a wall. We include experimental tests of these ideas.