We have estimated the power spectra of density fluctuations produced by cosmic strings with neutrino hot dark matter (HDM). Normalizing at 8${\mathit{h}}^{\mathrm{-}1}$ Mpc [where h=${\mathit{H}}_0$/(100 km/sec Mpc) and ${\mathit{H}}_0$ is the Hubble constant] we find that the spectrum has more power on small (≲10${\mathit{h}}^{\mathrm{-}2}$ Mpc) scales than HDM+ inflation, less than cold dark matter (CDM) + inflation, and significantly less than CDM + strings. With HDM, large wakes (∼20${\mathit{h}}^{\mathrm{-}2}$ Mpc) give significant contribution to the power on the galaxy scale and may give rise to large sheets of galaxies.

A systematic analysis of renormalization schemes and a general proof of the precise formulation of the equivalence theorem are given in the ${\mathit{R}}_{\xi }$ gauge for both the SU(2${)}_{\mathit{L}}$ and the SU(2)×U(1) theories. The precise formula for the modification factor ${\mathit{C}}_{\mathrm{mod}}$ is obtained, and a convenient particular scheme in which ${\mathit{C}}_{\mathrm{mod}}$ is exactly unity is proposed. ${\mathit{C}}_{\mathrm{mod}}$ in other schemes are discussed up to one loop in the heavy Higgs boson limit.

Vacuum polarization effects are nonperturbatively incorporated into the photon propagator to eliminate the severe infrared problems characteristic of (2+1)-dimensional QED (${\mathrm{QED}}_3$). The theory is thus rephrased in terms of a massive vector boson whose mass is ${\mathit{e}}^2$/8π. Subsequently, it is shown that electron-electron bound states are possible on ${\mathrm{QED}}_3$.

Nuclear decay via neutrino-pair production is found to have a large density dependence because of intermediate electromagnetic couplings to electrons. These are calculated in a relativistic random phase approximation. The decay rate for vector (Fermi) transitions producing electron type neutrino pairs can be enhanced by ${10}^5$ or more at densities relevant for stellar collapse. Axial-vector (Gamow-Teller) transitions are not enhanced.

The quasielastic scattering of the exotic ‘‘halo’’ nucleus ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ has been studied at an energy of 60 MeV/nucleon and compared with that of the A=11 isobar ${}_{}{}^{11}{}_{}{}^{}\mathrm{C}$. The prediction of enhanced refraction in the former system is confirmed, as is the need for very long-range absorption. No evidence is found for an Airy minimum in the far-side scattering.

A weak feature observed at 323.4±0.2 Å in the foil-excited spectrum of a helium ion beam is ascribed to radiative autoionization from the triply excited 2${\mathit{p}}^3$ ${}_{}{}^4{}_{}{}^{}$S state of the negative helium ion. The observation is consistent with recent calculations of the position and possible decay modes of the hitherto unobserved state.

Efficient excess-photon detachment to lowest nonvanishing order is observed with long (∼0.7 ns) optical pulses and intensities of ≤6×${10}^9$ W/${\mathrm{cm}}^2$. A Feshbach (‘‘window’’) resonance in ${\mathrm{Cs}}^{\mathrm{-}}$ suppresses single-photon detachment, while simultaneously enhancing the probability of absorption of one or more excess photons. The perspectives for future spectroscopic excess-photon detachment and studies of direct two-electron multiphoton detachment are briefly discussed.

We have measured the ion yields for helium ionized by 120 fs, 614 nm laser pulses for intensities near ${10}^{16}$ W/${\mathrm{cm}}^2$. We have found that for these ultrashort pulses the ${\mathrm{He}}^{+2\mathrm{}}$ data exhibit a feature which saturates in parallel with the ${\mathrm{He}}^{+}$ signal indicating that the ionization may proceed nonsequentially. We propose a new mechanism, which can exist only in the tunneling regime, for such nonsequential ionization.

Dissociative ionization of ${\mathrm{N}}_2$ induced by intense picosecond radiation has been studied. A two-step multiphonon model, based on ionization of ${\mathrm{N}}_2$ through vertical transitions and spontaneous dissociation of ${\mathrm{N}}_2^{\mathit{z}+}$ (Z≥2) via Coulomb and non-Coulombic potentials curves, is presented to explain the origin of the kinetic energies of atomic ions observed. The model predicts that dissociation occurs near the internuclear separation of the neutral, charge-asymmetric dissociation channels are important, and dissociation via Coulomb curves will only be observed for pulses with extremely short rise times.

We have measured whole-pulse photon statistics of macroscopic twin pulses of light generated by coherently seeding a two-mode optical parametric amplifier equally in each mode. We are able to produce 300 ps, near-transform-limited twin pulses (∼${10}^6$ photons) with a difference photon number having a variance measured to be 73% below the shot-noise level. We have measured probability distributions of the photoelectron difference number, which are the only photoelectron distributions in the macroscopic regime which cannot be explained using standard semiclassical detection theory.

It is shown that signed measures (i.e., measures that take on both positive and negative values) may exhibit an extreme form of singularity in which oscillations in sign occur everywhere on arbitrarily fine scale. A cancellation exponent is introduced to characterize such measures quantitatively, and examples of significant physical situations which display this striking type of singular behavior are discussed.

Experiments are performed which illustrate the properties of damped traveling waves in diffusive media. Our observations demonstrate the manipulation of these waves by adjustment of the photon diffusion coefficients of adjacent turbid media. The waves are imaged, and are shown to obey simple relations such as Snell’s law. The extent to which analogies from physical optics may be used to understand these waves is further explored, and the implications for medical imaging are briefly discussed.

The external vibrations in solid ${\mathrm{C}}_{60}$ were studied by means of inelastic neutron scattering. The translational spectrum extends to 6 meV at room temperature and hardens by 5% on cooling below ${\mathit{T}}_{\mathit{s}}$. Narrow librational excitations were observed up to temperatures very close to ${\mathit{T}}_{\mathit{s}}$ at energies around 2.4, 3.6, and 4.6 meV. Calculations based on a van der Waals potential give about the correct frequency range for the translations, but frequencies considerably too low for the librations. Bond-charge models give better results only for an unrealistic choice of parameters.

The far-infrared transmission spectrum of solid ${\mathrm{C}}_{60}$ is presented in the 7.5–420-${\mathrm{cm}}^1$ range at 2 K. It is found that the cubic environment of ${\mathrm{C}}_{60}$ molecules in the solid results in the activation and splitting of silent molecular modes. The two infrared-active translational modes propagating in the ${\mathrm{C}}_{60}$ solid are observed below 60 ${\mathrm{cm}}^{\mathrm{-}1}$. Their energies are found to be significantly higher than predicted by molecular-dynamics simulations. This suggests a harder intermolecular potential for solid ${\mathrm{C}}_{60}$ than presently used in these simulations.

The probability ${\mathit{R}}_{\mathit{L}}$(p) for a site percolation cluster to span a square lattice of side L at occupancy p is reexamined using extensive simulations and exact calculations. It is confirmed that ${\mathit{R}}_{\mathit{L}}$(${\mathit{p}}_{\mathit{c}}$)→1/2 as L→∞ in agreement with universality but not with renormalization-group theory. Many estimates of ${\mathit{p}}_{\mathit{c}}$ that derive from ${\mathit{R}}_{\mathit{L}}$(p) are shown to scale with L more weakly than normal finite-size scaling, and the value ${\mathit{p}}_{\mathit{c}}$=0.592 7460±0.000 0005 is determined.

We study the topological properties of the ensemble of cells with trivalent vertices in the plane. The problem is equivalent to counting planar Feynman diagrams with a cubic interaction. This ensemble is also the equilibrium state of a topological model of cellular structure, obtained by applying repetitively a topological flip transformation to any initial configuration of cells with trivalent vertices. We give analytical expressions for two-cell correlations; in particular, we give the analytical form of the average number m(n) of edges of cells adjacent to an n-sided cell. These results are confirmed by simulations.

We report state-specific kinetic energy distributions for ${\mathrm{D}}_2$ desorbed from Cu(111), which we have analyzed to obtain state-specific functions for adsorption probability versus kinetic energy. The dependence of these functions on vibrational state is in agreement with previous adsorption measurements. The dependence of the adsorption functions on rotational state J reveals a complex dynamical role for rotation in activated adsorption. As a function of J, the translational energy required for adsorption first increases slightly as J increases from 0 to 5 and then decreases markedly with higher J.

The recently observed behavior of helium films adsorbed on alkali metal surfaces has confirmed earlier ideas about wetting and prewetting transitions. However, a quantitative discrepancy between the predicted and observed wetting temperature suggests that a reexamination of the energetics of adsorbed helium films is required. We show how the zero point phonon energy of an alkali-vapor interface can dramatically change the wetting properties of these substrates, in accord with experiment. We investigate the dependence on the exposed facet of the crystal surface. For Rb and Cs, the (110) face is predicted to be wet at zero temperature while the (100) face is not. An isotope effect is also predicted.

We show that the many-body interactions among excitons govern the temporal line shape of the coherent (free induction decay) emission from semiconductor quantum walls. At low exciton densities, they become the dominant contribution to the emission.

Fullerene tubules are shown to be highly polarizable ‘‘molecular straws’’ capable of ingesting dipolar molecules. Local-density-functional calculations on HF molecules within a finite-length tubule, of size 144 atoms, demonstrate this effect. The energy of incarceration is several times the thermal ambient at room temperature. These calculations, now feasible on desktop workstations, open the way to the study of nanoscale capillarity and to, perhaps, precise control over shielding of specific ‘‘guest’’ compounds from external electric and magnetic fields.