Nonlinear effects of self-gravitating systems in cosmology are considered on the basis of perturbation theory. In particular, we examine several cases in which evolution of the power spectrum of density fluctuations can be analytically calculated. In some cases, nonlinearity suppresses the growth of fluctuations relative to linear theory, and the power transfer via nonlinear mode coupling is sensitive to the specific shape of the underlying fluctuation spectrum. The result is in good agreement with recent numerical simulations.

The singular structure of the spacetime associated with a cosmic string interacting with either a plane-fronted gravitational wave or a pencil of electromagnetic radiation is analyzed. We find that depending on the value of the string constant the interaction can produce either a directional or an essential curvature singularity along the cosmic string.

We investigate many-body corrections to neutrino scattering from electrons and nuclei. The Coulomb correlations of the electrons screen the weak vector neutral current. Electron screening is important only for electron neutrinos (or antineutrinos) and most effective for neutrino energies of several MeV or less. At electron densities relevant for supernovae, the total quasielastic ν-e cross section can be reduced by 50%, and elastic neutrino-nucleus scattering by up to 85%.

We reconsider the problem of confinement in theories with fermions with a compact gauge symmetry in 2+1 dimensions. We show that, as a result of the lack of gauge invariance of the determinant of the Dirac operator with a monopole background, the monopoles do not contribute to the Euclidean path integral. This result implies that fermions carrying the fundamental charge are not confined and that the spectrum of chiral-spin-liquid phases of theories of high-temperature superconductors supports separation of spin and charge.

We have studied four-jet angular distributions using data collected with the VENUS detector at the KEK ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ collider at TRISTAN at c.m. energies between 54 and 64 GeV. The obseved angular distributions are consistent with QCD, but are inconsistent with the Abelian gluon model at the 5% significance level. We have further obtained 95%-confidence experimental bounds on the fundamental parameters of the SU(${\mathit{N}}_{\mathit{c}}$) local color symmetry.

If an SU(2)-singlet charge-2/3 quark exists, current data allow a wide range for the parameters of the 4×4 mixing matrix in which the usual ‘‘hard-lepton’’ signal of the top quark is suppressed. For a light Higgs boson, the top quark decays predominantly via the flavor-changing Yukawa interaction, thus evading the Fermilab Tevatron bounds on its mass. For a heavier Higgs boson, flavor-changing neutral-current decays become important, giving rise to anomalous Z-pair production, testable at the upgraded Tevetron, at the CERN Large Hardon Collider, and at the Superconducting Super Collider.

Polarized parton distribution functions for a hadron target are defined in terms of gauge-invariant correlation functions. The polarized gluon contribution to the ${\mathit{g}}_1$ structure function of the nucleon is computed using the modified minimal-subtraction scheme as a simple example of the calculational method. The gluon contribution to the integral of the ${\mathit{g}}_1$ structure function is shown to vanish.

The ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ spectrum resulting from ultrerelativistic heavy-ion collisions is shown to have a sharp resonance at an invariant mass M≊0.2${\mathit{T}}_{\mathit{c}}$ (≊40 MeV of typical ${\mathit{T}}_{\mathit{c}}$=200 MeV). Observation of this resonance would signal the existence of the quark-gluon plasma, confirm the first-order nature of the transition, and determine the value of ${\mathit{T}}_{\mathit{c}}$.

The existence of an I=0, ${\mathit{J}}^{\mathit{P}}$=$1^{\mathrm{-}}$ quasibound state in the ηNN-πNN coupled system is theoretically predicted with a mass of about 2430 MeV and a width 10–20 MeV. The three-body equation for the ηNN-πNN coupled system. The primary two-body interactions generating the bound state are (1) the NN interaction in the ${}_{}{}^3{}_{}{}^{}$${\mathit{S}}_1$${\mathrm{-}}^3$${\mathit{D}}_1$ state and (2) the πN and ηN coupled interaction in the ${\mathit{S}}_{11}$ state. A remarkable enhancement of the elastic cross section of η-d scattering near the ηd threshold is found, whose origin is in the pole structure of the I=0, ${\mathit{J}}^{\mathit{P}}$=$1^{\mathrm{-}}$ ηd scattering amplitude on the complex energy plane.

We analyze the excitation of atoms by intense pulsed laser fields and describe the formation of spatially extended wave packets and substantial inhibition of ionization. A number of physical effects lead to inhibited ionization: We establish through a combination of numerical and analytical methods that one such effect is Raman mixing of intermediate Rydberg levels.

This Letter proposes a new class of x-ray lasers that lase on several 4d→4p transitions ranging from 23 to 80 Å in Ni-like ions with atomic number Z=72 to 90 and are resonantly photopumped by Ly-α radiation from corresponding H-like ions with atomic number (Z-21)/3. This scheme is unique in that it consists of a family of resonant pairs working off the ground state of the laser ion. Calculations of the gain of these laser transitions in steady-state equilibrium plasmas are presented.

The radial transport of toroidal angular momentum and circulation in a tokamak resulting from diffusion that is poloidally asymmetric is shown to produce an instability of the poloidal rotation. This instability, due to Stringer, sets in where the local particle-confinement time is smaller than the damping time of poloidal flow and leads to poloidal velocity shar. The nonlinear interplay between the poloidal spin-up and turulence-driven anoamlous transport is shown to lead to bifurcated equilibria of the type observed in the L-to-H-mode transition in tokamaks.

Common and Newton black films, which are the ultimate stage of thinning of soap films, are investigated by absolute x-ray reflectivity. The challenging and open problem concerning these two systems is the determination of the equilibrium thickness of the aqueous core. X-ray reflectivity provides very detailed and new information about their sandwich structure: The Newton black film appears much thinner than expected. As opposed to the common black film, it does not contain any aqueous core but only a hydration layer. In both cases the amphiphilic structure is the same.

A new time-resolved x-ray method of probing the kinetics of interfacial strains in semiconductor heterostructures is presented. High-resolution synchrotron-radiation measurements of the strain relaxation during rapid thermal annealing show that the lattice dilation of an as-grown quantum-well structure is relieved cooperatively by a series of sluggish discontinuous transitions. Well-defined metastable states of strain are observed between the transitions.

We discuss a model for the growth of interfaces relaxing by surface diffusion. We show that thermal noise can produce novel large-scale orientational fluctuations in the active zone of the growth. The resulting growth morphology is related to the structure of membranes and cannot be described by existing theories of self-affine growth.

We study a new model for kinetic growth motivated by the physics of molecular-beam epitaxy where the deposited atoms can relax to kink sites maximizing the number of saturated bonds. The model is thus intermediate between the well-known random-deposition model with no relaxation and the random-deposition model with perfect relaxation, producing growth exponents which are in between these two extremes. In particular, the growth exponent β, defining the interface width W∼${\mathit{t}}^{\mathrm{\beta }}$ at intermediate times, is found to be β≊0.375±0.005 in d=1+1 dimensions. Our estimated α for this model is around 1.5 for 1+1 dimensions.

We report the first observation of quantized circulation in superfluid ${}_{}{}^3{}_{}{}^{}\mathit{B}$. The apparatus consists of a straight vibrating wire immersed in liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, which is cooled by a rotating nuclear demagnetization cryostat. The experiment is carried out at about 250 μK. The superfluid at this temperature is in the ballistic quasiparticle regime. Circulation around the wire is found to be stable only when it takes on the values -h/2${\mathit{m}}_3$, 0, and +h/2${\mathit{m}}_3$, where h is Planck’s constant and ${\mathit{m}}_3$ is the mass of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ atom. This experiment confirms that superfluid ${}_{}{}^3{}_{}{}^{}\mathit{B}$ is a Cooper-paired superfluid with a macroscopic quantum wave function.

The electronic structures are calculated for several crystalline approximants of quasicrystals, AlCuLi and AlFe. The densities of states of these systems, and also of AlMn, suggest universality of the pseudogap at the Fermi energy in quasicrystals. The pseudogap satisfies a Hume-Rothery–type relation. The origin of the pseudogap is attributed to strong electron scattering by the lattice and the pseudogap causes an enhancement of cohesive energies. The characteristics of the states in the pseudogap and the electric resistivity are also discussed.

We report He-atom time-of-flight measurements and microscopic calculations of surface-phonon spectral densities and dispersion curves, revealing the presence of ‘‘anomalous’’ resonances in the phonon spectrum for low-index surfaces of Al. These resonances are similar to those observed in d-electron metals, for which they have been attributed to sp-d hybridization effects. For sp-bonded Al the resonances are not related to a ‘‘softening’’ of a single force constant, but rather to cumulative effects of changes in the entire surface force field.

Six distinct orientations of hcp titanium have been grown as high-quality single crystals by molecular-beam epitaxy. The substrates were freshly grown bcc metals on sapphire. We identify four different nucleation mechanisms that compete to select the eventual crystal orientation. In one novel case, the growth of tilted Ti(101¯2) is identified with nucleation at step edges rather than on terraces of the stepped Ta(211) substrate.