We present a theory for the effect of interlayer coupling in a superlattice on the magnetoroton modes of a two-dimensional electron gas in a strong magnetic field. We find that for typical fields and layer spacings the modes broaden into bands. For sufficiently small layer spacings, the gap necessary for the occurrence of the fractional quantum Hall effect vanishes. We argue that the vanishing of the gap should be associated with an instability toward the state with a two-dimensional Wigner crystal in each layer and that this state is favored by interlayer coupling.

The differential resistance of ${\mathrm{NbSe}}_3$ measured in the presence of combined ac and dc electric fields exhibits interference features. Our experimental results for the dependence of these features on ac amplitude and frequency are in complete and dramatic disagreement with predictions of the classical model of deformable charge-density waves, and prove that pinning by impurities does not vanish at large fields and frequencies.

We have observed coupling between excited and ground states of excitons in GaAs quantum wells under an electric field. Low-temperature photoluminescence excitation spectra show peaks corresponding to excited states of the heavy-hole exciton and to the ground state of the light-hole exciton. With increasing field, the peaks converge and then they show anticrossing and share their oscillator strengths. As a result of this interaction, fine structure attributed to the 2p state of the heavy-hole exciton is resolved.

Computationally efficient discrete space-time models of phase-ordering dynamics of thermodynamically unstable systems (e.g., spinodal decomposition) are proposed. Two-dimensional lattice (100×100) simulations were performed to obtain scaled form factors.

In the past the universal features of the breakup of the last Kolmogorov-Arnol’d-Moser (KAM) torus has been studied by use of renormalization theory. In this case, the renormalization equations converge to a fixed point representing a map with nonsmooth noble circle. The work described in this paper strongly suggests that the breakup of any KAM torus with arbitrary winding number can be described by chaotic renormalization equations which converge on a strange attractor. The properties of this attractor are global scaling exponents characterizing the breakup of almost all KAM tori. This work unifies the quasiperiodic transitions to chaos in Hamiltonian and dissipative systems.

We show that in a model obtained by addition of N minimally coupled massless fermions to the original ${\mathrm{CP}}^{\mathrm{N}\mathrm{-}1}$ model, one obtains asymptotic states belonging to the fundamental representation of U(N). We view these states as liberated fundamental ${\mathrm{CP}}^{\mathrm{N}\mathrm{-}1}$ solitons. They have an S matrix whose factorizability was verified to order 1/${\mathrm{N}}^2$ and whose scattering amplitudes coincide to order 1/N with a previously computed exact S matrix without bound states. All fermionic degrees of freedom except one decouple from the physical Hilbert space.

An explicit construction of closed-string states is given in terms of open-string oscillators acting on the open-string Fock vacuum. The closed-open-open coupling is computed for the graviton and agrees with the standard result. The closed string states are not annihilated by the Becchi-Rouet-Stora-Tyutin operator Q. Instead they generate inner derivations which anticommute with Q. This is sufficient to insure gauge invariance of tree-level S-matrix elements. It also implies that the closed-string states obey, level by level, the linearized equation of motion of the cubic action.

One-loop corrections to δρ=(${\mathrm{m}}_{\mathrm{W}}$/${\mathrm{m}}_{\mathrm{Z}}$cos${\mathrm{theta}}_{\mathrm{W}}$${)}^2$-1 are evaluated in technicolor theories which have pseudo-Goldstone bosons. The experimental bound δρ≤0.02 requires that 〈Q¯Q〉, the technicolor chiral condensate, be bounded from above. In theories where techniquarks carry ordinary color, and the isospin violation in the extended technicolor sector is ∼(${\mathrm{m}}_{\mathrm{c}}$-${\mathrm{m}}_{\mathrm{s}}$)/(${\mathrm{m}}_{\mathrm{c}}$+${\mathrm{m}}_{\mathrm{s}}$)∼1, this bound is 〈Q¯Q〉≤(2.3 TeV${)}^3$. This places interesting constraints on the masses of ordinary fermions and color-singlet pseudo-Goldstone bosons.

The weak coupling constants of the electron, $g_V^e$ and $g_A^e$, are determined from measurements of the total and differential cross sections for the reaction ${\nu }_{\mu }$e→${\nu }_{\mu }$e. The data also place limits of interest on the magnitudes of a neutrino charge radius and a possible neutrino magnetic dipole moment.

We have measured the mean lifetime of the hadrons containing b quarks that are produced in $e^{+}$$e^{\mathrm{-}}$ annihilation at √s =29 GeV. We use the full sample of data collected by the MAC detector at the SLAC storage ring, PEP, including those recently acquired with a precision vertex detector. The result is ${\tau }_b$=[1.29±0.20(stat) ±0.07(syst) ps]×(1.00±0.15), where the last factor is the systematic uncertainty in the scale.

Inclusive ${\Xi }^{\mathrm{-}}$ production in $e^{+}$$e^{\mathrm{-}}$ annihilation at 29 GeV has been measured with the Mark II detector. From an integrated luminosity of 207 ${\mathrm{pb}}^{\mathrm{-}1}$, we determine a production rate of 0.017±0.004±0.004 ${\Xi }^{\mathrm{-}}$+Ξ${¯}^{+}$ per hadronic event. A search for ${\Xi }^{\mathrm{*}0}$(1530)→${\Xi }^{\mathrm{-}}$${\pi }^{+}$ leads to an upper limit of N(${\Xi }^{\mathrm{*}0}$)/N(${\Xi }^{\mathrm{-}}$)<0.35 at a 90% confidence level.

The real part of the isospin-even forward-scattering amplitude of pion-nucleon scattering has been determined at a pion energy of $T_{\pi }$=55 MeV by measurement of the elastic scattering of positive and negative pions on protons within the Coulomb-nuclear interference region. The value confirms the prediction of the Karlsruhe-Helsinki phase-shift analysis for that energy. These phases have been used to determine the σ term of pion-nucleon scattering by means of dispersion relations, resulting in a value for σ which is in contradiction with chiral perturbation theory of QCD.

We consider the quantum mechanics of the SU(2) skyrmion model in the framework of collective-coordinate quantization. We treat the Lagrangean quantum-mechanically from the beginning. A new mass term with negative sign appears, which may play an important role in stabilizing the rotating chiral soliton.

We present a bosonic realization of the SU(2)×SU(2) algebra of the skyrmion. By imbedding the algebra in U(4), we introduce an additional quantum number N, which we identify with the number of colors, ${\mathrm{N}}_{\mathrm{c}}$. We show that the skyrmion is a coherent state of the U(4) algebra in the large-N limit and generalize that state of finite N. For N=${\mathrm{N}}_{\mathrm{c}}$=3, we recover the SU(4) quark model. The algebraic 1/${\mathrm{N}}_{\mathrm{c}}$ corrections to one-body matrix elements in the skyrmion are discussed.

A universal, physically intuitive description of collectivity in heavy nuclei is obtained in terms of the parameter P=$N_p$$N_n$/($N_p$+$N_n$) which gives the average number of interactions of each valence nucleon with those of the other type. Regardless of mass region, deformation sets in when P=$P_{\mathrm{crit}\mathrm{\approxeq }4–}$5. This, in turn, gives a rule that medium-mass and heavy nuclei with effective $N_p$ or $N_n$≤4 cannot be deformed. An interpretation in terms of the monopole and quadrupole p-n interactions is discussed.

The structure of the very neutron-deficient Ge region has been investigated with use of particle-γ coincidence techniques in weak fusion-evaporation channels. Excited states up to spin (31/2) have been established in ${}_{}{}^{65}{}_{}{}^{}\mathrm{Ge}$, and five transitions have been assigned to the N=Z nucleus ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ge}$. The first excited state in ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ge}$ is at 902.1±0.8 keV. The ${}_{}{}^{65}{}_{}{}^{}\mathrm{Ge}$ level scheme provides the first indication in this mass region of a theoretically predicted softness with respect to octupole deformation.

The radiative decay of Cs atoms excited into the 5${\mathrm{D}}_{5/2}$ level and passing between two metallic mirrors spaced by a 1.1-μm gap is observed to depend upon their angular momentum. Spontaneous emission at a wavelength of 3.49 μm is suppressed for the substates with maximum angular momentum normal to the mirrors, which survive without substantial decay during ∼13 natural lifetimes. The radiation rate is modified by application of a magnetic field which mixes sublevels having lifetimes in the gap. This experiment illustrates the anisotropy of the vacuum field in confined space.

A method is given for analytic determination of new stationary configurations of objects with logarithmic pair potentials in two dimensions such as vortices, charges, and screw dislocations. The method is applicable to configurations with arbitrary mixed strengths in the presence of background fields. New stationary and uniformly translating vortex configurations are presented, some of which can be generated from N-soliton solutions of the Korteweg–de Vries equation.

Light-scattering measurements were made in a binary mixture in the late stage of spinodal decomposition, when gravity has become important. We observe macroscopic flow in the mixture, following which the scattering I(k,t) falls as $k^{\mathrm{-}4}$. This implies that the scattering is mainly from surfaces between growing domains. The measurements reveal an unexpectedly large rate of disappearance of the surface area per unit volume in the phase-separating system. The effect is probably related to a gravity-driven instability which gives rise to the flow and which was also investigated.

We report measurements on a new collective spin-wave mode trapped by the textural boundary layers of ${}_{}{}^3{}_{}{}^{}\mathit{A}$ within a stack of thin Mylar plates. The surface mode was seen as a new peak in the cw NMR spectrum measured at $H_0$=284 Oe. Rotation of the sample, with Ω orthogonal to the gaps, increased the spectral weight of the surface mode, indicating an increase in the textural boundary layers caused by a counterflow-induced transition. This phenomenon was used to study vortex creation and persistent currents.