A new kind of rigidity towards uncompensated spin in the spin-singlet ground state is considered. This spin rigidity is a generalization of the quantum-Hall-effect state incompressibility to the spin problem. The phenomenological Landau-Ginzburg theory is presented, and vortexlike properties of spin quasiparticles and the spectrum of the spin collective mode are considered.

Using a nonperturbative self-energy solution for the nondegenerate Anderson model, we calculate the temperature-dependent spectral-density function in the symmetric limit The function is found to give reliable results for all values of the parameter u and inverse temperature β.

Neutron-scattering and resistivity experiments on single crystals of ${\mathrm{La}}_{1.95}$${\mathrm{Ba}}_{0.05}$${\mathrm{CuO}}_4$ are described. On warming to as high as 250 K, the correlation length does not change, and the temperature dependence of the generalized susceptibility χ(Q,ω) is due solely to the temperature-dependence of the local response. We show that the associated relaxation rate in the metallic regime is ħΓ≃1/2${\mathit{k}}_{\mathit{B}}$T, in accord with the marginal-Fermi-liquid hypothesis, and relate our results to nuclear spin-lattice relaxation data.

1/f noise measurements have been performed on ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ single crystals with distinct resistivity characteristics. The noise spectral density is found to be several orders of magnitude larger than that of metals, with a temperature dependence that is independent of the resistivity. In the superconducting-transition region, we do not observe anomalously enhanced 1/f noise. We discuss the important role played by the crystal morphology and we present a tunneling model which explains the experimental data quantitatively.

Using results from previous work on a spin-polaron model of high-${\mathit{T}}_{\mathit{c}}$ superconductivity, together with a hole-filling mechanism, excellent agreement with experimental data for ${\mathit{T}}_{\mathit{c}}$ in Y-Ba-Cu-O and Pr-Ba-Cu-O alloys and layered structures is obtained without introducing either pair breaking by the Pr ions or pairing interactions between unit cells.

We conside the kinetics near a first-order poisoning transition for simple surface reaction models which exlude nonreactive desorption. Elucidation of the development and growth of the reactive steady state from a near-poisoned state is achieved via an ‘‘oxidation epidemic’’ analysis of the evolution of an empy patch embedded in the poisoned phase. Associated critical exponents vary strongly with reaction rate, and reflect slow kinetics. The increase in epidemic survival probability with initial patch size is smooth, and described by additional exponents, rather than indicating a critical size for survival.

The semiclassical two-anyon partition function is shown to give the exact answer for the quantum second virial coefficient of an anyonic gas. The same method, when extended to the semiclassical three-anyon partition function, yields a remarkably simple result. The implications and the limitations of the method are pointed out.

Quasienergy eigenstates are constructed for a quantum harmonic oscillator with a periodic, time-dependent ‘‘spring constant.’’ This is done by a sequence of canonical transformations. The wave function in the new variables is that of an ordinary oscillator.

We present a new cluster-update Monte Carlo algorithm for a fluctuating interface in the 3D Ising model. Critical slowing down is drastically reduced and the dynamical critical exponent at the roughening temperature of the 3D Ising model is found to be ${\mathit{z}}_{\mathrm{cl}}$=0.44±0.03. For the Metropolis algorithm we obtain ${\mathit{z}}_{\mathrm{Met}}$=2.0±0.1 while the Swendsen-Wang algorithm performs even worse than local updating. A new method which suppresses fluctuations in the two bulk phases is introduced to determine moments of the interfacial thickness.

The scaling dimensions and the asymptotic behavior of correlation functions of the main operators in a continuous model of a spinless 1D Bose or Fermi gas with a rather general pairwise interaction are obtained using finite-size effects.

Recent searches for multiple quasistellar-object images created by gravitational lensing provide new limits on the density of massive compact objects in the Universe. These limits imply that the cosmological density of compact objects more massive than ${10}^{9.9}$${\mathit{M}}_{\mathrm{\odot }}$ must be less than closure density, and that the density of compact objects more massive than ${10}^{10.3}$${\mathit{M}}_{\mathrm{\odot }}$ must be less than 0.25 of the closure density.

The Universe may be critically closed by baryons and not conflict with standard big-band nucleosynthesis if the comoving number density of photons is reduced after nucleosynthesis. This is accomplished at a temperature of order 10 keV by recoupling the photons to a cold hidden sector via a photon-mixing mechanism. Signatures from supernovae, neutrino backgrounds, and nucleosynthesis are discussed.

We propose an ansatz for a low-energy effective action S¯ for a gravity-plus-matter system which is given by the usual action S (integral over space-time) divided by the space-time volume, S¯=S/V. The resulting gravitational equation is independent of the value of the cosmological constant that is present in S. We suggest that S¯ can be considered as an approximation for the effective action in the ‘‘duality-symmetric’’ closed-string theory in which the string coordinates x and their ‘‘duals’’ x̃ are treated as independent.

An extended-soliton solution to the low-energy heterotic-field-theory equations of motion is constructed from an eight-dimensional octonionic instanton. The soliton describes a string in ten-dimensional Minkowski space, and preserves only one of the sixteen spacetime supersymmetries.

We consider a self-dual SU(N) non-Abelian Chern-Simons theory with a scalar field in the fundamental representation. We study nontopological solitons in symmetric and asymmetric phases and show that they are at the threshold of stability against emission of elementary particles.

We propose an extension of the dynamical electroweak-symmetry-breaking scheme via top-quark condensate where b-quark and τ-lepton masses arise at low energies as one-loop radiative corrections out of the top quark. Corresponding to the compositeness scale Λ=${10}^{15}$–${10}^6$ GeV, the top-quark mass is predicted to be ${\mathit{m}}_{\mathit{t}}$=159–200 GeV, in good agreement with the electroweak ρ parameter.

The ratio R(S)=${\mathrm{\sigma }}_{\mathrm{tot}}$(${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$→hadrons)/σ(${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$→${\mathrm{\mu }}^{+}$${\mathrm{\mu }}^{\mathrm{-}}$) is calculated to the four-loop level in perturbative QCD. The result differs from a previous calculation and is much smaller. In addition, a new result for the four-loop β function in QED is obtained. This result also disagrees with a previous calculation.

We examine the deuteron properties using the new value for the πNN coupling constant, ${\mathit{g}}_{\mathrm{\pi }}^2$/4π=13.3±0.3, which has been obtained in a recent analysis of ${\mathrm{\pi }}^{\pm }$p data and is about 7% smaller than earlier determinations. We find that this value is at variance with the deuteron properties if the strong empirical (Höhler-Pietarinen) ρ coupling is assumed which, in fact, is used in almost all modern realistic meson-theoretic models for the NN interaction. Within such models, a minimum of 13.9 for ${\mathit{g}}_{\mathrm{\pi }}^2$/4π is required, especially for the correct description of the deuteron quadrupole moment.

Absolute total and differential cross sections for the reaction ${\mathrm{\pi }}^{+}$+d→p+p have been measured for pion energies from 3.7 to 20.5 MeV. Evidence for p-wave strength was observed for all energies. Using detailed balance and corrections for Coulomb effects, the measured differential and total cross sections were found to be consistent with recent measurements for the reaction n+p→d+${\mathrm{\pi }}^0$, offering no evidence for charge-independence breaking. The measured total cross sections for energies below 30 MeV are in disagreement with predictions by Blankleider and by Vogelzang, Bakker, and Boersma.

We compare the elastic-scattering cross sections for electrons and positrons from ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. The results demonstrate that the electron-nucleus interaction can be described to good accuracy as a single hard-photon exchange process, and validate the theoretical framework used to interpret electron-scattering data in terms of ground-state charge densities of nuclei.