The in-plane resistivity ${\mathrm{\rho }}_{\mathit{a}\mathit{b}}$(T) and Hall coefficient ${\mathit{R}}_{\mathit{H}}$(T) have been measured for ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{y}}$ single crystals with various oxygen concentrations. We find that for oxygen-depleted samples ${\mathrm{\rho }}_{\mathit{a}\mathit{b}}$(T) deviates from T-linear behavior and that ${\mathit{R}}_{\mathit{H}}$(T) deviates from 1/T below a temperature ${\mathit{T}}_{\mathit{o}}$ well above ${\mathit{T}}_{\mathit{c}}$. The deviation coincides with the development of a gap in the spin excitations seen in recent neutron and NMR studies. This is evidence that the charge transport in the ${\mathrm{CuO}}_2$ plane is determined by spin scattering.

A miniature superconducting resonator operating at 1.3 K and 900 MHz has been used to measure the change in λ(T) from 1.3 K to ${\mathit{T}}_{\mathit{c}}$ in very high quality single crystals of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.95}$. The data, which have a resolution of 1-2 Å, show a strong linear term extending from approximately 3 to 25 K. We believe the strong linear dependence to be characteristic of the pure system and that its apparent absence in thin films and some crystals is due to the presence of defects.

Inelastic neutron scattering has been used to study the temperature dependence of the magnetic response in the one-dimensional S=1/2 Heisenberg antiferromagnet ${\mathrm{KCuF}}_3$. The scattering is consistent with that expected for unbound spinon pair excitations.

We give a procedure for a renormalized perturbation expansion. It is demonstrated for the Anderson impurity model, but has wide potential application. To zero order it describes the Landau noninteracting quasiparticles. To first order in the renormalized interaction Ũ it gives the exact thermodynamic results for low temperatures, and to second order gives the exact ${\mathit{T}}^2$ coefficient for the resistivity. The approach is not restricted to the Fermi liquid regime and provides a framework for systematic corrections to Fermi liquid theory.

We examine a model of M-component quantum rotors coupled by Gaussian-distributed random, infinite-range exchange interactions. A complete solution is obtained at M=∞ in the spin-glass and quantum-disordered phases. The quantum phase transition separating them is found to possess logarithmic violations of scaling, with no further modifications to the leading critical behavior at any order in 1/M; this suggests that the critical properties of the transverse-field Ising model (believed to be identical to the M→1 limit) are the same as those of the M=∞ quantum rotors.

The complex dielectric constant of ${\mathrm{Rb}}_{0.40}$(${\mathrm{ND}}_4$${)}_{0.60}$${\mathrm{D}}_2$${\mathrm{PO}}_4$ has been measured in the frequency interval from 1 mHz to 1 GHz at temperatures between 40 and 140 K. A novel frequency-temperature plot of the data is introduced to show that the behavior of the relaxation spectrum is reflected in the real part of the dielectric constant. It is found that the highest relaxation frequency ${\mathit{f}}_2$=1/2π${\mathrm{\tau }}_{\min }$ follows an Arrhenius behavior, whereas the lowest frequency ${\mathit{f}}_1$=1/2π${\mathrm{\tau }}_{\max }$ exhibits a critical decay according to the Vogel-Fulcher law ${\mathit{f}}_1$∝exp[-U/(T-${\mathit{T}}_0$)] with ${\mathit{T}}_0$=32.9 K.

The electronic band structure of Al and Si in the region temporarily collisionally perturbed by impact of low energy particles was calculated using the large-unit-cell-pseudopotential method. Kinetic energies in collisions were assumed to be far below the core excitation threshold. The results of the calculation show that localized levels are transiently formed in the perturbed region with energies up to several electronvolts below the valence bands. Electronic excitations of these levels can significantly influence electron and ion emissions from bombarded solids.

We obtain an exact time dependent solution of the zero temperature Kawasaki-type dynamics of a phase separation model on the Bethe lattice with arbitrary coordination number. We also do a direct numerical simulation and show an excellent match between the analytical and numerical results. The nonergodic dynamics leads to a frozen final state whose structure depends crucially on the inititial conditions.

Point masses moving in 2+1 dimensions draw out braids in space-time. If they move under the influence of some pairwise potential, what braid types are possible? By starting with fictional paths of the desired topology and ‘‘relaxing’’ them by minimizing the action, we explore the braid types of potentials of the form V∝${\mathit{r}}^{\mathrm{\alpha }}$ from α≤-2, where all braid types occur, to α=2, where the system is integrable. We also discuss issues of symmetry and stability. We propose this kind of topological classification as a tool for extending the ‘‘symbolic dynamics’’ approach to many-body dynamics.

Hawking’s radiance departs from blackbody form due to the mode dependence of the barrier penetration factors. Thus it is not the maximal entropy radiation for given energy. To check whether this entropic deficiency is consistent with the possibility that the radiance may carry information about the quantum state in the far past, we compare estimates of the actual entropy emission rate with the maximal possible one for the same power. Standard quantum communication theory then shows that the permitted information outflow rate can be as large as the rate of black hole entropy decrease. The initial information may thus gradually leak out during the evaporation.

A general formula for the entropy of stationary black holes in Lovelock higher-curvature gravity theories is obtained by integrating the first law of black hole mechanics, which is derived by Hamiltonian methods. The entropy is not simply one quarter of the surface area of the horizon, but also includes a sum of intrinsic curvature invariants integrated over a cross section of the horizon.

A new framework is found for the compactification of supersymmetric string theory. It is shown that the massless spectra of critical string vacua with central charge c=3${\mathit{D}}_{\mathrm{crit}}$ can be derived from manifolds of complex dimension ${\mathit{D}}_{\mathrm{crit}}$+2(Q-1),Q≥1, whose first Chern class is quantized in a particular way. This new class is more general than that of Calabi-Yau manifolds because it contains spaces corresponding to vacua with no Kähler deformations, i.e., no antigenerations, thus providing mirrors of rigid Calabi-Yau manifolds. The constructions introduced here lead to new insights into the relation between Landau-Ginzburg vacua on the one hand and Calabi-Yau manifolds on the other.

The type II superstring amplitude to 1-loop order is given by an integral of ϑ functions over the moduli space of tori, which diverges for real momenta. We construct the analytic continuation which renders this amplitude well defined and finite, and we find the expected poles and cuts in the complex momentum plane.

It is shown that in the physically interesting domain of the parameter space of SU(5) supergravity grand unified theory, the Higgs-boson and Z poles dominate the annihilation of the lightest supersymmetric particle. Here the naive analyses on thermal averaging breaks down and formulas are derived which give a rigorous treatment over the poles. These results are then used to show that there exist significant domains in the parameter space where the constraints of proton stability and cosmology are simultaneously satisifed. New upper limits on light particle masses are obtained.

A limit on the tau neutrino mass ${\mathit{M}}_{\nu \mathrm{\tau }}$ is obtained from a study of tau decays in the reaction ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$→${\mathrm{\tau }}^{+}$${\mathrm{\tau }}^{\mathrm{-}}$ at center-of-mass energies ∼10.6 GeV. The result is based on an end-point analysis of the invariant mass spectrum of the decay products in the decay modes ${\mathrm{\tau }}^{\mathrm{-}}$→3${\mathit{h}}^{\mathrm{-}}$2${\mathit{h}}^{+}$${\nu }_{\mathrm{\tau }}$ and ${\mathrm{\tau }}^{\mathrm{-}}$→2${\mathit{h}}^{\mathrm{-}}$${\mathit{h}}^{+}$2${\mathrm{\pi }}^0$${\nu }_{\mathrm{\tau }}$. The data sample used in this analysis contains 1.77×${10}^6$ tau pairs, corresponding to an integrated luminosity of 1.92 ${\mathrm{fb}}^{\mathrm{-}1}$, and is substantially larger than previous data samples used to place a limit on ${\mathit{M}}_{\nu \mathrm{\tau }}$. The limit obtained for both five-hadron modes together is 32.6 MeV at 95% C.L.

We have measured two-fragment reduced-velocity correlation functions of the intermediate mass fragments (IMF: 3≤Z≤7) produced in multifragment final states for the Kr+Nb system (E/A=35, 45, 55, 65, and 75 MeV). From the measured correlation functions we extract mean IMF emission lifetimes (τ) which are observed to decrease from τ≊400 fm/c at E/A=35 MeV to τ≊125 fm/c at E/A=55 MeV. For beam energies in excess of E/A=55 MeV, no further decrease in τ is observed, indicating a possible saturation of the mean emission lifetime for IMF produced in multifragment exit channels.

The momentum dependence of the two-proton correlation function is studied for central and peripheral ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$${+}^{45}$Sc collisions at E/A=80 MeV. Calculations with the Boltzmann-Uehling-Uhlenbeck transport theory reproduce well the measured momentum dependence of the correlation functions for central collisions, but underpredict the momentum dependence for peripheral collisions.

We report the first observation of hyperfine splitting on an x-ray laser transition. Hyperfine splitting can have a major impact on laser gain and help explain anomalous behavior and poor performance of x-ray lasers with odd Z. In our experiments we measure the line shape of the J=0→1, 3p→3s transition in Ne-like Nb and Zr and observe a 28 mÅ splitting between the two largest hyperfine components in the Nb (Z=41) line at 145.9 Å, in good agreement with theory. As predicted, no splitting is observed in Zr (Z=40).

The angular dependence of the spin polarization of Auger electrons was measured after 5p photoionization of free Ba atoms with circularly polarized light. A substantial polarization transfer from the oriented photoion onto the Auger electrons was observed in confirmation of theoretical predictions by Kabachnik and Lee. The ratio of the dipole transition matrix elements and the orientation and alignment coefficients were extracted from the experimental data for the Auger electron polarization parameters.

Gamma rays and, for the first time, conversion muons of pt fusion have been measured from liquid mixtures of protium, deuterium, and tritium. The rate ${\lambda }_{10}$ for spin flip from the triplet to the singlet state of tμ(1s) was found to be ${\lambda }_{10}$=(1.06±0.13)×${10}^3$μ${\mathit{s}}^{\mathrm{-}1}$, the rate for muon-catalyzed pt fusion from the (I=1) nuclear-spin state to be ${\lambda }_{\mathit{p}\mathit{t}}^{\mathit{f}}$(I=1) =0.067±0.${002}_{\mathrm{-}0.002}^{+0.005\mathrm{}}$μ${\mathit{s}}^{\mathrm{-}1}$, and the and the molecular formation rate to be ${\lambda }_{\mathit{p}\mathit{t}}^{\mathit{m}}$=(7.5±0.$3_{\mathrm{-}0.3}^{+1.0\mathrm{}}$)μ${\mathit{s}}^{\mathrm{-}1}$ (all rates normalized to liquid hydrogen density).