We analyze the effect of irregular classical scattering on the corresponding quantum-mechanical scattering matrix. Using semiclassical arguments, we show that the fluctuations in the S matrix and the cross sections are consistent with a random-matrix description (Ericson fluctuations). The results are illustrated by a numerical solution of a simple quantum problem, whose classical counterpart displays irregular scattering.

We investigate the problem of inequivalent quantizations of a physical system with multiply connected configuration space X. For scalar quantum theory on X we show that state vectors must be single valued if and only if the first homology group ${\mathrm{H}}_1$(X) is trivial, or equivalently the fundamental group ${\mathrm{\pi }}_1$(X) is perfect. The θ structure of quantum gauge and gravitational theories is discussed in light of this result.

The N-point functions for the p-adic version of the bosonic open-string theory are derived and discussed. The cases N=5 and 6 are explicitly calculated, and lead to simple (factorizable) formulas from which the general N case can be formulated.

The four-dimensional ${\mathrm{Z}}_2$ gauge theory is studied by Monte Carlo renormalization-group methods. The renormalization-group flows are discontinuous at the first-order phase-transition point and are not associated with a discontinuity fixed point. Evidence for critical fixed points within the metastable regions is presented.

Quantum chromodynamics at finite temperature and chemical potential is investigated nonperturbatively at large distance scales in terms of its three-dimensional effective theory, which for the gauge group SU(2) is the Georgi-Glashow-Polyakov model. It is shown that a global SU(2) symmetry breaks if the temperature is high enough and it is argued that this new transition most likely coincides with deconfinement. Some implications for quark-gluon-plasma physics are discussed.

Six years ago, a gauge model of generation nonuniversality was proposed in which the τ lifetime was predicted to be longer, and $B^0$-B${¯}^0$ mixing to be greater, than in the standard model. Since current experimental data appear to favor both of these interpretations, an updated and improved analysis is here presented. In particular, a plausible branching fraction of the order ${10}^{\mathrm{-}4}$ is predicted for b→${\mathrm{sl}}^{+}$$l^{\mathrm{-}}$, just below the present experimental limit and well above the standard-model expectation of ${10}^{\mathrm{-}6}$.

A remeasurement of the β-decay asymmetry parameter for ${}_{}{}^{35}{}_{}{}^{}\mathrm{Ar}$ decay to the ground state of ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$ has been performed. The result, $A_0$=0.49±0.10, leads to a value for the quark mixing angle ${\theta }_C$=0.28±0.08 rad, in agreement with the accepted value 0.23±0.01 and in strong disagreement with the anomalous result ${\theta }_C$<0.10 (95% confidence level) determined from previous measurements of this asymmetry parameter.

A rotational band of nineteen transitions, extending to spin∼(127/2ħ and with an average moment of inertia ${\mathrm{scrI}}^{\mathrm{}\left(2\right)\mathrm{}}$ of 77 ${ħ}^2$ ${\mathrm{MeV}}^{\mathrm{-}1}$, has been observed in ${}_{}{}^{149}{}_{}{}^{}\mathrm{Gd}$. Its intensity accounts for approximately (1/2% of the total fusion cross section. Lifetime measurements yielded an average quadrupole moment of 17±2 e-b, in excellent agreement with the value calculated microscopically for a superdeformed shape. The trends in ${\mathrm{scrI}}^{\mathrm{}\left(1\right)\mathrm{}}$ and ${\mathrm{scrI}}^{\mathrm{}\left(2\right)\mathrm{}}$ are consistent with very weak pairing effects. The data also suggest that to populate superdeformed bands significantly one must form cold residual nuclei.

The recently discovered radioactive decay of heavy nuclei by emission of carbon and neon is described by a model containing elements from both the theory of α decay and that of fission. A key ingredient is the inertial mass, which depends on the superfluid pairing gap of the nucleus. The potential energy is estimated from macroscopic considerations. Theory and experiment fit together in a reasonable way to give an overall picture of exotic decay.

Motivated by recent experiments, a series of molecular-dynamics simulations of ions confined in a Penning trap have been performed. The temperature T and the density ${\mathrm{n}}_0$ are such that the correlation parameter Γ is large (Γ=${\mathrm{e}}^2$/akT, where 4π${\mathrm{a}}^3$/3=${\mathrm{n}}_0$). However, because of the relatively small size of the ion cloud, results differ considerably from previous studies of unbounded systems. The ions form concentric spheroidal shells, but diffuse freely on the shells. As Γ increases, diffusion decreases and a distorted 2D hexagonal lattice forms on the outer shells.

We report the first observation of Bragg scattering of sodium atoms from a standing light wave. We also present a theory which quantitatively predicts the amplitude of the various Bragg orders as a function of the light’s detuning and power, and the interaction time. The analog of the Pendello$uml—sung effect, previously observed in Bragg scattering of neutrons from crystals, is predicted and qualitatively observed for first-order Bragg scattering of atoms from a standing light wave.

We report observation of dynamical resonances in the reaction H+${\mathrm{H}}_2$(v=0,j=0.2)→${\mathrm{H}}_2$(v’,j’)+H. The reactive cross section as a function of v’ and j’ is determined under single-collision conditions for 22 total energies between 0.95 and 1.37 eV. Resonances appear as sharp increases in the v’=1 cross section at 0.97, 1.20, and 1.26 eV, and possibly 1.11 eV. These energies are in excellent agreement with the energies of theoretically predicted Feshbach resonances in the reaction.

The ideal MHD linear stability theory of arbitrary-n (including n=1) interchange modes in shaped tokamaks with flat central rotational transform is developed. The unstable modes have very long parallel wavelength everywhere, but their perpendicular wavelength is assumed to be comparable to the plasma minor radius. It is shown that the stability condition against these radially extended modes is independent of their toroidal wave number n, and identical to the shearless limit of the n≫1 Mercier criterion.

The problems of a directed polymer in a random matrix, a randomly stirred fluid obeying Burger’s equation, and the dynamics of an interface growing by vapor deposition can be mapped into each other. Renormalization-group arguments suggest that there is an upper critical dimension for these systems above which the correlation length exponent ν should be (1/2. We present an argument which suggests that ν=(2/3 in all dimensions (that is, it is superuniversal), in agreement with the conjecture and numerical simulations of Kardar and Zhang.

The ‘‘valence-bond’’ ground states for extended Heisenberg models discussed by Affleck et al. are shown to be of a Jastrow form. We discuss a striking analogy between these models and the ‘‘truncated pseudopotential’’ approach to the fractional quantum Hall effect. The valence-bond states are in analogy to the Laughlin ground state, and the magnon spectrum is deduced by use of a single-mode approximation.

Electronic transport through a three-dimensionally confined semiconductor quantum well (‘‘quantum dot’’) has been investigated. Fine structure observed in resonant tunneling through the quantum dot corresponds to the discrete density of states of a zero-dimensional system.

We observe positronium (Ps) emission from a graphite surface being bombarded by slow positrons. The band structure of graphite does not support the usual one-electron-hole process for Ps formation because of conservation of momentum parallel to the surface. A large temperature coefficient for the emission of energetic Ps suggests a new mechanism in which momentum conservation is satisfied by the emission and absorption of phonons. A simple theory including one-phonon processes explains the temperature dependence as well as the angular distribution of the Ps.

New measurements are reported on three La-Ba (and La-Sr) copper-oxide compounds, including one new compound. These materials have metallic conductivities, comparable to those of the high-$T_c$ copper oxides in the normal state, but they are not superconducting down to 5 K. Their magnetic susceptibility and structural features are also similar. These data provide a new challenge and test for the numerous theories of high $T_c$ to account also for its absence in these three closely related materials.

An explicit interaction-Hamiltonian realization of a measurement of the free-mass position with the following properties is given: (1) The probability distribution of the readouts is exactly the same as the free-mass position distribution just before the measurement. (2) The measurement leaves the free mass in a contractive state just after the measurement. It is shown that this measurement breaks the standard quantum limit for the free-mass position in the sense sharpened by the recent controversy.

We provide evidence for a new unitary series of conformal field theories, labeled by integers M and N. For N=1,2 they reproduce the unitary conformal and superconformal series of minimal models. For higher N, they correspond to models with c>1, generated by new nonlocal currents of spin (N+4)/(N+2). We use a generalization of the Feigin-Fuchs construction to find the currents and the primary fields of the new algebras.