The SU(n) quantum chains with inverse-square exchange exhibit a novel form of Yangian symmetry compatible with periodic boundary conditions, allowing states to be countable. We characterize the ‘‘supermultiplets’’ of the spectrum in terms of generalized ‘‘occupation numbers.’’ We embed the model in the k=1 SU(n) Kac-Moody algebra and obtain a new classification of the states of conformal field theory, adapted to particlelike elementary excitations obeying fractional statistics.

A first-order cosmological phase transition that proceeds through the nucleation and collision of true-vacuum bubbles is a potent source of gravitational radiation. Possibilities for such include first-order inflation, grand-unified-theory-symmetry breaking, and electroweak-symmetry breaking. We have calculated gravity-wave production from the collision of two scalar-field vacuum bubbles, and, using an approximation based upon these results, from the collision of 20 to 30 vacuum bubbles. We present estimates of the relic background of gravitational waves produced by a first-order phase transition; in general, ${\mathrm{\Omega }}_{\mathrm{GW}}$∼${10}^{\mathrm{-}9}$ and f∼(${10}^{\mathrm{-}6}$ Hz) (T/1 GeV).

We argue that CP is a gauge symmetry in string theory. As a consequence, CP cannot be explicitly broken either perturbatively or nonperturbatively; there can be no nonperturbative CP-violating parameters. String theory is thus an example of a theory where all θ angles arise due to spontaneous CP violation, and are in principle calculable.

We study a three-dimensional analog of the Wess-Zumino-Witten model, which describes the Goldstone bosons of three-dimensional quantum chromodynamics. The topologically nontrivial term of the action can also be viewed as a nonlinear realization of Chern-Simons form. We obtain the current algebra of this model by canonical methods. This is a three-dimensional generalization of the Kac-Moody algebra.

The existence of ultraheavy quanta too heavy to produce directly may be probed by means of the rising cross sections they would induce in scattering at the TeV energy scale of photon or gluon pairs to weak boson pairs, for instance γγ→ZZ or gg→ZZ.

We report a measurement of the ${\mathit{D}}^{\mathrm{*}+}$ and ${\mathit{D}}^{\mathrm{*}0}$ decay branching fractions based on 780 ${\mathrm{pb}}^{\mathrm{-}1}$ of data collected with the CLEO II detector. For radiative ${\mathit{D}}^{\mathrm{*}+}$ decay, we obtain an upper limit, scrB(${\mathit{D}}^{\mathrm{*}+}$→${\mathit{D}}^{+}$γ)<4.2% (90% confidence level), which is substantially below previous results, and eliminates the need for an anomalously large charm quark magnetic moment.

Using the decay modes, ${\mathit{D}}^{\mathrm{*}+}$→${\mathit{D}}^{+}$${\mathrm{\pi }}^0$ and ${\mathit{D}}^{\mathrm{*}0}$→${\mathit{D}}^0$${\mathrm{\pi }}^0$, we have measured the ${\mathit{D}}^{\mathrm{*}+\mathrm{-}}$${\mathit{D}}^{+}$ and ${\mathit{D}}^{\mathrm{*}0\mathrm{-}}$${\mathit{D}}^0$ mass differences to be 140±0.08±0.06 and 142.12±0.05±0.05 MeV, respectively. Combining these measurements with the Particle Data Group average for the ${\mathit{D}}^{\mathrm{*}+\mathrm{-}}$${\mathit{D}}^0$ mass difference, we obtain isospin mass splittings for ${\mathit{D}}^{\mathrm{*}+\mathrm{-}}$Dusp*0 and ${\mathit{D}}^{+\mathrm{-}}$${\mathit{D}}^0$ of 3.32±0.08±0.05 and 4.80±0.10 ±0.06 MeV. We discuss the implications of these measurements for models of isospin mass differences and model-dependent estimates of ${\mathit{f}}_{\mathit{D}}$.

A new method, use of a fragment separator as an energy-loss spectrometer, has been developed and used to make the first measurements of the parallel momentum distributions of ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ nuclei produced in the breakup of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$. Measurements were made for 66-MeV/nucleon ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ projectiles on ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$, and ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ targets. Distributions with Gaussian width of ${\mathrm{\sigma }}_{\mathrm{\parallel }}$≊19 MeV/c were observed for all targets—the first time such a narrow structure has been observed for medium and high mass targets. From the weak dependence of width on breakup target it appears that the paralell momentum distributions are relatively insensitive to the interaction governing the breakup and reflect an extended neutron distribution for ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$.

Cross section (σ), analyzing power (${\mathrm{A}}_{\mathrm{y}}$), induced polarization (P), and normal polarization transfer ${\mathrm{coefficientD}}_{\mathrm{N}{\mathrm{N}}^{\prime }}$) data have been measured for scattering of 200-MeV polarized protons from ${\mathrm{B}}^{10}$. Data for the $3^{+}$, T=0 to $0^{+}$, T=1 (1.74 MeV) isovector 0ħω stretched transition are compared to results of distorted-wave calculations. While σ, ${\mathrm{A}}_{\mathrm{y}}$, and P are reasonably described by calculations based on the free nucleon-nucleon(NN)t matrix, the ${\mathrm{D}}_{\mathrm{N}{\mathrm{N}}^{\prime }}$ data are not. The results suggest a larger transverse to longitudinal spin-dependent interaction ratio than is expected from free NN scattering. © 1992 The American Physical Society

The quadrupole moment of the ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ (${\mathit{I}}^{\mathrm{\pi }}$=$2^{+}$, ${\mathit{T}}_{1/2}$=769 msec) nucleus was measured as ‖Q${(}^8$B)‖=68.3±2.1 mb by use of modified β-NMR. This value is twice as large as the prediction of the Cohen-Kurath shell model. It is found by subtracting the contribution of deeply bound neutrons that the protons in ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ carry more than 90% of the observed moment. The anomalous value is accounted for fairly well by the proton halo due to the loosely bound valence configuration. This is the first experimental evidence for the existence of a proton halo covering a neutron core.

Enhanced population transfer from the lowest to the highest level in the three-state ladder 5s→5p→5d of the rubidium atom by frequency-swept ultrashort laser pulses is observed if the frequency sweep first makes the pulse resonant with the 5s→5p transition, and later with the 5p→5d transition. With this ‘‘intuitive’’ scheme it is possible to achive complete population inversion via the intermediate level by two successive adiabatic passages. Complete inversion is also obtained by a ‘‘counterintuitive’’ direction of the frequency sweep, in which case population of the intermediate level during the pulse is strongly reduced.

High-Rayleigh-number turbulent convection has been studied using the technique of photon-correlation homodyne spectroscopy to measure velocity differences at various length scales. The measured intensity correlation function G(q,t,L) is found to be of the scaling form G(qu(L)t), with u(L)∼${\mathit{L}}^{0.6}$ being the characteristic turbulent velocity at the legth scale L and q the scattering vector. It is also found that the lower cutoff length ${\mathit{l}}_{\mathit{c}}$ of the scaling range obeys a power law ${\mathit{l}}_{\mathit{c}}$∼${\mathrm{Ra}}^{\mathrm{-}0.3}$. The measured power-law exponents are in excellent agreement with theoretical predictions.

A fast penetration of a magnetic field into an initially homogeneous plasma is demonstrated. The penetration is induced by a density gradient along the current lines that is formed by the magnetic pressure in the two-dimensional flow. The penetration occurs for any magnitude of the plasma collisionality. If the collisionality is high enough the shock structure is determined by the resistivity, while in the low-collisionality case it is determined by the electron inertia.

We have made preliminary observations of the spatial localization of an electron plasma wave in a fluctuating plasma. The effect is related to the general wave phenomenon known as Anderson localization which is applicable both quantum mechanically and classically. Our experiment consists of a multipole discharge plasma in which a launched ion-acoustic mode provides a density fluctuation. We have observed an increase in the damping of an additional launched electron plasma wave which follows the predictions of a Mathieu-type equation for the wave amplitude evolution.

We report on a molecular-dynamics study of the wetting state of a system of hard spheres near a planar hard wall. A direct simulation at the melting point of a two-phase system between two walls develops all the way from complete wetting by fluid via a partial wetting state to a final arrangement of complete wetting by crystal. This implies that a hard-sphere fluid closely approaching coexistence from below should spontaneously crystallize at a smooth hard wall, contrary to existing beliefs.

A novel macroscopic stripe texture has been observed in freely suspended films of nonchiral liquid crystal, uniform stripes of alternating molecular orientation form spontaneously at the smectic-C–to–surface-hexatic phase transition and broaden with decreasing temperature. The stripes are identified as splay domains whose formation is attributed to the polar symmetry of the hexatic surface layers. Transverse (director bend) walls, which lead to an additional modulation of the basic one-dimensional pattern, are manifested inside thick circular islands as twelve-armed star defects.

We have studied by NMR the electronic properties of the stable quasicrystalline phases ${\mathrm{Al}}_{57}$${\mathrm{Cu}}_{10.8}$${\mathrm{Li}}_{32.2}$ and ${\mathrm{Al}}_{62}$${\mathrm{Cu}}_{25.5}$${\mathrm{Fe}}_{12.5}$ and of two crystalline approximants, the bcc R phase ${\mathrm{Al}}_{56}$${\mathrm{Cu}}_{12}$${\mathrm{Li}}_{32}$ and the rhombohedral ${\mathrm{Al}}_{62.8}$${\mathrm{Cu}}_{26}$${\mathrm{Fe}}_{11.2}$ phase. Low values of the density of states at the Fermi level are observed in the crystalline as well as in the quasicrystalline phases. The existence of a pseudogap at the Fermi level is therefore not a consequence of the quasiperiodicity. These results renew the debate on the stability of quasicrystals.

High-resolution heat-capacity experiments on free-standing films of the liquid-crystal compound 3(10)OBC near the smectic-A–hexatic-B phase transition have been conducted. The hexatic-B phase has been found to propagate into the smectic-A phase through a series of layer transitions, each appearing to be continuous. Furthermore, the evolution of the layer-by-layer transitions is shown to be inconsistent with recent theory regarding the fluctuation-induced forces of the highly anisotropic smectic phases.

Using an ac calorimetry technique we measured the specific heat at the nematic-isotropic, smectic-A–nematic, and smectic-A–isotropic phase transitions, for the alkylcyanobiphenyl liquid crystal nCB series confined to the 0.2-μm-diam pores of Anopore membranes. Studies were also performed as a function of nematic director alignment within the pores. Novel effects regarding specific-heat amplitudes, transition-temperature shifts, and broadening and rounding of phase transitions are found. They are strongly dependent on the director orientation and on the order of the phase transition.

We study properties of superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ on the basis of a new density matrix which is based on a shadow wave function of the roton. We have computed the energy, the Bose-Einstein condensate ${\mathit{n}}_0$(T), the correlations g(r;T) and S(k;T), and the strength Z(k;T) of the single-excitation peak of the dynamical structure factor. The temperature dependence of g(r;T) and S(k;t) is similar to that observed experimentally but we find that the relation of Hyland, Rowlands, and Cummings between g(r;T) and ${\mathit{n}}_0$(T) is not satisfied. A roton lowers the potential energy and the condensate is depleted by one atom every five to ten excited rotons.