A general formulation of linear and circular dichroism in the absorption of x rays in magnetically ordered systems is presented. The processes which induce sensitivity to magnetic properties are discussed. We demonstrate that the usually neglected electric quadrupole transitions can be as important as the dipole terms for the interpretation of magnetic dichroism experiments on transition metals and rare earths.

Ion photodesorption from rare-gas solids (Ar, Kr, Xe) is observed in the 25–120-eV photon energy range. Three different primary electronic processes, (i) formation of satellite states of the singly charged ions, (ii) direct double photoionization, and (iii) resonant double photoionization, are shown to produce ion desorption. A mechanism based on an interatomic charge exchange or ionization leading to a Coulomb repulsion between positive charges is proposed to account for ion desorption.

We report the first direct measurement of the effective magnetic penetration depth in oriented single crystals of κ-[BEDT-TTF${]}_2$Cu[NCS${]}_2$, with ${\mathit{T}}_{\mathit{c}}$(5 G)≊9 K. Results yield an effective in-plane value of ${\lambda }_{\mathit{e}\mathit{f}\mathit{f}}^{\mathit{b}\mathit{c}}$(0)≊9800 Å (for ${\mathit{H}}_{\mathrm{ext}}$≊3 kG), and a temperature dependence consistent with conventional s-wave pairing. Comparison with the London penetration depth, ${\lambda }_{\mathit{L}}$(0) (estimated to be ≊5100 Å), indicates a tendency toward dirty-limit superconductivity, with the ratio of coherence length over mean free path of ${\xi }_0^{\mathit{b}\mathit{c}}$/${\mathit{l}}_{\mathit{b}\mathit{c}}$≊2.7. From our results, it appears unnecessary to invoke any unconventional pairing schemes to explain the superconductivity in this material.

A new class of variational wave functions is proposed for the fractional quantum Hall effect in the presence of disorder at arbitrary electron densities. A consequence of these wave functions is a law of corresponding states which relates the behavior of the system in the fractional Hall regime to that in the integer Hall regime. For example, it is shown that the transition from the 1/3 to 2/5 plateau should be characterized by the same critical exponents as the transition between integer plateaus, while the transition between the 1 and 4/3 plateaus may be first order, and thus have no critical behavior.

We have investigated vibrational excitation of physisorbed ${\mathrm{O}}_2$ by electron impact in the 4–14-eV range, where a single broad resonance is observed in gas-phase studies. We show that by orienting the molecule in two different alignments on the surface of graphite it is possible to selectively populate two different negative-ion resonance states in this energy range, the ${}_{}{}^4{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{}{}_{}{}^{}$ state (at ∼8.5 eV) and the ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathit{u}}^{}{}_{}{}^{}$ state (at ∼6 eV), each of which leads to molecular vibrational excitation. Calculations show that this selective resonance population arises from the distinctive differential electron-capture cross sections of the two molecular states, into which electrons are ‘‘fed’’ by the surrounding surface structure.

We study numerically the dynamical equilibrium behavior for the uniformly driven, elastic model of Fukuyama, Lee, and Rice for pinned charge-density waves, in the critical region close to the threshold field for sliding, in two and three dimensions. We obtain a critical exponent for the mean velocity in good agreement with recent experiments, and scaling for the velocity correlation function, from which we extract a diverging correlation length. The correlation-length exponent ν is found to be less than 2/d (d is dimension), suggesting unusual critical behavior for this model.

Quadratic moments of a particle distribution being transported through a linear Hamiltonian system are considered. A complete set of kinematic invariants made out of these moments are constructed leading to the discovery of new invariants.

We examine the finite-size-scaling amplitudes of the free energy in incommensurate phases on a torus with periodic and twisted boundary conditions. We show that these amplitudes are equivalent to those of the six-vertex model with electric and magnetic defect lines. The twist angle generates magnetic defect lines, while the electric defect lines are generated by competition between the domain-wall separation and the finite system size. We calculate the amplitudes exactly for the free-fermion model and the spin-(1/2 XXZ chain, and conjectire the form of these amplitudes for a more general model. Numerical calculations employing the Bethe ansatz confirm our conjecture.

The likelihood that double inflation might break scale invariance and help produce cosmological large-scale structure is examined. The cumulative effects of quantum fluctuations in an auxilliary field χ, during the evolution of the first inflaton φ, can lead to a large dispersion in the probability distribution of χ when the auxilliary field becomes responsible for inflation. Hence, it may be very improbable that double inflation, and similar mechanisms that require tuning of scalar fields, produce breaks on scales of astrophysical interest.

We consider a boson field with a phase transition driven by a cosmologically small quartic self-coupling. While its short-wavelength components are stabilized, its very-long-wavelength components start a ‘‘slow-rolling’’ phase transition as soon as they come within their horizon. The Universe becomes filled with a critical density of ‘‘soft-boson’’ particles with a Compton wavelength of tens of kiloparsecs. Large-scale structure with present size tens of megaparsecs is inescapably formed by the wave-packet dynamics of such soft bosons. Baryons are gravitationally coupled to this structure. The Heisenberg uncertainty principle prevents soft bosons from falling into clusters of galaxies.

We calculate the rate of decay of a heavy neutrino into a lighter neutrino and a photon in a background that contain electrons but no μ’s or τ’s. Unlike the same decay in the vacuum, the rate of this process is not suppressed by the Glashow-Iliopoulos-Maiani mechanism. Some physical implications of the process are discussed.

We search for events in the Mark II detector at SLAC Linear Collider with the topology of a Z boson decaying into a pair of long-lived massive particles. No events that are consistent with the search hypothesis are found. Interpreting the long-lived particle as a sequential Dirac neutrino ${\nu }_4$ of the fourth generation, we exclude at the 95% confidence level a significant range of mixing-matrix elements of ${\nu }_4$ to other-generation neutrinos for a ${\nu }_4$ mass from 10 to 43 GeV/${\mathit{c}}^2$.

We report a measurement of the lifetime of the ${\mathit{B}}^0$ meson based upon 29-GeV ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ annihilation data taken with the Mark II detector at the SLAC storage ring PEP. The ${\mathit{B}}^0$ mesons are tagged by their decays into ${\mathit{D}}^{\mathrm{*}\mathrm{-}}$${\mathit{e}}^{+}$ν and ${\mathit{D}}^{\mathrm{*}\mathrm{-}}$${\mathrm{\mu }}^{+}$ν, where the ${\mathit{D}}^{\mathrm{*}\mathrm{-}}$ is tagged by its decay into ${\mathrm{\pi }}^{\mathrm{-}}$D¯ ${}_{}{}^0{}_{}{}^{}$. We reconstruct the decay vertices of 15 ${\mathit{B}}^0$-meson candidates and measure the ${\mathit{B}}^0$ lifetime to be 1.${20}_{\mathrm{-}\mathrm{0.360.14}}^{+0.52+0.16\mathrm{}}$ psec.

The dissociation of neutron-rich nuclei from secondary beams incident on several targets can be explained within two distinct models: (a) The weakly bound neutrons form clusters near the nuclear surface, and (b) all protons can vibrate against all neutrons in a soft mode. We show that the momentum widths of the projectile fragments, as well as the total cross sections for the dissociation, are consistent with both hypotheses. Consequently, the interpretation of almost all recent experimental studies with secondary radioactive beams is ambiguous.

It is shown that angular distributions of Auger electrons and x rays from deexcitation of doubly excited states produced in the resonant transfer and excitation of projectiles in collisions with light targets are, in general, not isotropic. The detailed theoretical results for the 2${\mathit{p}}^2$ ${}_{}{}^1{}_{}{}^{}\mathrm{D}$ resonance in ${\mathrm{F}}^{8+}$+e/r${\mathit{H}}_2$ are presented at a projectile energy of 20 MeV.

We show that by applying a strong-coupling field between a metastable state and the upper state of an allowed transition to ground one may obtain a resonantly enhanced third-order susceptibility while at the same time inducing transparency of the media. An improvement in conversion efficiency and parametric gain, as compared to weak-coupling field behavior, of many orders of magnitude is predicted.

On the route to turbulence in electrohydrodynamic convection of nematic liquid crystals, the last bifurcation is spatially inhomogeneous via nucleation. Such a transition occurs between two different turbulent states (DSM1 and DSM2). We find good agreement between the nucleation rate of DSM2 nuclei and an expression from conventional nucleation theory. The motion of the DSM1-DSM2 interface behaves similar to propagating fronts in other nonequilibrium systems. Disclinations in the director field are created during the transition, similar to the vortex filaments in the TI-TII transition in superfluid He II.

The stability of Taylor-Couette flow subject to an external Coriolis force is studeid experimentally. The external Coriolis force stabilizes the flow. At larger dimensionless rotation rates stabilization is dramatic, reaching a value greater than 300%. The stability behavior of this system exhibits striking qualitative and quantitative similarity to the behavior of Bénard convection subject to rotation, and qualitative similarity to Bénard convection and Taylor-Couette flow subject to a magnetic field.

We have measured the time dependence of interface formation between two polymers, below their critical temperature for phase separation, using the ${}_{}{}^2{}_{}{}^{}\mathrm{H}$${(}^3$He${,}^4$He${)}^1$H nuclear reaction as a direct profiling technique. We find that the width of the interface initially increases with time as ${\mathit{t}}^{\mathrm{\alpha }}$, where the exponent α=0.34±0.06 is significantly lower than its value of 0.5 for free diffusion.

Quasielastic-light scattering above the nematic–smectic-C transition near the nematic–smectic-A–smectic-C multicritical point shows that the behavior of the splay-mode correlation time is consistent with that of the viscosities. The anomalous bend-mode scattering is found to exhibit two correlation times close to the transition. The relative amplitude of the fast fluctuatiosn has a temperature dependence similar to that of the longitudinal smectic correlation length, suggesting that the additional light scattering is due to tilt fluctuations that manifest themselves in the nonhydrodynamic regime.