We have measured the ac nonlinear susceptibilities ${\mathrm{\chi }}_3^{\mathcal{’}}$, ${\mathrm{\chi }}_5^{\mathcal{’}}$, and ${\mathrm{\chi }}_7^{\mathcal{’}}$ of very dilute Ag:Mn spin-glasses above and below the transition temperature ${\mathrm{T}}_{\mathrm{g}}$ as functions of frequency, temperature, and magnetic field. In the static limit, these quantities display well defined critical singularities at ${\mathrm{T}}_{\mathrm{g}}$. The nonlinear susceptibilities can be fitted above ${\mathrm{T}}_{\mathrm{g}}$ by powers of frequency with weakly temperature-dependent exponents. While the effective exponents satisfy the relations imposed by static and dynamic scaling, the observed temperature and frequency roundings suggest the presence of additional length scales.

The energetics of reconstruction models of the ideal W(001) and Ta(001) surfaces are studied by the general-potential linearized augmented plane-wave method. The ideal W(001) surface is found to be very unstable to the low-temperature Debe and King c(2×2) structure, gaining an energy of about 1200 K upon reconstruction. It is thus not likely that the high- (room-) temperature phase is in the ideal p(1×1) structure. It is determined that the instability is due to local bonding effects and not to a Fermi-surface instability.

The nuclear magnetic resonance frequencies of ${}_{}{}^{201}{}_{}{}^{}\mathrm{Hg}$ (I=(3/2)) and ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ (I=(1/2)) have been compared by use of optically pumped atomic light absorption oscillators to see if the relative frequencies depend on the orientation of the quantization axis in space. The null result δ${\nu }_2$<5×${10}^{\mathrm{-}7}$ Hz improves by over 3 orders of magnitude recent limits on any quadrupolar interactions violating spatial isotropy, and can be interpreted as the most precise test yet of local Lorentz invariance. The experiment also improves the limits on anisotropic dipole interactions.

The beautiful scheme of Bars and Visser by which feeble intermediate-range forces arise from higher dimensions is investigated. It is found that the desirable relation between the coupling and mass of the feeble-force vector, $m_V$≊$g_V$${\Lambda }_{\mathrm{weak}}$, is difficult to achieve in simple schemes of symmetry breaking, though it is possible if new scales are introduced. An analogy is made with the paraphoton picture of Holdom.

Through use of a previous calculation of the light-by-light scattering contribution to the electron anomaly in sixth order, it is shown that theory and experiment disagree by 4 standard deviations. Our result is [a≡(g-2)/2] $a_e$(theor)-$a_e$(expt)=604(149) ×${10}^{\mathrm{-}12}$. .AE

A new resolution to the U(1) problem is proposed without direct reference to spontaneous chiral-symmetry breaking. The parity and flavor symmetry which correspond to the neutral-pion operator are spontaneously broken when we change the mass parameter M. Therefore the neutral pion becomes massless at the phase-transition point where the correlation length diverges, while the η meson remains massive. Furthermore, the charged pion becomes the Nambu-Goldstone boson in the parity- and flavor-symmetry-breaking phase.

We report measurements of two-particle correlations in rapidity space between a p¯ or Λ¯ and an additional p, p¯, Λ, or Λ¯. We find evidence for local conservation of baryon number, and for the first time observe a pronounced anticorrelation between baryons with the same value of baryon number. Such an anticorrelation is expected in fragmentation models where the rapidity order of particles closely reflects their ‘‘color order,’’ as is the case, for example, in recent versions of the Lund string model.

An absolute measurement of ${\pi }^0$ photoproduction on the proton has been carried out in the threshold region (from 144.7 to 173 MeV) by use of tagged annihilation photons. The measured cross sections, differential in the recoiling-proton energy, are used to perform a multipole analysis which gives a value & &, in disagreement with low-energy-theorem predictions. Total cross sections and coefficients of the ${\pi }^0$ angular distribution are presented.

The nuclear matrix element for 2ν double-beta decay is calculated within the quasiparticle random-phase approximation. It is shown that the decay matrix element passes through zero as a function of the strength $g^{\mathrm{pp}}$ of the particle-particle component of the spin-isospin polarization force, neglected previously. The analysis of electron capture/${\beta }^{+}$ decay rates for semimagic neutron-deficient nuclei suggests values for $g^{\mathrm{pp}}$ in the very vicinity of this zero, which gives rise to long lifetimes. The qualitative features of nuclear ββ decay are illustrated with the example of an exactly soluble model.

The pion spectra observed in the inclusive double-charge-exchange reactions ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(${\pi }^{+}$,${\pi }^{\mathrm{-}}$)4p and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(${\pi }^{\mathrm{-}}$,${\pi }^{+}$)4n are strikingly different from those in heavier nuclei, exhibiting a prominent peak at high outgoing pion energies. The shapes of these spectra, while qualitatively consistent with two sequential single-charge-exchange processes, are not yet quantitatively understood.

We report the observation of intensity-dependent angular distributions of photoelectrons in multiphoton ionization of xenon by 1064-nm light in the intensity range of (0.5–5)×${10}^{13}$ W/${\mathrm{cm}}^2$. The intensity dependence is shown to arise from the scattering of the photoelectrons from the ponderomotive potential created by the intense optical fields. This phenomenon is a general, final-state effect which can severely restrict the usefulness of angular distribution measurements in high-intensity multiphoton ionization.

It is shown both experimentally and theoretically that a Rydberg circular atom keeps its maximum momentum only if it is submitted to a nonzero static electric field whose direction is constant or slowly varying. The minimum characteristic time of the field-allowed rotation is determined. The implications of this effect for a future high-resolution microwave spectroscopy experiment on circular Rydberg atoms is discussed.

An oscillatory exchange of atoms governed by the phases of the ‘‘macroscopic wave functions’’ between two traps containing Bose condensates, as might be realized with laser cooling and trapping is predicted. The discussion exploits analogs from lasers and the Josephson junction.

We discuss the onset of convection in viscoelastic liquids. We find for the first time that for some value of the parameters the tricritical point of one of the instability branches coincides with the codimension two point. Such a phenomenon seems to have no analog in systems close to thermodynamic equilibrium. In addition we predict that the oscillatory instability sets in as finite-amplitude traveling waves for most Prandtl numbers.

Considerable progress has been made in the experimental observation of Anderson localization and quantum eigenstate coherence for electrons in disordered solids. The coherence effects deduced from conductivity measurements require some corrections for inelastic scattering, and often the necessary information is imprecisely known. In this letter we report detailed observations of inelastic effects in an acoustic localization experiment where parameters may be precisely controlled and measured; some phase correlation effects are evident.

A systematic study of the near-edge x-ray-absorption fine structure for single-layer coverage of ${\mathrm{C}}_2$${\mathrm{H}}_2$, ${\mathrm{C}}_2$${\mathrm{H}}_4$, and, for the first time, ${\mathrm{C}}_2$${\mathrm{H}}_6$ chemisorbed on Cu(100) and Ag(100) allows the determination of the molecular orientation and bonding strength. The first surface extended x-ray-absorption fine structure at the carbon K edge yields the nearest-neighbor distance to be 1.9(1) Å for ${\mathrm{C}}_2$${\mathrm{H}}_2$ and ${\mathrm{C}}_2$${\mathrm{H}}_4$ on Cu. A comparison of the σ shape-resonance position in the gas phase, chemisorbed on Ag, Cu, and Pt, is presented.

Using conformal-invariance arguments in two dimensions, we identify the exact infinite series of basic surface conformal dimensions for polymers, checked by transfer-matrix calculations for the n=0 vector model on a strip. For a self-avoiding branched polymer of arbitrary and fixed topology, near a surface or a wedge, we give the exponent γ in two dimensions as a function of the topology and of the wedge opening angle.

By use of a free-energy model, the properties of a fluid composed of neutral atoms and diatomic molecules, positive ions and molecular ions, and an electron Fermi gas are calculated. The interactions include excluded volume, internal molecular binding, electron-neutral s-wave scattering, and screened Hartree interactions. For rubidium and cesium parametrizations, the vapor-liquid phase transitions with their critical points, the insulator-metal transitions, and the isothermal electrical conductivities and magnetic susceptibilities are obtained.

The assumption that minute defects and impurities may be the cause for discrepancies between experiment and theory on physisorbed films is confirmed for the first time in direct experiments. A change of 30° in the orientation of a Kr layer on Pt(111) induced by H and CO precoverages as low as 0.1%, via the blocking of step sites, is demonstrated by high-resolution He diffraction.

Using a nonlinear response theory that accounts for correlation in the liquid, we have determined the modulation potential for a 2D Rb liquid in graphite from a measurement of the Rb contribution to the graphite Bragg peaks. The resulting potential is almost perfectly represented by a set of six simple sine waves; its value at a hexagon center is ${\mathrm{V}}_0$=-0.0735 eV. At a bond midpoint the potential is ${\mathrm{V}}_{\mathrm{b}}$=+0.0185 eV. This result is checked with numerical simulations, and the implications for other 2D systems, including rare gases on graphite, are discussed.