We find that for Peccei-Quinn symmetry-breaking scales ≲4×${10}^8$ GeV (corresponding to axion masses ≳0.03 eV) thermal production of axions in the early Universe (via the Primakoff and photoproduction processes) dominates coherent production by a factor of about $1200{\left[\frac{m_a}{\left(1\mathrm{} \mathrm{eV}\right)}\right]}^{2.175}$. The photon luminosity from the decays of these relic axions leads to an upper limit to the axion mass of order 2-5 eV. If the axion mass saturates this bound, relic axion decays may well be detectable.

We use a variational approach to study Abelian vortices, both the ordinary and bosonic superconducting varieties. We present accurate results for the energy per length. For superconducting strings we map out the parameter space of solutions, quantify the critical current, discuss the quench transition, and investigate the possibility of static solutions where electromagnetic stresses balance the string tension.

A linearization scheme is proposed for the general Hamiltonian of an interacting fermion system, consisting of a mean-field approximation in which pairing and umklapp play dominant roles. A variety of models emerge, characterized by a hierarchy of spectrum-generating algebras and superalgebras, of which some are supersymmetric. The superconducting phase transition is shown to be related to supersymmetry breaking.

We measure the response of the quark number to an infinitesimal chemical potential in high-temperature QCD with two light flavors of dynamical fermions. In the chirally symmetric phase the susceptibilities for quark number density and for the density of the third component of isospin are large and equal within statistics, which is consistent with a plasma of light quarks. In the broken-symmetry phase the susceptibility for quark number density is small, as expected from quark confinement.

If the Higgs-boson mass ${\mathrm{m}}_{\mathrm{H}}$ is larger than 1 TeV, because of its large width it is almost impossible to detect its presence at the superconducting super collider. It is, however, easier to detect a corresponding vector meson V which is shown to satisfy a mass relation ${\mathrm{m}}_{\mathrm{V}}$=${\mathrm{m}}_{\mathrm{H}}$/ √2 on the assumption of the validity of the Kawarabayashi-Suzuki-Riazuddin-Fayyazuddin relation. This detection would determine the remaining parameter ${\mathrm{m}}_{\mathrm{H}}$ of the minimal standard model with a strongly coupled Higgs sector.

In a phase-shift analysis of all Pp scattering data below $T_{\mathrm{lab}=350\mathrm{}}$ MeV, where ${\chi }^2$/$N_{\mathrm{DF}=1.07\mathrm{}}$ ($N_{\mathrm{DF}}$ is number of degrees of freedom) is reached, the long- and intermediate-range pp interaction has been studied. Using as intermediate-range interaction the Nijmegen potential, we find for the pp${\pi }^0$ coupling constant ${\mathit{f}}_0^2$=(72.5±0.6)×${10}^{\mathrm{-}3}$ or ${\mathit{g}}_0^2$=13.1±0.1 and for the ${\pi }^0$ mass 134.7±2.1 MeV. Even when we take account of the model dependence due to the potential tail, this value of $f_0^2$ is significantly lower than the value of the charged coupling constant in πN scattering, indicating a large breaking of charge independence.

A longitudinal/transverse separation of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(e,e’p) reaction in the quasielastic region has been performed in parallel kinematics. Above the two-particle emission threshold a broad bump is seen which has been attributed to knockout from the deeply bound s shell. The s-shell region shows a large transverse enhancement compared to distorted-wave impulse-approximation calculations based on free-proton form factors. This enhancement increases with missing energy, indicating that a nonquasielastic reaction mechanism plays a significant role. The p shell is consistent with the free-proton behavior.

Multiconfiguration Hartree-Fock theory and density-functional theory both show that the negative ions ${\mathrm{Ca}}^{\mathrm{-}}$ and ${\mathrm{Sc}}^{\mathrm{-}}$ have stable ground states, the extra electron being a 4p electron. The multiconfiguration Hartree-Fock method, with a relativistic shift correction, predicts an electron affinity of 0.045 eV for Ca, a result in excellent agreement with recent experiment. A less accurate calculation for Sc yields an electron affinity of 0.152 eV. Density-functional theory gives a simple explanation of why the extra electron goes into the 4p orbital rather than a 3d orbital.

We present experimental evidence for the existence of a stable ${\mathrm{Ca}}^{\mathrm{-}}$ ion formed in the bound (4${\mathrm{s}}^2$4p${)\mathrm{}}^2$P state. This result represents the first report of a stable negative ion for a group-IIA element. The structure of ${\mathrm{Ca}}^{\mathrm{-}}$ was determined by means of photoelectron detachment spectroscopy. The electron affinity of Ca was measured to be 0.43±0.007 eV, which is in good agreement with a recent calculation.

We present experimental results showing that channeling measurements with fast stripped heavy ions incident on thin crystals can allow a detailed study of radiative electron capture. Charge-state measurements and photon-energy spectra have been used to deduce cross sections of radiative capture into the K, L, and M shells of 25-MeV/u ${\mathrm{Xe}}^{53+}$ ions. The orientation dependence of the positions and shapes of associated photon lines has been observed.

A search for permanent electric dipole moment of ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ atoms has yielded the null result d${(}^{199}$Hg)=(0.7±1.5)×${10}^{\mathrm{-}26}$ e⋅cm, which improves by an order of magnitude the limits on several possible interactions that violate time-reversal symmetry. The experiment was performed by the use of optically pumped atomic oscillators to measure any shift in the NMR frequency of ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ (I=(1/2) produced by an external electric field.

We report the first study of the energy spectra of electrons from autoionizing quasimolecules formed at very low collision energies (E${\mathrm{¯}}_{\mathrm{rel}=1.6\mathrm{}}$ meV). The electron spectra due to ionizing He($2^3$S)-He($2^3$S) and He($2^1$S)-He($2^3$S) collisions in a single atomic beam show significant structure, which is explained on the basis of accurate new ab initio potentials for the relevant excited states. Fast oscillations due to the interference of incoming and outgoing waves of the heavy-particle motion are observed in both the experimental He($2^3$S)-He($2^3$S) spectrum and the corresponding quantum mechanical calculations.

We present absolutely timed spectral measurements, as well as other data, on the exploding-foil Ne-like Se soft–x-ray laser scheme. The data show that amplification occurs near the peak of the optical heating pulse, in agreement with our original theoretical predictions. A recently published alternative scenario predicted that gain develops only after the heating pulse, via recombination in an overionized, rapidly cooling plasma. Since our new data differ so sharply from that prediction, we reexamine the theoretical basis for that alternative scenario.

Results of first-principles calculations for a large number of geometries for a single, polymeric hydrogen fluoride chain are presented. For the F-F-F bond angle kept fixed at 180° two minima show up, whereas for 120° only one minimum is found. A global minimum with bond lengths and angles close to the experimental values is found. The results are compared with those on a single HF monomer.

A shift in a continuum threshold due to the presence of a strong laser field has been directly observed. An increase in the photodetachment threshold of ${\mathrm{Cl}}^{\mathrm{-}}$ was observed in the presence of 1064-nm-wavelength radiation.

A new model of relativistic Applied-B ion diodes is presented that appears to explain a previously discovered empirical scaling law. The model is based on a self-consistent calculation of the diamagnetic effect of virtual-cathode location coupled with the assumption of a uniform electron-density profile in the sheath. The success of this model greatly increases our understanding of the undesirable phenomenon of impedance collapse in applied-B diodes and suggests a simple measure for improving their performance.

We observe linear and nonlinear features of a strong plasma/magnetic field interchange Rayleigh-Taylor instability in the limit of large ion Larmor radius. The instability undergoes rapid linear growth culminating in free-streaming flute tips.

In the Joint European Torus the ablation of injected pellets produces a striking resonance effect when the pellets reach surfaces with q values 1 and (3/2. Subsequently, structures with mode numbers m=1,n=1 and m=3,n=2 are observed with the soft-x-ray cameras for up to 2 s as compact snakelike perturbations. These structures, which persist through several sawtooth collapses, give information on the radii of the q=1 and q=(3/2 surfaces and the q-profile evolution. The observations can be explained by the formation of magnetic islands.

We report a medium-energy ion-scattering study of the (1×2) reconstruction of the Ag(110) surface induced by submonolayer amounts of K. A qualitative comparison between ion-scattering data from the clean and K-covered surfaces shows that the (1×2) periodicity is caused by a missing-row reconstruction of the Ag substrate. Computer simulations support this conclusion and provide detailed information on the atomic positions. Our observations support a recent model by Heine and Marks explaining surface relaxation and reconstruction in terms of the occupation of s-p and d electronic levels.

We have fabricated wire networks in the form of triangular arrays of third-order Sierpinski gaskets and percolation arrays on square lattices. For the gaskets the superconducting phase boundary, ${\mathrm{T}}_{\mathrm{c}}$(H), exhibits a clear crossover between the homogeneous and inhomogeneous (fractal) regimes. This is formally equivalent to the phonon-fracton crossover. Surprisingly, the random, square-lattice percolation networks, which are expected to exhibit a similar crossover, seem to behave in a manner characteristic of two-dimensional systems, independent of length scale.