Tunneling spectroscopy performed with the scanning tunneling microscope is used to study image-type surface states. The tunneling tip causes a Stark shift and expansion of the hydrogenic image-state spectrum, permitting a clear resolution of the individual states. A simple theoretical model provides a quantitative connection between the tunneling data and both previous and new inverse-photoemission data.

A variational wave function for the Kondo-lattice limit of the periodic Anderson model is evaluated with a Gutzwiller approximation. We obtain a characteristic energy from this coherent wave function of the Kondo form but with a different exponent in the case of finite degeneracy. The effective mass and charge and spin susceptibilities are evaluated, and only in the case of large degeneracy and not too small hybridization strength is a heavy-Fermi-liquid state stable against magnetic order.

I show that recently reported oscillations in the current-voltage characteristics of GaAs-AlGaAs tunnel junctions are due to a combination of self-energy corrections to the density of states from electron-phonon interactions and successive phonon emission in the GaAs buffer layer. Alternative models based on space-charge modulation or point-contact transport do not explain the experimental data.

The structure of constrained Hamiltonian systems is investigated. The structure functions are shown to obey remarkable identities which ensure the existence of the Becchi-Rouet-Stora symmetry for any gauge theory.

We point out that for $W$-pair production from $e^{+}{e}^{-}$ or $q\overline{q}$ beams, the correlation between the decay planes of the $W\text{'}\mathrm{s}$ is numerically negligible (at tree level) in the standard model. This occurs for the production of $\mathrm{WW}$ via intermediate fermions or gauge bosons and independently for $\mathrm{WW}$ produced via Higgs-boson exchange, and is not restricted to two-body diagrams. In general, the correlation need not vanish, and so a nonzero correlation would be a clear signal of physics beyond the standard model. Definition of the $W$-decay plane should be fairly straightforward from the decay $W\to f\overline{f}$ and, hence, the correlation measurement is experimentally feasible.

A new gauge-invariant order parameter is introduced for the Abelian Higgs model and used to prove the existence of a phase transition for the lattice theory in three or more dimensions. In Landau gauge this order parameter is the limit of $〈\phi \mathrm{}\left(x\right)\mathrm{}\overline{\phi }\mathrm{}\left(y\right)\mathrm{}〉$ as $\mathrm{}|x-y|\mathrm{}\to \infty$.

We have performed a high-statistics experiment on the reaction ${\pi }^{-}p\to K^{+}{\overline{K}}^0{\pi }^{-}n$ at 8.0 GeV/c. A Dalitz-plot analysis of the $K^{+}{\overline{K}}^0{\pi }^{-}$ system finds that the $D\left(1285\right)\mathrm{}$ is a $J^{\mathrm{PG}}=1^{++}$ state coupling predominantly to a $\delta \pi$ decay channel, while the $E\left(1420\right)\mathrm{}$ peak consists mostly of a $J^{\mathrm{PG}}=0^{-+}$ wave with a substantial $\delta \pi$ decay mode. There is little evidence of a $1^{++}$ resonance at the $E$ mass.

We show that a quaternionic quantum field theory can be formulated when the numbers of bosonic and fermionic degrees of freedom are equal and the fermions, as well as the bosons, obey a second-order wave equation. The theory is initially defined in terms of a quaternion-imaginary Lagrangean using the Feynman sum over histories. A Schrödinger equation can be derived from the functional integral, which identifies the quaternion-imaginary quantum Hamiltonian. Conversely, the transformation theory based on this Hamiltonian can be used to rederive the functional-integral formulation.

The relation $\frac{m_t}{m_c}\approx \frac{m_b}{m_s}$, which predicts a top-quark mass close to 40 GeV, is derived in the context of SO(10) (and ${\mathrm{E}}_6$) grand-unified theories with suitable intermediate scales.

The circular polarization of the $\gamma$ rays emitted in the transition from the 1.081-MeV state to the ground state in ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$ has been measured to be (1.6±5.6)×${10}^{-4\mathrm{}}$, corresponding to a parity-nonconserving (PNC) matrix element $|〈0^{+}, I=1|V^{\mathrm{PNC}}|0^{-}, I=0\mathrm{}〉|=0.03\mathrm{}\pm 0.10$ eV. The weak pion-nucleon coupling constant deduced from the weighted average of all recent ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$ measurements is (${0.28}_{-0.28\mathrm{}}^{+0.89\mathrm{}}$)×${10}^{-7\mathrm{}}$. This result, together with PNC matrix elements in other experiments, suggests that the isovector weak $\mathrm{NN}$ interaction may be strongly suppressed compared with the isoscalar weak $\mathrm{NN}$ interaction.

A new measurement of the circular polarization $P_{\gamma }$ of the 1081-keV $\gamma$ line in ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$ has been performed. The result is $P_{\gamma }\left(1081\mathrm{} \mathrm{keV}\right)=(2.7\mathrm{}\pm 5.7)\times {10}^{-4\mathrm{}}$. This result, when averaged with those of recent measurements in ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$, sets an upper constraint for the absolute value of the coupling constant $f_{\pi }$ of the weak $\pi \mathrm{NN}$ interaction of $\left|f_{\pi }\right|<~1.5\times {10}^{-7\mathrm{}}$.

We present results of an experimental study of the shape of the energy spectrum for the decay ${}_{}{}^{35}{}_{}{}^{}\mathrm{S}\to {}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}+e^{-}+{\nu }_e$. The measurements were performed to search for evidence of a beta-decay branch with a heavy neutrino. No evidence for heavy neutrinos is observed. In particular, our limit for the branch to a 17-keV neutrino is 0.4%, in serious disagreement with the 3% branch claimed by Simpson.

We have measured fission and particle-evaporation cross sections for the nuclei ${}_{}{}^{170-188}{}_{}{}^{}\mathrm{Pt}$ formed with the reactions ${}_{}{}^{58,64}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{112-124}{}_{}{}^{}\mathrm{Sn}$. This represents the first systematic study of the decay of compound nuclei formed with heavy projectiles ($A_{\mathrm{proj}}\gtrsim \frac{1}{2}{A}_{\mathrm{target}}$), and thus endowed with large angular momenta at relatively low excitation energies. Using a statistical model and a single set of input parameters, we have reproduced all the data.

Conventional treatments of atomic effects in beta decay may fail for electron momenta comparable in magnitude to the inverse of the Bohr radius. Exchange corrections are shown to produce a distortion of the tritium beta spectrum similar in shape to that for heavy-neutrino emission, though significantly smaller. The limitations of standard screening corrections are discussed.

Gamma-ray spectra of neutron-deficient isotopes between cerium ($Z=58\mathrm{}$) and gadolinium ($Z=64\mathrm{}$) have been investigated. New bands of states were identified in many even-even, odd-$A$, and odd-odd nuclei. This Letter reports results on the ground-state bands in the even-even nuclei ${}_{58}{}^{126}{}_{}{}^{}\mathrm{Ce}_{68}^{}{}_{}{}^{}$, ${}_{60}{}^{128,130,132}{}_{}{}^{}\mathrm{Nd}_{68,70,72}^{}{}_{}{}^{}$, ${}_{62}{}^{134,136}{}_{}{}^{}\mathrm{Sm}_{72,74}^{}{}_{}{}^{}$, and ${}_{64}{}^{138,140}{}_{}{}^{}\mathrm{Gd}_{74,76}^{}{}_{}{}^{}$. The systematic trends of deformation are presented and compared with theoretical predictions. The lightest isotopes appear to be axially symmetric rotors with ${\epsilon }_2\gtrsim 0.3$.

We report on the photodissociation of neutral diatomic molecules in a molecular-beam experiment where all the relevant quantities are well defined. The velocity and angular distributions and the internal states of the fragments were determined by Doppler spectroscopy. The quasibound level $v^{\prime }=31\mathrm{}$, $J^{\prime }=42\mathrm{}$ of the $B{}_{}{}^1{}_{}{}^{}\Pi _{\mathrm{u}}^{}{}_{}{}^{}$ state of ${\mathrm{Na}}_2$ dissociates into ${\mathrm{Na}}^{*}3{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ and $\mathrm{Na}3{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ atoms with an angular distribution characterized by $\beta =-1\mathrm{}$. Direct dissociation of the $B{}_{}{}^1{}_{}{}^{}\Pi _{\mathrm{u}}^{}{}_{}{}^{}$ state yields only ${\mathrm{Na}}^{*}3{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ fragments, which does not support reported ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ fragment emission. From two-photon dissociation we obtain ${\mathrm{Na}}^{*}3{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ fragments with much larger kinetic energy and a different angular distribution.

The first computer simulation of the time-correlation functions of the intermolecular Coriolis and centrifugal forces reveals that these functions are different in the laboratory frame for (R)- and (S)-CHBrC1F and the racemic mixture. This (observable) laboratory-frame difference is due to the differential statistical interdependence in this frame of a molecule's rotation on its own translation in enantiomers and mixture.

We present theory and experiments to show that the efficiency of four-wave mixing in photorefractive materials can be enhanced by use of optical waves of slightly different frequencies. The optimum frequency shift scales inversely with the response time of the material. We show that the ∼1-Hz frequency shift previously observed in the output of a self-pumped phase conjugator that used photorefractive BaTi${\mathrm{O}}_3$ is the result of this inherent property of four-wave mixing.

The convection of a magnetic field in an overdense plasma by the Nernst effect is studied with a kinetic description of electron transport. The magnetic field is found to be always strongly coupled to the heat flow, even when the latter is nonlinear (but classical), which places a constraint on flux-limitation schemes in magnetohydrodynamics calculations. The cross-field, Righi-Leduc heat flux is found to require a lower flux limiter than does the inward heat flux into the target.

It is shown experimentally that the lower-hybrid-current-drive density limit is a function of the rf source frequency. While in previous 800-MHz experiments this limit occurred at ${\overline{n}}_e=6\mathrm{}\times {10}^{12}$ ${\mathrm{cm}}^{-3\mathrm{}}$, with a newly installed 2.45-GHz, 100-kW rf system on the Versator II tokamak, fully rf-driven discharges have been achieved at densities up to ${\overline{n}}_e=1.0\mathrm{}\times {10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$, without increase of the toroidal magnetic field ($B<~13$ kG, $\frac{{\omega }_{\mathrm{pe}}^2}{{\omega }_{\mathrm{ce}}^2}>1\mathrm{}$). Incremental current increases in Ohmically heated discharges have been observed at densities exceeding ${\overline{n}}_e=2.0\mathrm{}\times {10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$.