For a $N$-component isovector field $\varphi$, ${\left({\varphi }^6\right)}_3$ is free in the infrared limit for all $N$. If $N$ is sufficiently large there is also an ultraviolet stable fixed point, calculable within perturbation theory, at which anomalous dimensions are $\sim N^{-1\mathrm{}}$.

A relativistic Faddeev calculation of the pion-deuteron breakup reactions in the region of the (3, 3) resonance has been performed, using as input all the $S$- and $P$-wave pion-nucleon and $S$-wave nucleon-nucleon channels, as well as treating relativistically both the spin and the space variables. Theoretical predictions for the energy dependence of the integrated breakup cross sections, and for the differential cross section of the kinematically complete experiment at 228 MeV, are compared with available data.

Energetic electron bunches in storage rings produce pulsed bursts of incoherent synchrotron radiation. It is pointed out that they should also produce a roughly comparable power output of coherent radio-frequency radiation. Thus electron storage rings might additionally serve as pulsar simulators, producing a similar spectrum of coherent emission, the properties and modification of which could be studied in the laboratory. A spontaneous bunching of electrons (artificially bunched here) might be evidenced as "superbunching."

Results are presented for the effect of the three-body force on the charge form factors of the $A=3\mathrm{}$ nuclei. Mesonic exchange currents, isobaric processes, and other effects of relativistic order are included in the present calculation. The evaluation of the form factors is extended to values of momentum transfer $q=10.0\mathrm{}$ ${\mathrm{fm}}^{-1\mathrm{}}$, and their model dependence is explored.

Experiment and theory have been used to determine the final-state symmetry for the $n=2\mathrm{}$ state in photoionized helium. The angular asymmetry parameter $\beta$ has been measured as a function of photon energy by means of angle-resolved photoelectron spectroscopy. From these measured $\beta$ values, which are a weighted average of ${\beta }_{2s}$ and ${\beta }_{2p}$, together with the theoretical values of ${\beta }_{2p}$ and ${\beta }_{2s}$, the ratio, $R$, of the partial $2p$ photoionization cross section to the partial $2s$ photoionization cross section has been obtained.

An experiment is described demonstrating that for fast-ion bombardment of thin foils, projectile Rydberg atoms and convoy electrons emerge with comparable probabilities. These Rydberg atoms can readily ionize in the fields of electron spectrometers employed for measurements on convoy electrons, producing beam-velocity electrons which contribute significantly to the "cusp electron" spectra observed. This Rydberg contribution to the shape and intensity of the cusp peak has not been taken into account in previous treatments.

A sodium atomic beam with density ${10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$ was illuminated by cw dye laser radiation (a few watts per square centimeter) tuned to the $D_2$ resonance line. In the energy spectrum of the emitted electrons, several lines were observed between 4 and 7 eV. Their positions and intensities indicate that seed electrons are produced either via associative ionization or via collisional ionization from excited states populated by energy-pooling collisions. These electrons are then heated through successive superelastic collisions with excited $3p$ atoms.

Experimental evidence is presented for the effect of photoionization of $n{s}^2$ atomic subshells with unpolarized radiation that leads to highly polarized photoelectrons in angular-resolved measurements. Like the Fano effect, the observed phenomenon is caused by spin-orbit interaction in the continuous spectrum. The spin polarization essentially depends on the phase-shift difference between the $\epsilon p_{\frac{1}{2}}$ and $\epsilon p_{\frac{3}{2}}$ continua.

An experiment has been performed with atomic hydrogen which yields an upper limit on an intrinsic violation of Laporte's rule. This limit, expressed in terms of mixing of the $2S_{\frac{1}{2}}-2\mathrm{}{P}_{\frac{1}{2}}$ parity doublet, is 1.5×${10}^{-8\mathrm{}}$.

The associative ionization ${\mathrm{Na}}^{*}+{\mathrm{Na}}^{*}\to {{\mathrm{Na}}_2}^{+}+e$, when Na atoms in a single thermal beam are excited by linearly polarized light, was observed. The ion yield increases by a factor of 1.7 when the light polarization vector is rotated from a perpendicular to a parallel direction with respect to the beam. A theoretical analysis shows that the ionization rates $K$ obey the relations $K(\frac{1}{2}, \frac{3}{2})=0\mathrm{}$ and $K(\frac{1}{2}, \frac{1}{2})=1.4K(\frac{3}{2}, \frac{3}{2})$, where the arguments indicate the initial magnetic substates $\left|M_J\right|$ of the two colliding atoms.

The dipole matrix element for the Cs $9d\to \epsilon f$ photoionizing transition is found theoretically to have three zeros, as a function of photoelectron energy. In addition, a zero in the $d\to p$ channel also appears. The explanation of the phenomenon in terms of relative phase shifts is given and the generality of these multiminima is discussed. The consequences of these zeros in cross sections and angular distributions are also spelled out.

It is shown that the transmitted light from a bistable optical cavity exhibits instability leading to periodic and chaotic self-pulsations, when the relaxation time of the medium is much longer than the delay time of the feedback of light. This instability, which is different from the delay-induced one predicted recently by the authors and observed by Gibbs and co-workers, is interpreted as a self-induced Rabi nutation of the electric field vector.

A simple model for ion radial transport in the resonant plateau regime is derived. It is shown that the ion diffusion coefficient is insensitive to the radial electric field over a wide range of parameters. With use of this result, and the expression for the electron flux, a self-consistent picture of ambipolar tandem operation for quadrupole symmetric systems is obtained and compared with experiment.

The observation of a plasma current generated by the absorption of rf waves at the electron cyclotron resonance is reported. The current flows in opposite directions on opposite sides of the electron-cyclotron-resonance position, confirming that the current is driven by asymmetric heating of the electron distribution function. The current (∼30 mA/W) varies linearly with microwave power and electron temperature and inversely with electron density.

A simple model of classical diffusion on a random chain is studied. The velocities to the right and to the left are calculated. When one changes continuously the probability distribution $\rho$ of the hopping rates, a whole region is found where these two velocities vanish. In this region, the distance $R$ covered by a particle during the time $t$ behaves like $R\sim t^x$, where $x$ depends continuously on $\rho$. The exponent $x$ is calculated for a simple example.

High-temperature series for two bcc lattice models which interpolate between the Gaussian (or free-field) model and the $S=\frac{1}{2}$ Ising model are analyzed by partial differential approximants. Series to order 21 in both $x\propto \frac{1}{T}$ and the interpolation parameter, $y$, yield unbiased estimates for the correction-to-scaling exponent, $\theta =0.54\mathrm{}\pm 5$, and the susceptibility exponent, $\gamma =1.2385\mathrm{}\pm 15$. The results are universal and agree tolerably with field-theoretic estimates and well with biased, one-variable analyses of general spin Ising models.

The relaxation function for a two-dimensional dense electron gas is obtained by solving the generalized Langevin equation due to Mori. The dynamic form factor, dynamic polarizability, and conductivity are calculated with use of linear response theory. The conductivity arises from density fluctuations existing at finite wave vectors. The possibility of observing such an effect is considered, especially in the recent work of Allen, Tsui, and DeRossa.

A microscopic calculation for the electron gas which is parameter free and satisfies the sum rules predicts twin peaks in the dynamic structure factor which are in substantial quantitative agreement with reported measurements on Be and Al. The twin peaks are generated by dynamic Coulomb correlations between pairs of electrons. No evidence is seen of a corresponding maximum in the pair correlation function.

A measurement of the mobility of a two-dimensional Wigner lattice supported by a liquid-helium surface is reported, and the results are compared with theory. The data exhibit a minimum in the mobility as a function of temperature. A narrow excess scattering peak located at or near the melting temperature is reminiscent of excess scattering associated with the dissociation of vortex-antivortex pairs two-dimensional helium films and superconductors. Quantum corrections to the melting curve are observed.