Compactification to four dimensions of a low-energy approximation to ten-dimensional O(32) string theory leads only to grand unified theories with trivial replication of families. The E(8) ⊗ E(8) string is more promising and leads in four dimensions to SU(8) with six families. If compactification breaks the symmetry to lower-rank groups, e.g., SU(7) or E(6), there may be any number of families. In the SU(8) and SU(7) models there is nontrivial family symmetry.

A search in $e^{+}{e}^{-}$ annihilation for final states which contain only a single energetic photon has been performed at $\sqrt{s}=29\mathrm{}$ GeV with the MAC detector at PEP. The upper limit on an anomalous signal has been interpreted in terms of mass limits for supersymmetric particles under the assumption of radiative pair production of either supersymmetric photons or neutrinos. For the supersymmetric electron ($\tilde{e}$) this limit is $m_{\tilde{e}}>37\mathrm{}$ GeV/${\mathit{c}}^2$ at the 90% confidence level if $m_{{\tilde{e}}_L}=m_{{\tilde{e}}_R}$ and the supersymmetric photon ($\tilde{\gamma }$) has $m_{\tilde{\gamma }}=0\mathrm{}$.

The formation of the quark-gluon plasma in relativistic nuclear collisions may be determined by enhanced production of $\phi$ mesons. This enhancement would result from the absence of the Okubo-Zweig-Iizuka suppression which inhibits $\phi$ production in ordinary $p-p$ and $\pi -p$ collisions, and from a large abundance of strange quarks in the plasma. The $\phi$ will not rescatter significantly in the subsequent expanding hadronic phase and would thereby retain information on the conditions of the hot plasma.

We propose a description of asymmetric shapes in nuclei in terms of a bosonic U(16) group, and discuss some properties of rotation-vibration spectra in the SU(3) limit of the model.

The tensor analyzing power $T_{20}$ for the radiative capture reaction ${}_{}{}^1{}_{}{}^{}\mathrm{H}(d_{\mathrm{pol}}, \gamma ){}_{}{}^3{}_{}{}^{}\mathrm{He}$ has been measured in order to test new three-body wave functions. This observable arises from the $D$ state of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. An effective two-body direct-capture calculation, which was previously shown to fit the $a_2$ coefficient of a Legendre-polynomial expansion of the differential cross section, is found to give a good description of the present data. A value for the asymptotic $\frac{D}{S}$ ratio is extracted from the data although it is found to be model dependent.

Band crossings are observed in the yrast $\alpha =-\frac{1}{2} \mathrm{and} +\frac{1}{2}$ negative-parity decay sequences in ${}_{}{}^{157}{}_{}{}^{}\mathrm{Ho}$ at $\hslash \omega =0.48\mathrm{} \mathrm{and} \approx 0.54$ MeV, respectively. These band crossings are interpreted as the alignment of the second and probably the third pair of $h_{\frac{11}{2}}$ quasiprotons. This is the first identification of delayed crossings involving the second aligning nucleon. These crossings show that sizable proton-pair correlations must remain for these configurations up to high rotational frequencies $\hslash \omega \approx 0.5$ MeV.

A dispersion relation is used to show that the "anomalous" behavior of the real part of the optical potential for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ scattering at low energies is an example of a general property of heavy-ion optical potentials at energies approaching the top of the Coulomb barrier, where the flux into nonelastic channels is drastically reduced.

We apply the new variational principle of Balian and Veneroni to calculate the fluctuations in final-fragment mass, charge, and kinetic energy for the systems ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ($E_{\mathrm{lab}}-160\mathrm{}$ MeV) and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ + ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ ($E_{\mathrm{lab}}=278\mathrm{}$ MeV). The calculated fluctuations are larger than conventional time-dependent Hartree-Fock results and, in the latter case, are consistent with the experimental fragment mass distribution.

The Xe $L_3-M_4{M}_5 \left({}_{}{}^1{}_{}{}^{}G_4^{}{}_{}{}^{}\right)$ Auger spectrum, photoexcited in the vicinity of the $L_3$ edge, has been measured as a function of photon energy. The $\mathrm{nd}$ spectator-electron satellite lines show resonant behavior. The diagram line exhibits the larges (≳ 1 eV) post-collision interaction shift yet observed. For comparison with the data, the first fully quantum-mechanical calculation of the post-collision interaction in deep inner-shell Auger decay is performed, based on a resonant-scattering approach that involves a complete summation over intermediate $L_3$ one-hole states.

Photocurrent yield and absorption spectra for xenon were measured as functions of pressure ($p<~1\times {10}^5$ Pa) between ∼11.0 and 11.8 eV. With a pressure-independent yield function $Y\left(h\nu \right)$ the photocurrent spectra can be calculated from the absorption spectra with the assumption of a "dead layer" at the surface of the LiF window. $Y\left(h\nu \right)$ is roughly proportional to the number of atomic transitions with excitation energies between 11.10 eV and $h\nu$. This behavior can be explained with a simple statistical model for the decay of the Rydberg states.

We present experimental data for the scattering of low-energy electrons from potassium at extremely small atomic scattering angles (of the order of ${10}^{-4\mathrm{}}$ rad) within the shadow of the atom beam. These data show an oscillatory structure which cannot be accounted for in the usual planewave description of the scattering. We suggest an explanation of these results in which the observed oscillations are due to an interference between the incoming and scattered beams.

The electronic part of a possible $P$- and $T$-nonconserving neutral-weak-current-induced electric dipole moment in atomic Xe and Hg was calculated with many-body perturbation theory. After the effects of this $P$- and $T$-nonconserving interaction on all core orbitals were treated self-consistently, thereby including all single-particle effects to all orders but no correlation effects, the results ${\mu }_e=(5.2\mathrm{}\times {10}^{-23\mathrm{}}e \mathrm{m})C_T{\sigma }_N$ and ${\mu }_e=-(6.0\mathrm{}\times {10}^{-22\mathrm{}}e \mathrm{m})C_T{\sigma }_N$, respectively, were obtained for Xe and Hg. The value for Xe can be combined with the recent experimental result, $\left|{\mu }_e\right({}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}\left)\right|<\mathrm{}{10}^{-28\mathrm{}}e \mathrm{m}$, to give the upper limit $\left|C_T\right|<\mathrm{}2\mathrm{}\times {10}^{-6\mathrm{}}$.

The alignment of the $4d^{9}5s^2{}_{}{}^2{}_{}{}^{}D_{\frac{5}{2}}^{}{}_{}{}^{}$ state of ${\mathrm{Cd}}^{+}$ is obtained from fluorescence polarization measurements using dispersed synchrotron radiation in the spectral region 680 to 710 Å. This region is dominated by strong autoionization features associated with the $nf\left({}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}\right)$ and $np({}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}, {}_{}{}^3{}_{}{}^{}D_1^{}{}_{}{}^{})$ Rydberg states converging to the $4d^{9}5s^2{}_{}{}^2{}_{}{}^{}D_{\frac{3}{2}}^{}{}_{}{}^{}$ fine-structure threshold. The polarization and alignment data show marked variations across the resonance profiles and are compared with recent calculations in the relativistic random-phase approximation in conjunction with multichannel quantum-defect theory.

A theoretical analysis of lower hybrid wave generation by a ring distribution of superthermal ions is presented. A kinetic instability of waves traveling across the magnetic field occurs when fast neutrals escaping from the Io plasma torus are reionized and accelerated to corotation speed in Jupiter's magnetosphere. Instability is possible for modest threshold vaules of $\frac{V}{a_0}=3-7\mathrm{}$ where $V$ is the pickup gyrospeed and $a_0$ is the background-ion thermal speed. Consequent effects include the relaxation of the pickup-ion distribution and the acceleration of superthermal electrons.

Excitation of electron plasma waves in a hot and fully ionized plasma by two laser beams is presented. The growth time and absolute amplitude of the excited waves, measured by light scattering, indicate very strong coupling of the laser light with the plasma.

The generation of microwaves from interacting vortices formed in thin magnetized electron beams is investigated experimentally and with three-dimensional electromagnetic particle simulations. Fine-detail photographs of relativistic and nonrelativistic beams show that vortex formation transcends 12 orders of magnitude in beam current. The simulations show a burst of microwave radiation from a rapid magnetic line connection and breaking between vortices when the vortex structure is well defined.

We report on the first comparison of the inelastic cross section of Ni(001) surface phonons for an extended energy range with a dynamical scattering theory. Both theory and experiment indicate large modulations in the loss cross section as a function of incident energy. The intensity ratio of the $S_4$ and $S_6$ surface phonons on Ni(001) is best fitted with a 1.7%-3.3% contraction in the outer-most interlayer spacing.

If a fluid mixture is periodically driven through its critical point, two distinct regimes are observed by light scattering. In one, the system ultimately approaches a meniscus-free state, and in the other, phase separation finally occurs. We focus attention on differing scaling forms of the structure factor in these two regimes and on the unexpectedly strong concentration fluctuations which are present in the disordered-phase state. Mean-field behavior is seen in this system.

We have observed a new magnetic field dependence to the thermal boundary resistance between liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and finely powdered silver particles. At a temperature of 1 mK we find the thermal boundary resistance to increase by nearly an order of magnitude as the magnetic field is raised from 0 to 200 mT. This behavior cannot be explained by conventional acoustic models of the heat conduction. By contrast, however, we observe no field dependence from 0.2 to 9.4 T, in strong contradiction to the behavior expected based on the recent conduction model of Perry et al.

A striking nonlinear transport behavior has been observed in the recently discovered high-magnetic-field phase of graphite. The phenomenon is reminiscent of the collective charge-density-wave transport observed in some classes of linear-chain compounds such as Nb${\mathrm{Se}}_3$. This supports our identification of the new phase with a charge-density-wave state. The principal direction of the charged-density wave vector is perpendicular to the magnetic field in contrast to the prediction of the Yoshioka-Fukuyama theory.