The Hamiltonian of the chiral-invariant Gross-Neveu model is diagonalized, without approximation, using a modified Bethe Ansatz.

The hypothetical existence of new color interactions, which participate in the spontaneous breaking of the weak-interaction group, will in general lead to relatively light composite pseudo Goldstone bosons. Their production and decay characteristics are analyzed to be close to, yet actually distinguishable from, those of the elementary Higgs bosons of the Weinberg-Salam model.

Experimentally observable consequences of a possible Bose-Einstein condensation of pions in energetic heavy-ion collisions are demonstrated. An excess of low-energy pions in recent data may indicate a Bose-Einstein-condensation-like phenomenon.

It is suggested that in a finite nucleus there may exist a condensed phase in which the spins of the protons are all aligned in one direction and the spins of the neutrons in the other and which has a lower energy than that of the normal phase above some density. It is found that this critical density is a few times larger than the normal density and that the nucleus will have a strongly oblate shape.

$K$-vacancy fractions have been measured for O ions moving in Fe and for F ions moving in Fe, Co, and Ni at velocities $2.1<~\frac{v}{v_0}<~10.5$. Discontinuities that explain those found for the transient magnetic field are observed. The present findings indicate that (i) the transient field cannot be approximated by a linear velocity dependence for $Z_1<~8$ in Fe and for $Z_1<~9$ in Co and Ni, and (ii) the discontinuity in the transient field is only present at velocities below $4v_0$.

Two pronounced dips in the ${\mathrm{H}}^{-}$ photodetachment cross section have been observed at photon energies of 12.650±0.004 and 12.837±0.004 eV, just below the hydrogenic $n=3\mathrm{}$ threshold. These energies were reached by crossing a uv laser beam with a relativistic ${\mathrm{H}}^{-}$ beam. The dips are interpreted as the first two members of a ${}_{}{}^1{}_{}{}^{}P$ Feshbach resonance series, of the "+" type, converging on $n=3\mathrm{}$. Fano line shapes have been fitted to these structures to extract their intrinsic widths and line profile indices.

We have made the first observation of the vibrational-rotational spectrum of the electronic ground state of the helium-hydride molecular ion ${}_{}{}^4{}_{}{}^{}\mathrm{He}$${\mathrm{H}}^{+}$. The Doppler-tuned ion-beam laser-spectroscopic technique was used. The frequencies of five transitions between 1700 and 1900 ${\mathrm{cm}}^{-1\mathrm{}}$ have been measured to ± 0.002 ${\mathrm{cm}}^{-1\mathrm{}}$ (±1 ppm). The experimental values deviate from current theory by typically 0.2 ${\mathrm{cm}}^{-1\mathrm{}}$, and are two orders of magnitude more precise than the theoretical values.

Radiation from 56- and 28-MeV electrons channeled along major plances or along a major axis of an 18-μ-thick silicon crystal has been observed. Unpredicted spectral peaks in the range from 10 to 130 keV were observed and resolved for planar-channeling electrons, whereas only a large low-energy enhancement was seen for axial-channeling electrons.

By using a new, delayed-heterodyne photon-echo technique, we have obtained a spectral resolving power of 1.2×${10}^{11}$, measuring a 2.0-kHz linewidth (half width at half maximum) for the 6105-Å ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}\leftrightarrow {}_{}{}^3{}_{}{}^{}H_4^{}{}_{}{}^{}$ transition of YAl${\mathrm{O}}_3$: ${\mathrm{Pr}}^{3+}$ in an external magnetic field. This appears to be the highest resolution ever obtained in optical spectroscopy. Measurements were also made on the corresponding transition of La${\mathrm{F}}_3$: ${\mathrm{Pr}}^{3+}$ giving a linewidth of 5 kHz. Optical free induction decay gave incorrect results (i.e., significantly broader linewidths).

The presence of superbanana orbits localized to either the interior or the exterior of classical stellarators and torsatrons is investigated for 3.5-MeV $\alpha$ particles. The absence of the interior superbanana in both geometries is found to be related to nonconservation of the action. Exterior superbananas are found in the stellarator only, as a consequence of the existence of absolute localized magnetic wells. No superbananas of either type are found in the torsatron.

Pressure jump experiments have been performed to study the relaxation of isobutyric acid and water mixtures to equilibrium states in the one-phase region near a critical point. Small-angle light-scattering measurements have been used to monitor the aproach to equilibrium. The observed time dependence of the scattered intensity is in good agreement with a model proposed by Binder.

The internal energy and the order parameter of the three-state Potts model in a simple cubic lattice are calculated using the Monte Carlo technique. Both properties exhibit metastabilities in a small temperature region demonstrating that the phase transition is of first order. This result is in agreement with the prediction of the $\epsilon$ expansion but in contrast to the position-space renormalization-group calculations which lead to a continuous transition.

Second sound in the $A_1$ phase of superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ has a velocity three orders of magnitude larger than in the $A$ phase and is at the same time a spin wave. A magnetic field inhomogeneity leads, depending on the geometry, either to a pressure or temperature difference. These results, among others, contradict predictions by previous authors and are obtained from the hydrodynamic theory derived in this Letter by employing the concept of broken relative symmetry.

It is shown that the nonlinear dynamics of anharmonically interacting particles in the presence of periodic fields leads to a set of cascading bifurcations into a chaotic state. This state is characterized by the existence of a strange attractor in phase space and associated broadband noise in the spectral density. It is suggested that solid-state turbulence is likely to be found in weakly pinned charge-density-wave systems and superionic conductors.

New neutron-diffraction measurements on single crystals of Ce${\mathrm{Al}}_2$ confirm the previously reported incommensurate antiferromagnetic ground state with peaks at ${\overrightarrow{\mathrm{q}}}_I=(\frac{1}{2}\pm \alpha ,\frac{1}{2}\mp \alpha ,\frac{1}{2})$. In addition, weaker superlattice peaks are observed at ${\overrightarrow{\mathrm{q}}}_c=(\frac{1}{2},\frac{1}{2},\frac{1}{2})$ and their position and temperature dependence can be explanined in terms of a multiple-$q$ structure in Ce${\mathrm{Al}}_2$. This appears to be the first definitive evidence for a multiple-$q$ magnetic structure.

Magnetic resonance transitions of muonium in quartz have been detected by their effect on muon-spin-rotation frequency spectra. This technique can be used to observe EPR transitions which are not directly observable in the normal muon-spin-rotation spectrum. The coherence effects of an intense rf magnetic field on two strongly coupled spins are decribed theoretically and are found to explain the data in detail.

This Letter shows that in the mean-field approximation spin-glasses must be described by an infinite number of order parameters in the framework of the replica theory.

Angle-resolved photoemission spectra of Au(100)-(1×1) and -(5×20) surfaces were obtained for the $\Gamma \mathrm{LUX}\Gamma$ and $\Gamma \mathrm{XWK}\Gamma$ mirror planes of the bulk Brillouin zone. Peaks were observed, which can be removed by changing the surface order, and were attributed to surface states near symmetry points of the corresponding surface Brillouin zones. Other emission peaks, attributed to bulk transitions show drastic changes in intensity for different surface order.

For rare-earth elements having two different $4f$ configurations in the same material, $3d$ and $4d$ core-level photoemission spectra will exhibit two sets of structures, or replicas, each corresponding to one of the $4f$ configurations. Our estimates of the positions of these structures agree with the available data and suggest the utility of replicate core levels as a useful probe of valence-fluctuation materials.

A close connection between Griffiths-Pearce "peculiarities" in position-space renormalization-group transformations and singularities in the free energies of systems with quenched random fields is pointed out. For a large class of weight functions the recurrence relations for the coupling constants of a nonrandom Ising system exhibit singularities where there is a phase transition in a related system with a random field.