A closed-form expression is proposed for the critical frontier, or the critical line, of the antiferromagnetic Ising model on the honeycomb lattice in a nonzero external magnetic field. We formulate the Ising model as an 8-vertex model and identify the critical frontier as a locus invariant under a generalized weak-graph transformation. In its simplest form the locus is an expression containing two unknown constants which we determine numerically. The resulting critical frontier lies very close to results of a finite-size analysis.

A method is described for obtaining numerical solutions of the pulsation equations of rapidly rotating inhomogeneous stellar models. This previously intractable problem has been solved by reexpressing the pulsation equations in terms of a single potential. These equations are solved and the points of the onset of secular instability to gravitational radiation are found. These results indicate that the 0.5-ms period of SN 1987A cannot be interpreted as the rotation of a neutron star using current descriptions of neutron-star matter.

We show that the decay of a scalar particle into ordinary matter particles is restricted by the mass and by the vacuum expectation value of the scalar field. If this scalar field is responsible for inflation, difficulties with reheating the Universe may ensue. For the case of induced-gravity models, where the magnitude of the vacuum expectation value is of order the Planck mass, the scalar field decays predominantly into gravitons and adequate reheating does not occur in the usual slow rollover scenario. We also discuss the effect of the energy stored in the scalar-field oscillations.

In the Chern-Simons gauge theory on a manifold $T^2$×$R^1$ (two-torus×time) the unitary operators, which induce large gauge transformations shifting the nonintegrable phases of the two dinstinct Wilson-line integrals on the torus by multiples of 2π, do not commute with each other unless the coefficient of the Chern-Simons term is quantized. In U(1) theory this condition gives the statistics phase θ=π/n (n an integer). The condition coincides with the one previously derived on a manifold $S^3$ (three-sphere) for SU(N≥3) theory but differs by a factor 2 for SU(2) theory. The requirement of the $Z_N$ invariance in pure SU(N) gauge theory imposes a stronger constraint.

We present an electroweak theory in which left-handed quarks and leptons transform as doublets under separate SU(2) gauge groups. Spontaneous symmetry breakdown results in two charged and two neutral massive vector bosons. The lightest charged and neutral gauge bosons behave like the W and Z of the standard SU(2)×U(1) electroweak model. The heavier W and Z, which can be as light as several hundred GeV, couple primarily to quarks. Our theory predicts small deviations in the properties of the Z which will be visible at the SLAC Linear Collider and the CERN collider LEP.

Renormalization-group equations and asymptotic conditions are used to obtain top-quark mass predictions. In the standard model with an explicit Higgs mechanism, our analysis becomes identical to the Kubo-Sibold-Zimmermann coupling-reduction approach. Refining their prediction, we find $m_t$≃95 GeV. In the simplest case of self-consistent dynamical symmetry breaking, we obtain $m_t$≃115 GeV. An illustration of how short-distance new physics can alter these predictions is given.

CP-violating asymmetries in the B→Kφ decays are studied in the four-generation model. The absorptive part in the penguin amplitude leads to the CP-violating asymmetry in the $B_U^{\pm }$→$K^{\pm }$φ decays, which could be as large as ±15% in the four-generation model, although it is at most a few percent in the three-generation model. The asymmetry between the $B_d^0$→$K_S^0$φ and B${¯}_d^0$→$K_S^0$φ decays is also expected to be ±10% on Υ(4S) through the penguin absorptive part with the contribution of the fourth-generation quark.

Pseudorapidity distributions of relativistic singly charged particles in oxygen-induced emulsion interactions at 14.6, 60, and 200 GeV/nucleon are studied. Limiting fragmentation behavior is observed in both the target and projectile fragmentation regions for a central as well as for a minimum-bias sample. Comparisons with the fritiof model reveal that the picture of fragmenting strings successfully describes the observed data.

The structure in the β-delayed proton spectra of the precursors ${}_{{}_{66}{}^{147}{}_{}{}^{}}{}^{}{}_{}{}^{}\mathrm{Dy}_{}^{\mathrm{g}}{}_{}{}^{}$, ${}_{{}_{68}{}^{149}{}_{}{}^{}}{}^{}{}_{}{}^{}\mathrm{Er}_{}^{\mathrm{g}}{}_{}{}^{}$, and ${}_{{}_{70}{}^{151}{}_{}{}^{}}{}^{}{}_{}{}^{}\mathrm{Yb}_{}^{\mathrm{g}}{}_{}{}^{}$ is analyzed within the framework of a doorway-state model. Indications from γ-ray decay studies, β strength-function measurements, and calculations of state densities and Gamow-Teller strength distributions, lead us to suggest that some of the observed proton transitions arise from the preequilibrium decay of doorway states populated in ${\beta }^{+}$ decay or electron capture.

We report measurements of the lifetimes of the $2^1$${\mathrm{S}}_0$ state of heliumlike ${\mathrm{Ni}}^{26+}$ and the $2^2$${\mathrm{S}}_{1/2}$ state of hydrogenlike ${\mathrm{Ni}}^{27+}$, both of which decay predominantly by two-photon emission. Our method differs from previous measurements of the lifetimes of similar states in that we require a coincidence between the two photons. Our lifetime of 217.1(1.8) ps for the hydrogenlike decay is in agreement with the theoretical value of 215.45 ps. The heliumlike decay lifetime of 156.1(1.6) ps is in fair agreement with the theoretical value of 154.3(0.5) ps.

A single lasing mode driven by a three-level ‘‘quantum-beat’’ atomic configuration can show gain without population inversion or optical absorption into an excited state without spontaneous or stimulated emission.

The effect of multiple electron excitation on the threshold behavior of Xe 5s photoionization is studied using the multichannel multiconfiguration Dirac-Fock method with full account of relaxation. The inclusion of the ionization channels related to 5${\mathrm{p}}^4$5d ${\mathrm{J}}_{\mathrm{ion}=(1/2\mathrm{}}$ excited states is found to change the single-excitation results drastically. Our cross section and asymmetry parameter β are in very good agreement with experiment. Calculation of the related satellite cross sections predicts a new type of satellite that exists only in the near-threshold region and has a peculiar angular dependence.

The first studies with the hydrogen atom in strong crossed magnetic and electric fields are reported. Long-living states reaching well above the Stark saddle energy are discovered. They are quantitatively explained by second-order perturbation theory, indicating regular, nonchaotic dynamics in these states. Fourier-transformed spectra and classical trajectory calculations indicate the existence of periodic orbits high in the field ionization regime. Sensitive spectral dependence upon the angle between the fields due to symmetry breaking is observed and accounted for by second-order perturbation theory.

Using digital subtraction radiography, we study the basic modes of a granular material (here sand) flowing through a flat hopper. These modes take the form of density waves whose formation and propagation is controlled by several parameters, including the mass flow rate M and the hopper angle θ. We consider the effect of roughness on pattern formation in this system using mixtures of smooth and faceted sand and show the existence of a bifurcation at a mass fraction of faceted sand X≊0.2. Propagating patterns form in faceted sand but not in smooth sand of the same size.

The first experimental evidence of modification of the scattered light spectrum of stimulated Raman scattering due to the presence of significant levels of stimulated Brillouin scattering is presented. The observed spectrum, as well as the spectral Raman gap observed in this and other experiments, is explained in terms of the modified growth of Raman in the presence of ion waves.

A ${\mathrm{D}}_2$O far-infrared laser emitting 0.5J in 1.4 μs at 385 μm and a heterodyne receiver system comprising a Schottky barrier diode mixer with a noise temperature of 8000° K (double sideband) were used in a Thomson scattering experiment to measure the ion temperature of a tokamak plasma during a single laser shot. Series of measurements under reproducible plasma conditions have been carried out in hydrogen, deuterium, and helium plasmas. Their statistical analysis yielded a typical relative error of 25% for a single shot measurement.

Highly collimated plasma jets are produced with laser irradiation of solid barium targets. The plasma streams many Larmor radii across a strong transverse magnetic field (10 kG) with little inhibition. The plasma jet is observed to narrow or ‘‘focus’’ in the plane perpendicular to the field, while in the plane of the field the plasma expands along the field lines and displays flutelike striations. The narrowing of the plasma jet is understood in terms of the configuration of the plasma polarization fields while the flute structure is identified as a electron-ion hybrid velocity-shear instability.

Scaling in late-stage spinodal decomposition is discussed using standard renormalization-group techniques. The equal-time correlation function has the scaling form C(r,t)=f(r/$t^{1/z}$), with z=d+2-y, where z and (-y) are, respectively, the dynamical exponent and thermal eigenvalue for the zero-temperature fixed point and d is the spatial dimensionality. For a scalar order parameter, y=d-1 gives z=3, implying a domain growth law L(t)∼$t^{1/3}$. For a vector order parameter, y=d-2 gives z=4 and L(t)∼$t^{1/4}$.

Random walks and ideal chains (equally weighted trajectories) on self-similar structures are shown to have, in specific examples, drastically different asymptotic behavior. In certain instances localization effects let the end-to-end distance of an ideal chain of length n grow like exp[αlogn${)}^{\phi }$] (φ<1) or (logn${)}^{\psi }$ for large n. The renormalization-group analysis and the fixed point, giving these behaviors, are of a new type. These results could be of experimental relevance for the migration properties of excitations on fractal structures in the presence of a trapping environment.

By probing the Ni content of Zr crystallites as a function of milling time using Auger spectroscopy, we report the first direct measurements of the interdiffusion which takes place during the amorphization of Ni-Zr by the mechanical alloying of pure-metal powders. Based on the concentration variation of Ni in Zr as a function of the milling time and using a simple interdiffusion model, we can estimate an effective local temperature at the collision site.