Characteristics of $W$ production are well described by a parton-shower approximation, based solely on the $q\overline{q}\to \mathrm{Wg}$ subprocess with a low-$p_T$ cutoff chosen to reproduce the total cross section through order ${\alpha }_s$. We apply this approach to $Q\overline{Q}$ production from the 2→ 3-parton subprocesses in $p\overline{p}$ collisions. The results agree with CERN dimuon events for a $B^0-{\overline{B}}^0$ mixing parameter $\epsilon \gtrsim 0.1$, which is at the $e^{+}{e}^{-}$ experimental limit and larger than standard-model expectations.

It is shown that spontaneous breakdown of parity within left-right-symmetric theories can be entirely responsible for generating a spontaneous breakdown of "isospin" symmetry leading to large up-down mass splitting within a family.

Duality invariance of the Dirac-Schwinger charge-symmetric theory for electromagnetism leads one to consider the invariant separation distances between the basic units of electric and magnetic charge. It is observed that equidistance between the quark and associated magnetic-monopole charges ($-\frac{e}{3}, 24\frac{\pi }{e}$) and ($2\frac{e}{3}, -12\mathrm{}\frac{\pi }{e}$) is equivalent to the condition $\left(\ln 9{\alpha }^{-1\mathrm{}}\right)\left(\ln 2\right)=\frac{1}{2}{\pi }^2$, which is indeed satisfied by the experimental value for $\alpha$ to within 0.027%. Conversely, the observed value for $\alpha$ follows to high accuracy from the postulate of duality-invariant equidistance between the basic units of electric and magnetic charge.

The signatures for horizontal-gauge-boson production at a $\sqrt{s}=40\mathrm{}$-TeV hadronic collider are studied. Production and decay of the boson leads to very massive lepton pairs (such as $e\mu$ or $\mu \tau$) in an otherwise quiet event, providing a clean signature. Backgrounds are studied with the Lund Monte Carlo model. The dominant background comes from $W^{+}{W}^{-}$ pairs, but there is good separation of the signal from the background. The identification of $\tau$ may be important for horizontal bosons; we note that the $\tau$ path lengths could be many tens of centimeters, suggesting new possibilities for their identification.

We compute the one-loop corrections to the Wess-Zumino Lagrangean governing ${\pi }^0$, ${\eta }_8\to \gamma \gamma$. The SU(3) relation between the two decay rates receives modifications of order $m_K^2\ln m_K^2$, as does the Gell-Mann-Okubo mass formula. A consistent picture of $\eta -{\eta }^{\prime }$ mixing emerges from both the two-photon widths and the mass matrix, however with a mixing angle $\theta \approx -20\mathrm{}°$ instead of the usual $\theta \approx -10\mathrm{}°$.

We present the first results from a small-lattice ($6^3$ × 10) calculation of nonleptonic weak matrix elements. The $\Delta I=\frac{1}{2}$ rule is studied as a test case. For a lattice meson of approximately the kaon mass we find a significantly enhanced $\Delta I=\frac{1}{2}$ amplitude and a $\Delta I=\frac{3}{2}$ amplitude compatible with zero within our statistics. The dominance of the $\Delta I=\frac{1}{2}$ amplitude appears to be due to a class of graphs called the eye graphs. Qualitatively similar results are found whether or not the charm quark is integrated out ab initio. We also report preliminary results on other weak matrix elements.

Hybrid stochastic differential equations are applied to the thermodynamics of lattice gauge theory with dynamical fermions. The tuned algorithm is much more efficient than pure Langevin or molecular-dynamics equations. The method is applied to quantum chromodynamics and the abrupt finite-temperature crossover between hadronic matter and the quark-gluon plasma is elucidated.

We discuss the low-energy effects of extra light $Z$ bosons in unified models especially in those models which might arise from the $E_8\otimes E_8^{\prime }$ superstring. We find that deviations from the standard model in neutral-current scattering data can give a very sensitive test of the presence of such bosons, of unification, and of the pattern of symmetry breaking. Such deviations have already in fact been observed. We also discuss flavor-changing effects such as $\mu \to 3e$.

Evidence for a three-nucleon absorption mechanism has been observed in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ for positive and negative pions of 220 MeV/c. The effect shows pure phase-space behavior with integrated cross sections of 3.9±0.5 mb for ${\pi }^{+}$ and 3.7±0.6 mb for ${\pi }^{-}$ absorption.

We treat the relativistic propagation of nucleons coupled to scalar- and vector-meson fields in a mean-field approximation. The time-dependent Dirac and mean-meson-field equations are solved numerically in three dimensions. Collisions of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(300, 600, and 1200 MeV/nucleon) + ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ are studied for various impact parameters. The results are compared to other recent theoretical approaches. The calculations predict spallation, large transverse-momentum transfer, and positive-angle sidewards flow, in qualitative agreement with the data in this energy regime.

The transmitted light from an optical cavity containing a single two-level atom may show photon antibunching and squeezing. The two effects are closely related and simply understood in terms of the theory of single-atom resonance fluorescence. It follows that corresponding nonclassical effects in optical bistability do not originate in atomic collectivity.

We have measured the distribution of times for single-mode laser radiation to grow from an equilibrium spontaneous-emission background to a prescribed value of the intensity. These passage-time distributions are compared with the results of Monte Carlo simulations and demonstrate a new technique for the description of statistical fluctuations in lasers.

We study an experimental orbit on a two-torus with a golden-mean winding number obtained from a forced Rayleigh-Bénard system at the onset of chaos. This experimental orbit is compared with the orbit generated by a simple theoretical model, the circle map, at its golden-mean winding number at the onset of chaos. The "spectrum of singularities" of the two orbits are compared. Within error, these are identical. Since the spectrum characterizes the metric properties of the entire orbit, this result confirms theoretical speculations that these orbits, taken as a whole, enjoy a kind of universality.

In quantum-beat and Hanle-effect experiments, spontaneous-emission events from two coherently excited states are strongly correlated. A doubly resonant laser cavity driven by such atomic configurations can have vanishing diffusion coefficient for the relative phase angle.

The first microscopic observation of a roughening transition on a crystal surface is reported. The surface involved is a so-called satellite face of a modulated ((C${\mathrm{H}}_3$)${}_4{}^{}{}_{}{}^{}\mathrm{N}$)${}_2{}^{}{}_{}{}^{}\mathrm{Zn}$${\mathrm{Cl}}_4$ crystal. The orientation of such a face is directly coupled to the length of the structural modulation wave vector q. At a change of q the stable satellite orientations change. Applying in situ optical microscopy we observed growth and etch features on the ($101\overline{2}$) satellite face; at the first commensurate-commensurate phase transition the roughening features suggest a sudden decrease of the edge free energy to zero.

A model of intercalation is presented which can be used for sophisticated three-dimensional computer simulations of staging kinetics. A realistic microscopic description of the intercalation process and of the stage-3 to stage-2 transition has been obtained for the first time. Stage disorder and three-dimensional effects are shown to be key ingredients of these phenomena. This work makes possible the first critical appraisal of the Daumas-Hérold model, which is shown to be valid for uniformly intercalated high- and low-stage crystals, and to provide a useful language for describing the stage transition.

Calculations have been made of inelastic-neutron-scattering cross sections for ferromagnetic iron. Quite unexpectedly, a rich picture of high-energy collective excitations has emerged. In particular, "optic" spin-waves modes with energies ranging to about 750 meV are predicted. Thus, iron is an ideal candidate for a novel high-energy-transfer experiment on recently developed high-energy neutron sources.

From transmission electron-energy-loss measurements we show that the mass of an exciton $M^{*}$ is greater than the sum of the effective masses of the electron and hole $m_e+m_h$. This result is consistent with a recent prediction by Mattis and Gallinar.

The dynamic coherence volume of the sliding-charge-density-wave conductor orthorhombic Ta${\mathrm{S}}_3$, obtained from the broad-band noise, is found to diverge as the threshold field is approached from above. In agreement with a recent theoretical treatment of the depinning process as a dynamical critical phenomenon, scaling behavior is observed for both this divergence and the charge-density-wave current. The apparent critical exponents for the coherence length and the charge-density-wave current differ substantially from the calculated mean-field values. Thermal rounding of the transition is observed at high temperatures.

A strong isotope effect has been found in field dissociation by atomic tunneling of He${\mathrm{Rh}}^{2+}$, which can be reasonably well accounted for with a WKB calculation. Field dissociation can occur only if the ion is rotated by 180° from its desorbed orientation to line up properly with the field. This rotation time of a ${}_{}{}^4{}_{}{}^{}\mathrm{He}$${\mathrm{Rh}}^{2+}$ ion in a field of ∼4.5 V/Å is determined to be 8 × ${10}^{-13\mathrm{}}$ s.