A very simple system with quasiperiodic dynamics is introduced, consisting of a single spin, with spin ½, in a pulsed magnetic field. The pulses are of two types, and the two types alternate in a quasiperiodic way. By adapting renormalization-group and dynamical-systems techniques first introduced in the study of one-dimensional quasiperiodic structures, I characterize the long-time behavior as a function of the experimental parameters. Within different well-defined regions of parameters space, the time correlations decay (a) more slowly than a power law, (b) as a power law, or (c) faster than a power law, and probably exponentially.

Cross sections for the charged-current interactions of ultrahigh-energy neutrinos with nucleons are evaluated in light of recent improvements in our knowledge of nucleon structure functions. For ${10}^{19}$-eV neutrinos, the cross section is an order of magnitude larger than the values traditionally used in astrophysical calculations. Some consequences for event rates from generic astrophysical neutrino sources are noted.

Finite-temperature behavior of quantum chromodynamics is investigated with the Langevin technique including the dynamical quark loops. The deconfining and chiral transitions occur at the same temperature. The strength of transition weakens initially as the quark mass decreases from infinity, but at small quark masses it strengthens again and shows the characteristic of a first-order transition. We estimate the inverse coupling constant at zero quark mass to be ${\beta }_c=\frac{6}{g_c^{}{}_{}{}^2}\simeq 4.9-5.0$ for four flavors on an $8^3$ × 4 lattice.

We measured the analyzing power $A$ and the spin-spin correlation parameter $A_{\mathrm{nn}}$, in large-$P_{\perp }^2$ proton-proton elastic scattering, using a polarized-proton target and the polarized-proton beam at the Brookhaven Alternating-Gradient Synchrotron. We also used our polarimeter to measure $A$ at small $P_{\perp }^2$ at 13 GeV with good precision and found some deviation from the expected $\frac{1}{P_{\mathrm{lab}}}$ behavior. At 18.5 GeV/c we found $A_{\mathrm{nn}}=(-2\mathrm{}\pm 16)\%$ at $P_{\perp }^2=4.7\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. Comparison with lower-energy data from the Argonne Zero-Gradient Synchrotron shows a sharp and surprising energy dependence for $A_{\mathrm{nn}}$ at large $P_{\perp }^2$.

We show that the Feynman rules in the covariant $\alpha$ gauge, the Coulomb gauge, and the axial gauge, in the generally adopted form derived via the Faddeev-Popov formalism, are inconsistent with one another. We suggest that they be replaced by the canonically derived ones, which are consistent. In particular, the Feynman rules in the Coulomb gauge contain the contribution of the anomalous Coulomb interaction, and the Feynman rules in the axial gauge with the principal-value prescription contain the contribution of ghost loops.

The possibility of soliton states, resembling skyrmions, occurring in a hypercolor framework of the electroweak theory is discussed. This is done with a renormalizable linear-sigma-model realization of the soliton which may allow for new structure not far above the $W$ and $Z$ bosons in mass.

We present a first quantization of the space-time embedding $X^{\mu }$ and the world-sheet metric $\rho$ of the open bosonic string. The world-sheet metric $\rho$ decouples from $S$-matrix elements in 26 dimensions. This formulation of the theory naturally includes 26-dimensional gauge transformations. The gauge invariance of $S$-matrix elements is a direct consequence of the decoupling of $\rho$. Second quantization leads to a string field $\Phi [X^{\mu },\rho ]$ with a gauge-covariant equation of motion.

Large-$N$ arguments suggest that baryons correspond to soliton solutions of the optimal lowenergy Lagrangean of QCD. Such solitons are characterized by a hedgehog symmetry which mixes isospin and space rotations. We show that this symmetry implies linear relations between experimental $\overline{K}N$ and $\pi N$ elastic partial-wave scattering amplitudes. At least in one case these linear relations are satisfied with an extremely high accuracy.

The branching ratios for ${\tau }^{-}\to {\pi }^{-}{\pi }^{-}{\pi }^{+}{\nu }_{\tau }$ and ${\tau }^{-}\to {\pi }^{-}{\pi }^{-}{\pi }^{+}\left(n{\pi }^0\right){\nu }_{\tau }$, $n>~1$, have been measured to be 0.078 ± 0.005 ± 0.008 and 0.047 ± 0.005 ± 0.008, respectively. The total three-prong tau branching ratio is 0.128 ± 0.005 ± 0.008. Study of the $3{\pi }^{\pm }{\nu }_{\tau }$ decay indicates that the three pions are predominantly from a $J^P=1^{+}$ state which decays through a ${\rho }^0{\pi }^{\pm }$ intermediate state in a relative $s$ wave. The $\rho \pi$ mass spectrum is suggestive of a resonance.

A phenomenological model is presented which can explain all aspects of the observations of undergound muons associated with Cygnus X-3. A long-lived, light neutral particle produced at Cygnus X-3 interacts in the earth with a cross section in the range 10 to 20 μb. This interaction produces a massive secondary particle with mass 10 to 40 GeV/${\mathit{c}}^2$, which decays to at least one muon. It is possible that the primary particles are produced hadronically at Cygnus with a very small cross section.

Inspired by the possible particle content of the heterotic superstring at low energies, a model is proposed where the $b$ quark is not paired with the $t$ quark. Instead, the $b$ quark couples to the $c$ quark through a second $W$ boson. This model is consistent with all established experimental and phenomenological constraints, and predicts the mass of the second $W$ boson to be just beyond the experimental limit of about 400 GeV.

The Landau theory of shape transitions in hot rotating nuclei is introduced and the universal features of such transitions are derived. The phase diagram of the excitation energy versus angular momentum $J$ for nuclei with prolate ground states shows a transition line from triaxial to oblate shapes. The transition is first order for small values of $J$ and becomes second order above a certain value which is the analog of the tricritical point. Nuclear shapes change very rapidly from near prolate to oblate in the vicinity of this point. The theory is used to calculate the phase diagram of the ${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}$ nucleus.

$\pi -{}_{}{}^4{}_{}{}^{}\mathrm{He}$ inelastic cross sections have been measured at $T_{\pi }=180\mathrm{}$ MeV. In the region of the $J^{\pi }=1^{-}$ states $E_x\simeq 23 \mathrm{to} 30$ MeV) the $\frac{{\pi }^{+}}{{\pi }^{-}}$ cross-section ratio $R_{\pi }$ was found to be 1.05 ± 0.08 at ${\theta }_{\mathrm{lab}}=30\mathrm{}°$. Such a small deviation from 1.0 implies that isospin mixing between the $T=0\mathrm{}$ and $T=1\mathrm{}$ states in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is quite weak, in striking contrast to the strong isospin mixing deduced from the large ratio of photonucleon cross sections, $R_{\gamma }=\frac{\sigma (\gamma ,p)}{\sigma (\gamma ,n)}\simeq 1.7$. Thus the conclusion drawn from the photonucleon work, that there is a large charge-symmetry-breaking nuclear force in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, needs to be reexamined.

We demonstrate that the charge-distribution differences between isotopes of heavy-mass nuclei are the most sensitive experimental quantities for extraction of the compression modulus of nuclear matter. This analysis shows a compression modulus larger than 200 MeV.

High-angular-momentum components have been found in the cross section for ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ + ${}_{}{}^{92}{}_{}{}^{}\mathrm{Zr}$ → ${}_{}{}^{156}{}_{}{}^{}\mathrm{E}\mathrm{r}*$ by $\gamma$-ray spectroscopy. They are expected to influence the known low evaporation-neutron multiplicity. The feeding pattern rules out significant trapping in superdeformed states at low spin, an explanation previously advanced. Simple coupled-channels calculations are consistent with the observations. The statistical model with high-$l$ fusion enhanced consistently with observation reproduces the neutron multiplicity satisfactorily.

Energy and angular distributions were measured for high-energy ($E_{\gamma }>10\mathrm{}$ MeV) gamma rays from collisions of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ on Pb, Zn, and C at beam energies of $\frac{E}{A}=20, 30, \mathrm{and} 40$ MeV. The gamma-ray energy spectrum was measured to about 120 MeV at $\frac{E}{A}=40\mathrm{}$ MeV and to about 80 MeV at $\frac{E}{A}=20\mathrm{}$ MeV. For $E_{\gamma }>20\mathrm{}$ MeV the spectra are roughly exponential with characteristic slope parameters ranging from 10.0 MeV for ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ + Pb at $\frac{E}{A}=20\mathrm{}$ MeV to 14.2 MeV at $\frac{E}{A}=40\mathrm{}$ MeV. Reasonable agreement is obtained with a model employing bremsstrahlung from individual neutron-proton collisions in the heavy-ion collision.

The sign of the average emission angle of nonequilibrium light particles was determined from the circular polarization of coincident $\gamma$ rays emitted from residual nuclei for ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$-induced reactions on ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$ at $\frac{E}{A}=20\mathrm{} \mathrm{and} 35$ MeV. Light particles ($p,d,t,\alpha$) are preferentially emitted to negative angles. This effect is consistent with deflection of the particles by the attractive nuclear mean field. Numerical solutions of the Boltzmann-Uehling-Uhlenbeck equation demonstrate that the experimental result is sensitive to the interplay between the nuclear mean field and nucleon-nucleon collisions.

Muon-channeling profiles resulting from the decay of positive pions implanted in high-purity Ge and GaAs single crystals with and without illumination have been measured. The change in profiles with illumination demonstrates that the pion decay site is sensitive to the concentration of excess charge carriers produced by photon absorption. This site change is explained in terms of different electronic states of the pion, i.e., bare ${\pi }^{+}$ and pionium.

A high-precision laser optical-pumping experiment on the ${}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ ground state of atomic rubidium in magnetic fields of up to 8 T has led to the first observation of a magnetically induced quadrupole hyperfine interaction, in both ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ and ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$. The quadrupole coupling constant was measured to be 7.0(6) × ${10}^{-4\mathrm{}}$ Hz ${\mathrm{T}}^{-2\mathrm{}}$ in ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$. The diamagnetic shift in dipole hyperfine structure was also measured in both ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ and ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$. The fractional dipole shift was found to be independent of isotope with a value $\frac{\delta a}{a}=5.2\mathrm{}\left(2\right)\mathrm{}\times {10}^{-10\mathrm{}}$ ${\mathrm{T}}^{-2\mathrm{}}$, confirming and extending previous results for ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ only.

On the basis of exact quantum mechanical calculations we study energy-level spectra and photoabsorption cross sections for a hydrogen atom in a uniform magnetic field. In the classically chaotic region near the threshold the level distributions show the irregular pattern predicted by randommatrix theories; on the other hand, the photoabsorption spectra show not only the traditional quasi-Landau modulations but also new and unexpected modulations which may be related to classical periodic orbits embedded in a chaotic system.