By constructing a complete set of coherent states that forbids double occupancy, we introduce a quantum Monte Carlo algorithm for simulation of fermion models with constraint, including the infinite-U Hubbard model and the t-J model. Application to the infinite-U Hubbard model on 4×4 and 6×6 lattices provides new physical results on the thermodynamics of the model, especially the temperature and doping dependence of the Nagaoka state.

Recent Brillouin scattering experiments have revealed the surprising existence of two acoustic modes in colloidal suspensions of solid spheres. Through an analytic Green’s-function calculation and numerical simulations, we show that the higher-frequency mode is associated with the solid-sphere antiresonances, and the lower-frequency mode arises from the coupling of internal resonances between neighboring spheres. Our theory yields excellent agreement with the measured dispersion relations and offers an explanation for the observed frequency gaps in the excitation spectra.

It is shown that the Peccei-Quinn mechanism will, in the large-N limit, remove dimension-six CP-violating operators constructed solely out of gauge fields. Such operators have been recently proposed as a source of a possibly large neutron electric dipole moment.

Transition form factors have been extracted from inclusive electron scattering data in the ${\mathit{Q}}^2$ range 1 to 10 ${\mathrm{GeV}}^2$/${\mathit{c}}^2$ for the Δ(1232) and second resonance, which is dominated by the ${\mathit{S}}_{11}$(1535). The form factor for the second resonance appears to approach a ${\mathit{Q}}^{\mathrm{-}4}$ dependence expected from leading-order perturbative QCD, while the form factor for the Δ(1232) decreases faster than ${\mathit{Q}}^{\mathrm{-}4}$, which would be expected when nonleading processes are dominant.

We have searched for the annihilation of ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ into the exclusive channels ${\mathit{e}}^{\pm }$${\mathrm{\tau }}^{\mp }$ and ${\mathrm{\mu }}^{\pm }$${\mathrm{\tau }}^{\mp }$ at √s =29 GeV, using 226 and 133 ${\mathrm{pb}}^{\mathrm{-}1}$, respectively, of data taken with the Mark II detector at the SLAC storage ring PEP. The resulting candidate sample is compatible with the expected background from τ pair production. Our analysis yields 95%-C.L. cross-section limits of ${\mathrm{\sigma }}_{\mathit{e}\mathrm{\tau }}$/${\mathrm{\sigma }}_{\mathrm{\mu }\mathrm{\mu }}$<1.8×${10}^{\mathrm{-}3}$ and ${\mathrm{\sigma }}_{\mathrm{\mu }\mathrm{\tau }}$/${\mathrm{\sigma }}_{\mathrm{\mu }\mathrm{\mu }}$<6.1×${10}^{\mathrm{-}3}$, where ${\mathrm{\sigma }}_{\mathrm{\mu }\mathrm{\mu }}$ is the QED cross section for production of a lepton pair. This is the first high-${\mathit{Q}}^2$ test of lepton-flavor conservation involving τ leptons.

Absolute branching fractions for the ${\mathit{D}}_{\mathit{l}3}$ and ${\mathit{D}}_{\mathit{l}4}$ decays ${\mathit{D}}^{+}$→K¯ ${}_{}{}^0{}_{}{}^{}$${\mathit{e}}^{+}$${\nu }_{\mathit{e}}$,${\mathit{D}}^{+}$→K¯ ${}_{}{}^0{}_{}{}^{}\mathrm{\mu }_{}^{+}{}_{}{}^{}$${\nu }_{\mathrm{\mu }}$, ${\mathit{D}}^{+}$→K¯ ${}_{}{}^{\mathrm{*}0}{}_{}{}^{}$${\mathit{e}}^{+}$${\nu }_{\mathit{e}}$, and ${\mathit{D}}^0$→${\mathit{K}}^{\mathrm{*}\mathrm{-}}$${\mathit{e}}^{+}$${\nu }_{\mathit{e}}$ are determined using completely reconstructed DD¯ events at the ψ(3770). Reconstructed ${\mathit{D}}^0$→${\mathit{K}}^{\mathrm{-}}$${\mathit{e}}^{+}$${\nu }_{\mathit{e}}$ decays are used to determine the pole mass of the ${\mathit{f}}_4$(${\mathit{q}}^2$) form factor. Resonant ${\mathit{K}}^{\mathrm{*}}$ production dominates the process D→Kπeν; the ${\mathit{K}}^{\mathrm{*}}$ polarization is measured. Limits on several Cabibbo-suppressed channels are evaluated. A global fit imposing isospin symmetry is performed to the measured exclusive and inclusive semileptonic ${\mathit{D}}^0$ and ${\mathit{D}}^{+}$ branching fractions to obtain an improved set of branching fractions.

The electric polarizability of the neutron was determined to be ${\mathrm{\alpha }}_{\mathit{n}}$=(1.20±0.15±0.20)×${10}^{\mathrm{-}3}$ ${\mathrm{fm}}^3$ from its characteristic influence on the energy dependence of the neutron${\mathrm{-}}^{208}$Pb scattering cross section, as measured in a neutron time-of-flight transmission experiment at the Oak Ridge Electron Linear Accelerator pulsed neutron source.

Quasistatic field configurations are computed for the two-Skyrmion system with large separation. The total energy obtained is much lower than that for the product approximation. In particular, the repulsion in the two-pion range is considerably reduced.

An accurate particle-number-conserving calculation shows that in a single-j (j=13/2) model the yrast-yrare interaction V is always strong and no periodic oscillation of V with Fermi energy λ is obtained. However, in a two-j model or realistic nuclei sharp backcrossings do occur for appropriate single-particle level distribution and oscillation of V with increasing λ is found. The occupation-number distribution for the high-j shell plays a key role in understanding the backcrossing properties.

Measurements are reported of orientation asymmetries in the forward-angle differential cross sections for pion single-charge-exchange scattering of aligned and unaligned ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$ nuclei. The extrapolated 0° asymmetry of -0.022±0.024 indicates a quadrupole deformation ratio ${\mathrm{\beta }}_2^{\mathit{a}}$/${\mathrm{\beta }}_2^{\mathit{c}}$=0.84±0.08. This result conflicts with the predictions of the best available Hartree-Fock models.

Four new superdeformed bands have been observed in ${}_{}{}^{194}{}_{}{}^{}\mathrm{Tl}$, in addition to the two already reported. These six bands consist of three signature-partner pairs, whose energies and spacings closely resemble those in the two superdeformed bands recently reported in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Tl}$. The transition-energy similarities and angular momentum alignments of these bands are discussed.

The concept of resonant tunneling is invoked to explain the sharp drop in the measured spontaneous-fission half-life when going from ${}_{}{}^{256}{}_{}{}^{}\mathrm{Fm}$ to ${}_{}{}^{258}{}_{}{}^{}\mathrm{Fm}$. Various consequences of such a suggestion on the other observed characteristics of the bimodal symmetric fission of ${}_{}{}^{258}{}_{}{}^{}\mathrm{Fm}$ are briefly discussed.

We present an argument based on classical mechanics that stabilization of real atoms in superintense laser fields requires substantially higher frequencies than it is suggested by the analysis of simplified one-dimensional models.

The region of the second dissociation limit of ${\mathrm{H}}_2$ converging to H(1s)+H(2s,2p) has been investigated using high-resolution double-resonance spectroscopy through the E,${\mathit{F}}^1$${\mathrm{\Sigma }}_{\mathit{g}}^{+}$ state. Transitions to the very high vibrational levels of the ${\mathit{B}}^1$${\mathrm{\Sigma }}_{\mathit{u}}^{+}$, B’ ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$, and ${\mathit{C}}^1$${\mathrm{\Pi }}_{\mathit{u}}$ states have been measured with 0.02-${\mathrm{cm}}^{\mathrm{-}1}$ accuracy. Numerous perturbations and unexpected transitions are observed as far as 10 ${\mathrm{cm}}^{\mathrm{-}1}$ below the dissociation limit. This complex structure, still not fully understood, arises from a combination of electronic, fine-structure, and hyperfine interactions.

A general quantum theory of continuous photodetection is applied to an initially squeezed state to clarify effects of quantum-mechanical measurement backaction on a highly nonclassical field. The remaining photon field is found to oscillate in time between super- and sub-Poissonian photon statistics due to the backaction of the photon-number measurement.

It is demonstrated that the nonperturbative coupled-channel method can be efficiently extended to very-high-lying continuum states by using a sufficiently large basis set of Gaussian-type orbitals. In applying the method to the Thomas mechanism in ${\mathrm{H}}^{+}$+H collisions at 5 MeV, we identify two distinct and interfering reaction paths, one via the target and one via the projectile continuum. We get remarkable agreement with experimental data.

A generalized class of Cantor-set models are introduced in a deductive way to explain the intermittent and multifractal structure in the inertial range of isotropic turbulence. All such Cantor-set models are produced by taking the probability density of the stochastic ratio of averaged disspations in the basic breakdown process with scale ratio ${\mathit{A}}^{\mathrm{-}1}$, ${\mathrm{\varepsilon }}_{\mathit{r}}$/${\mathrm{\varepsilon }}_{\mathit{A}\mathit{r}}$, as a polynomial δ function, and it is proved that only some can guarantee the f-α spectra with a non-negative f. The whole statistics of the dissipation density, its square root, and the scaling index α which these models should imply are revealed, and typical models are compared with a recent direct numerical simulation to indicate promising applications.

We present a phase diagram for fluid invasion of porous media as a function of pressure P and the contact angle θ of the invading fluid. Increasing P leads to perculation above a critical ${\mathrm{\theta }}_{\mathit{c}}$, and depinning below ${\mathrm{\theta }}_{\mathit{c}}$. Depinning is characterized by a diverging coherence length and the power-law distribution of events typical of self-organized critical phenomena. At the transition from percolation to depinning another correlation length diverges and an order parameter, an effective macroscopic surface tension, becomes nonzero. The fluid interface changes from self-similar to self-affine. Results are compared to experiments.

The results of specific-heat measurements at the nematic- (N) to-neat-soap (NS) and nematic-to-isotropic (I) phase transitions in binary mixtures of cesium-perfluoro-octanoate and water are reported. The ratio of specific-heat amplitudes above and below the N-NS transition, ${\mathrm{A}}^{+}$/${\mathrm{A}}^{\mathrm{-}}$, and the specific-heat exponent α remain ∼1.0 and ≤0.02, respectively, suggesting 3D XY-type behavior. At the first-order N-I transition, vanishing latent heat and coexistence range at low concentration indicate the existence of a Landau point.

Using infrared-visible sum-frequency generation we have obtained the vibrational spectra of CH stretches of methanol molecules at the interface between methanol vapor and liquid. This is the first vibrational spectrum ever observed from a neat liquid surface. The measured polarization dependence and phase of the nonlinear susceptibility allow us to conclude that the surface methanol molecules are polar oriented with the ${\mathrm{CH}}_3$ group pointing away from the liquid with a very broad orientational distribution.