A new application of finite size scaling to Monte Carlo simulations is introduced. Using this technique, critical behavior can be investigated at temperatures arbitrarily close to the critical point without large lattice sizes. Applying this method to the two-dimensional standard O(3) model it is shown that for the correlation length asymptotic scaling holds for β≥2.25; the magnetic susceptibility converges to the asymptotic scaling very slowly. In the scaling region, it is observed that the specific heat decreases with β, which implies no singular behavior of the specific heat for this model.

We present a method for the numerical computation of the stress-energy tensor of a quantized scalar field in a general static spherically symmetric spacetime, with or without horizon. The scalar field may have arbitrary curvature coupling and mass. Our method leads in a natural way to a new analytic approximation to the stress-energy tensor for massless scalar fields in these spacetimes. We use the results to compute stress-energy tensors of quantized scalar fields in Schwarzschild and Reissner-Norstro/m black hole spacetimes.

We investigate, using a 1/N expansion, the behavior of a parameter in the scalar-fermion sector of the standard model that shows perturbative nondecoupling as the fermion becomes heavy. This low-energy parameter is related to the S parameter defined through ${\mathit{W}}_3$-B mixing. We obtain the leading 1/N contribution to this parameter that, if expanded perturbatively, collapses to its constant one-loop result. Nonperturbatively, we find that as the mass of the fermion approaches the triviality scale the behavior of the parameter is nonuniversal and shows nondecoupling.

The process AB→quarkonium +γ+X, for heavy quarkonium state such as J/ψ or Υ, is considered. The ratio of the cross sections for this process in pp and pp¯ collisions is shown to be a very sensitive probe of models of quarkonium formation.

We show that quark-antiquark annihilation processes in single-spin inclusive production experiments can yield useful information on hadron spin structure in general, and provide crucial tests for the existence of orbiting valence quarks in particular. There are several experimental indications and theoretical arguments for the existence of such orbital motion inside polarized protons or antiprotons. Simple relations between quark-spin distributions and left-right asymmetries in such production processes can be given, and quantitative predictions can be made.

A precise measurement of the ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$ lifetime using approximately 1340 fully reconstructed ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$→${\mathit{pK}}^{\mathrm{-}}$${\mathrm{\pi }}^{+}$ and charge conjugate decays is presented. The data were accumulated by the Fermilab high energy photoproduction experiment E687. The lifetime of the ${\mathrm{\Lambda }}_{\mathit{c}}^{+}$ is measured to be 0.215±0.016±0.008 ps.

Using a chemically purified sample of ${}_{}{}^{55}{}_{}{}^{}\mathrm{Fe}$ and a coaxial Ge detector, we collected a high-statistics internal-bremsstrahlung photon spectrum, and conducted a local search for departures from a smooth shape near the end point. We find no evidence for emission of a neutrino in the mass range 5–25 keV. In particular, a 17 keV neutrino with ${\sin }^2$θ=0.008 is excluded at the 7σ level.

We have measured antiproton production cross sections as functions of centrality in collisions of 14.6 GeV/c per nucleon ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ ions with targets of Al, Cu, and Pb. For all targets, the antiproton yields increase linearly with the number of projectile nucleons that have interacted, and show little target dependence. We discuss the implications of this result on the production and absorption of antiprotons within the nuclear medium.

The nuclear response of a medium-mass nucleus ${(}^{136}$Xe) to electromagnetic excitation in a near-relativistic heavy-ion collision was investigated in the ${\mathrm{reaction}}^{136}$Xe(0.7A GeV)+Pb. From an exclusive measurement of the neutron decay of the excited ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$ projectiles, strong excitations of giant resonances and, in particular, of the double isovector giant dipole resonance were identified. A resonance energy of 28.3±0.7 MeV, a width of 6.3±1.6 MeV, and a total cross section of 215±50 mb were found for the double giant dipole resonance.

We demonstate a laser-cooled Cs fountain which can be used as a frequency standard. The fountain has been used to measure the frequency shift due to ultracold Cs-Cs collisions at temperatures below 2.8 μK. The measured shift is -12.9±0.7 mHz for a density of (2.7±1.5)×${10}^9$ ${\mathrm{cm}}^{\mathrm{-}3}$ beginning with an even distribution (±10%) among the F=3, ${\mathit{m}}_{\mathit{F}}$ states. For a fountain with 95% of the atoms in the ${\mathit{m}}_{\mathit{F}}$=0 states, we measure a frequency shift of -5.5±0.5 mHz at a density of (3.5±2.0)×${10}^8$ ${\mathrm{cm}}^{\mathrm{-}3}$.

Hydration of sodium in water clusters, Na(${\mathrm{H}}_2$O${)}_{\mathit{n}}$, 1≤n≤8, is investigated using nonlocal pseudopotentials and local-spin-density functional theory, with exchange-correlation gradient corrections. Addition of water molecules to an Na atom results in a successive decrease in the ionization potential, with a marked reduced variation for n>4. This reflects the formation of a molecular shell about the Na for n∼4, accompanied by expulsion of the metal valence electron from the hydration cavity and its delocalization in a ‘‘surface Rydberg-like state.’’

We report photoelectron spectra of sodium chloride cluster anions, (NaCl${)}_{\mathit{n}}$${\mathrm{Na}}^{\mathrm{-}}$(n=1–21), which contain two excess electrons. We observe three distinct types of spectra, corresponding to three different modes for accommodating the two electrons. Our evidence suggests that, in some clusters, the electrons form spin pairs that either occupy a single anion vacancy as an F’ color center or localize on a ${\mathrm{Na}}^{+}$ cation to form a ${\mathrm{Na}}^{\mathrm{-}}$ anion. In other clusters, the two electrons separately occupy a pair of anion vacancies as a double F color center.

We extend the basic idea of inversionless amplification to a picosecond test pulse in the absence of initial optical coherences. The crucial role of population trapping by lower level Zeeman coherence in atomc samarium vapor (J=1⇆J’=0) is demonstrated experimentally and theoretically in a time separated preparation-test setup.

The destruction of quantum localization of chaos by weak nonlinearity is analyzed on the basis of the Chirikov criterion of overlapping resonances. It is shown that for the nonlinear coupling constant there is a delocalization border above which localization is destroyed. In this delocalized phase, excitation is described by a universal anomalous subdiffusion law. Applications of this phenomenon to nonlinear wave propagation in disordered media and Anderson localization are discussed.

We present the results of an experimental study of a supercritical parity-breaking transition in the printer’s instability. Above the transition, the reflection symmetry of a one-dimensional pattern of stationary fingers is broken and the pattern propagates at constant speed. We find the speed of the broken-parity pattern to be proportional to the degree of a symmetry of the pattern, and the wave number to decrease linearly with the asymmetry.

It is demonstrated theoretically that the critical Rayleigh number for transition from the no-motion (conduction) to the motion state in the Rayleigh-Bénard problem of an infinite fluid layer heated from below and cooled from above can be significantly increased through the use of feedback control strategies effecting small perturbations in the boundary data.

A general formula is presented for the mode conversion coefficient for linear mode conversion in one dimension, in terms of an arbitrary 2×2 reduced dispersion matrix describing the coupling of the modes. The mode conversion coefficient has three invariance properties which are discussed, namely, invariance under scaling transformations, canonical transformations, and a certain kind of Lorentz transformation. Formulas for the S matrix of mode conversion are also presented. The example of the conversion of electromagnetic waves to electrostatic waves in the ionosphere is used to illustrate the formulas.

An important conclusion of earlier work using the ballooning representation is that shear damping of plasma drift waves may be suppressed in a torus. This application of the formalism requires that the diamagnetic frequency have a maximum and implies that drift modes can exist only at this maximum. Here we show that there is a far more general class of toroidal drift modes. Shear damping is less well suppressed in these new modes, but they extend over a much larger fraction of the plasma radius. They may therefore have significant implications for plasma transport.

We investigate the shock induced Richtmyer-Meshkov instability at high compression using the Nova laser. The instability and shock characteristics are measured radiographically in planar two-fluid targets with Atwood number <0. The growth of imposed interfacial perturbations η=${\mathrm{\eta }}_0$ sinkx agrees with linear theory if the pre- and postshock initial amplitudes are averaged. When kη∼2, the fundamental mode saturates and harmonics emerge producing a slowly developing bubble and spike.

Numerical analysis of the system of Zakharov and electromagnetic wave equations shows that in the nonlinear stage of saturation of stimulated Raman backscattering a wide spectrum of plasma fluctuations is excited. These fluctuations manifest themselves in enhanced levels of Brillouin and forward Raman scattering. The coupling between stimulated Raman scattering and these secondary scattering processes is theoretically described. We derive new scaling laws for enhanced Brillouin and forward Raman scattering, which can be tested in the current laser-plasma interaction experiments.