The uniformly frustrated classical XY model can describe Josephson-junction arrays in a transverse magnetic field. It has been suggested that the energy E(f) and the T=0 critical current ${\mathit{i}}_{\mathit{c}}$(f) in the ground state may be highly discontinuous functions when the frustration parameter f goes through rational and irrational values. We show here that E(f) is a continuous function for a wide class of spin-spin interacting potentials including the cosine for which E(f) will be strictly negative for all f. We discuss the behavior of ${\mathit{i}}_{\mathit{c}}$(f) and we show that ${\mathit{i}}_{\mathit{c}}$(f) has a strictly positive lower bound in the case of piecewise parabolic interacting potential.

It is shown that for the Heisenberg antiferromagnet with nearest-neighbor (nn) and next-nearest-neighbor couplings J and J’, Wilson loops of statistical gauge fields are real by virtue of reflection positivity. This excludes the occurrence of T- and P-violating chiral spin liquid states for most J’. The result also holds in the presence of pair hopping away from half filling.

We have measured photoexcitation dynamics in the picosecond time domain in fully trans and partially isomerized (CH${)}_{\mathit{x}}$ and (CD${)}_{\mathit{x}}$ films with different cis/trans content ratios, using the technique of transient photoinduced resonant Raman scattering. Following the distinctively different decay kinetics of cis and trans resonantly enhanced vibrations, we observed an intersystem crossing of photoexcitations from cis to trans segments which is dominated by a diffusion process in the cis segments, with a time constant between 24 and 215 ps depending on the cis/trans ratio.

In analogy to squeezing of light, noise in a classical oscillator can be squeezed to reduce amplitude uncertainty. While this can be achieved to some extent in a harmonic oscillator parametrically driven at 2${\mathrm{\omega }}_0$, true amplitude squeezing is possible in anharmonic oscillators, either by driving at 2${\mathrm{\omega }}_0$ or allowing amplitude-dependent dephasing. These techniques can reduce the uncertainty in measurements of the frequency of an oscillator; for example, the thermal uncertainty in the relativistic frequency shift in single ion mass spectroscopy can be reduced by more than a factor of 5.

In this paper we present the first experimental verification that the sensitivity of a chaotic system to small perturbations (the ‘‘butterfly effect’’) can be used to rapidly direct orbits from an arbitrary initial state to an arbitrary accessible desired state.

Wave functions of a stadium billiard are determined in a microwave analog experiment. It is shown that Gutzwiller’s semiclassical representation of the Green’s function in terms of classical trajectories can account not only for eigenvalue spectra but also for eigenfunction patterns.

Recently proposed rare decays Z′→${\mathrm{f}}_1$f${\mathrm{¯}}_2$V (with V=W or Z and ${\mathrm{f}}_{1,2}$ ordinary fermions and the forward-backward asymmetry are found to be sensitive diagnostic tests for the gauge coupling ratio ${\mathrm{g}}_{\mathrm{R}}$/${\mathrm{g}}_{\mathrm{L}}$ in left-right symmetric models (${\mathrm{SU}}_{2\mathrm{L}}$×${\mathrm{SU}}_{2\mathrm{R}}$×${\mathrm{U}}_{1\left(\mathrm{B}\mathrm{-}\mathrm{L}\right)}$). At projected luminosities of the CERN Large Hadron Collider and the Superconducting Super Collider, ${\mathrm{g}}_{\mathrm{R}}$/${\mathrm{g}}_{\mathrm{L}}$ can be determined statistically to ∼1% for ${\mathrm{M}}_{\mathrm{Z}\prime }$≃1 TeV. The absence of related decays ${\mathrm{W}}^{\prime \pm }$→${\mathrm{f}}_1$f${\mathrm{¯}}_2$${\mathrm{W}}^{\pm }$ would be a clean signature that W′ couples to right-handed currents. Once ${\mathrm{g}}_{\mathrm{R}}$/${\mathrm{g}}_{\mathrm{L}}$ is determined, the ratio ${\mathrm{M}}_{\mathrm{Z}\prime }$/${\mathrm{M}}_{\mathrm{W}\prime }$ and the decays Z′→${\mathrm{W}}^{+}$${\mathrm{W}}^{\mathrm{-}}$(${\mathrm{W}}^{\prime \pm }$→${\mathrm{W}}^{\pm }$Z) provide probes for the symmetry breaking sector.

We present a SU(2${)}_{\mathit{H}}$ model that can simultaneously accommodate a 17-keV pseudo Dirac neutrino ${\nu }_{\mathrm{\tau }}$ as well as a large transition magnetic moment for nearly massless ${\nu }_{\mathit{e}}$ and ${\nu }_{\mathrm{\mu }}$. While the small Dirac term is generated radiatively, the mass corrections for the light neutrinos remain suppressed even on breaking the Voloshin-type SU(2${)}_{\nu }$ symmetry. The cosmological constraints are met by a rapid decay of the ${\nu }_{\mathrm{\tau }}$ into a ${\nu }_{\mathrm{\mu }}$ and a singlet-doublet Majoron.

Current electroweak precision measurements tend to prefer negative values of the oblique radiative parameters, S and T, relative to their standard-model expectations. This tendency is shown to be consistent with the existence of new colorless fermions in the anomaly-free combination of two doublets (${\mathit{N}}_1$,E${)}_{\mathit{L}}$ and (${\mathit{E}}^{\mathit{c}}$,${\mathit{N}}_2$${)}_{\mathit{L}}$ and one singlet ${\mathit{N}}_{3\mathit{L}}$, which are contained in some supersymmetric or ${\mathit{E}}_6$ extensions of the standard model.

If the electroweak symmetry breaking sector contains colored particles weighing a few hundred GeV, then they will be copiously produced at a hadron supercollider. Colored technipions can rescatter into pairs of gauge bosons. As proposed by Bagger, Dawson, and Valencia, this leads to gauge boson pair rates far larger than in the standard model. In this Letter we reconsider this mechanism, and illustrate it in a model in which the rates can be reliably calculated. The observation of both an enhanced rate of gauge-boson-pair events and colored particles would be a signal that the colored particles were pseudo Goldstone bosons of symmetry breaking.

In the semileptonic decays of a heavy quark to a light quark, present models disagree in an essential fashion concerning the shape of the form factors. Both the heavy quark limit of QCD and dispersion relations suggest that the correct form factors contain two distinct contributions. We discuss these as applied to B→πeν and B→ρeν decays. We also describe the inconsistencies of available phenomenological models and discuss how they must be modified.

We show that the generating functional for hard thermal loops with external gluons in QCD is essentially given by the eikonal for a Chern-Simons gauge theory. This action, determined essentially by gauge-invariance arguments, also gives an efficient way of obtaining the hard thermal loop contributions without the more involved calculation of Feynman diagrams.

We present a calculation of antiproton yields in Si+Al and Si+Au collisions at 14.5A GeV in the framework of the relativistic quantum molecular dynamics approach (RQMD). Multistep processes lead to the formation of high-mass flux tubes. Their decay dominates the initial antibaryon yield. However, the subsequent annihilation in the surrounding baryon-rich matter suppresses the antiproton yield considerably: Two-thirds of all antibaryons are annihilated even for the light Si+Al system. Comparisons with preliminary data of the E802 experiment support this analysis.

A new microscopic simulation method of heavy-ion collisions is formulated by incorporating the two-nucleon collision process into the antisymmetrized version of molecular dynamics. This method can describe quantum-mechanical features such as shell effects. The fragment mass distribution of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{12}$C reaction at 28.7 MeV/nucleon is shown to be reproduced very well by this new method combined with the treatment of statistical cascade decays of excited fragments, which verifies the usefulness of the new method.

We report measurements of asymmetries in quasielastic scattering of polarized electrons from polarized ${\mathrm{He}}^3$ at ${\mathrm{Q}}^2$=-0.2 GeV/c${)}^2$. We measure ${\mathrm{A}}_{\mathrm{T}\prime }$=(-2.6±0.9±0.46)% and ${\mathrm{A}}_{\mathrm{TL}\prime }$=(+1.75±1.2±0.31)%. The asymmetry ${\mathrm{A}}_{\mathrm{T}\prime }$ depends predominantly on the previously measured neutron magnetic form factor and provides a test of theories of spin-dependent quasielastic scattering. Our result for ${\mathrm{A}}_{\mathrm{T}\prime }$ is consistent with a previously reported measurement and suggests that the current theoretical picture is incomplete and final-state-interaction and meson-exchange corrections are necessary if the electric form factor of the neutron is to be reliably extracted from the asymmetry of ${\mathrm{A}}_{\mathrm{TL}\prime }$.

The strong-field behavior of a three-body quantum system analogous to a negative ion has been investigated by solving Schrödinger’s equation nonperturbatively for two electrons on a two-dimensional lattice. Both photodetachment and core ionization have been studied, and we find that photospectral time dependence distinguishes between direct and stepwise ionization routes for the inner electron.

We predict the presence of a new, equally spaced sequence of peaks in the above-threshold detachment (ATD) spectra in a very intense laser of a fixed frequency. Using a general theoretical argument, originally made by Wigner in the context of nuclear reaction theory, we identify the new comblike peak sequence as due to Wigner cusps at the thresholds of stimulated multiphoton bremsstrahlung channels in the intermediate continuum states. Our prediction is supported by solving the Schrödinger equation of a 3D model of ${\mathrm{H}}^{\mathrm{-}}$ in an intense infrared laser (ħω=0.35 eV). A way of experimentally distinguishing the new sequence from the usual ATD peaks is pointed out.

We report the first direct observation of a resonancelike structure for positron scattering by an atom or molecule. Our initial absolute elastic differential cross-section measurements for positron scattering by argon when plotted versus energy (8.7 to 300 eV) at fixed scattering angles of 60°, 90°, and 120° reveal an unexpected drop (a factor of 2 at 60°) between 55 and 60 eV. This structure is puzzling because it does not occur near any known inelastic threshold energy and may relate to a cross-channel coupling effect with an open inelastic-scattering channel.

Amplification of spontaneous emission (ASE) at 23.6 nm has been studied in a Ge plasma heated by a 1 TW infrared laser pulse. The exponent of the axial gain reached 21 in a geometry with Fresnel number ≤1. Two plasma columns of combined length up to 36 mm were used with an extreme ultraviolet mirror giving double-pass amplification. Saturation of the ASE output was observed. The beam divergence was about 8× diffraction limited with a brightness estimated at ${10}^{14}$ W ${\mathrm{cm}}^{\mathrm{-}2}$ ${\mathrm{sr}}^{\mathrm{-}1}$. The feedback from the mirror was significantly reduced probably by radiation damage from the plasma.

We present and test a method for simulating the dynamics of turbulence using a strongly reduced subset of Fourier modes with vector triadic interactions. The method allows a resolution of (10 000${)}^2$ in two dimensions and (3000${)}^3$ in three dimensions on present-day computers.