Various works have suggested that the Bondi-Sachs-Penrose decay conditions on the gravitational field at null infinity are not generally representative of asymptotically flat spacetimes. We have made a detailed analysis of the constraint equations for ‘‘asymptotically hyperboloidal’’ initial data and find that log terms arise generically in asymptotic expansions. These terms are absent in the corresponding Bondi-Sachs-Penrose expansions, and can be related to explicit geometric quantities. We have nevertheless shown that there exists a large class of ‘‘nongeneric’’ solutions of the constraint equations, the evolution of which leads to spacetimess satisfying the Bondi-Sachs-Penrose smoothness conditions.

We calculate the baryon asymmetry of the Universe which would arise during a first-order electroweak phase transition due to minimal-standard-model processes. It agrees in sign and magnitude with the observed baryonic excess, for reasonable Kobayashi-Maskawa parameters and ${\mathit{m}}_{\mathit{t}}$ in the expected range, and plausible values of bubble velocity and other high temperature effects.

We investigate the evolution of small perturbations around black strings and branes which are low energy solutions of string theory. For simplicity we focus attention on the zero charge case and show that there are unstable modes for a range of time frequency and wavelength in the extra 10-D dimensions. These perturbations can be stabilized if the extra dimensions are compactified to a scale smaller than the minimum wavelength for which instability occurs and thus will not affect large astrophysical black holes in four dimensions. We comment on the implications of this result for the cosmic censorship hypothesis.

Using recent advances in the understanding of noncritical strings, we construct a unique, conformally invariant continuation to off-shell momenta of Polyakov amplitudes in critical string theory. Three-point amplitudes are explicitly calculated. These off-shell amplitudes possess some unusual, apparently stringy, characteristics, which are unlikely to be reproduced in a string field theory. Thus our results may be an indication that some fundamentally new formulation, other than string field theory, will be required to extend our understanding of critical strings beyond the Polyakov path integral.

We show that in minimal SO(10) models where the fermions have Yukawa couplings to only one (complex) 10 and one 126 of Higgs scalars the standard model doublet contained in the 126 receives an induced vacuum expectation value at tree level. In addition to correcting the bad asymptotic mass relations ${\mathit{m}}_{\mathit{d}}$=${\mathit{m}}_{\mathit{e}}$ and ${\mathit{m}}_{\mathit{s}}$=${\mathit{m}}_{\mathrm{\mu }}$, this also leads to a predictive neutrino spectrum. We find that (i) the ${\nu }_{\mathit{e}\mathrm{-}}$${\nu }_{\mathrm{\mu }}$ mixing angle lies in the range sin${\mathrm{\theta }}_{\mathit{e}\mathrm{\mu }}$=0–0.3, (ii) sin${\mathrm{\theta }}_{\mathit{e}\mathrm{\tau }}$≃3‖${\mathit{V}}_{\mathit{t}\mathit{d}}$‖≃0.05, (iii) sin${\mathrm{\theta }}_{\mathrm{\mu }\mathrm{\tau }}$≃3‖${\mathit{V}}_{\mathit{c}\mathit{b}}$‖=0.12–0.16, and (iv) ${\mathit{m}}_{\nu \mathrm{\tau }}$/${\mathit{m}}_{\nu \mathrm{\mu }}$≥${10}^3$, implying that ${\nu }_{\mathrm{\mu }\mathrm{-}}$${\nu }_{\mathrm{\tau }}$ oscillations should be accessible to forthcoming experiments.

We evaluate the infinite-volume, continuum limits of eight hadron mass ratios predicted by lattice QCD with Wilson quarks in the valence (quenched) approximation. Each predicted ratio differs from the corresponding observed value by less than 6%.

We have examined the double-beta decay mode accompanied by Majoron emission. After 223 days of measurement corresponding to about 615 kg d or 19.3 mol yr of exposure we find a lower half-life limit for this decay channel of ${\mathit{T}}_{1/2}^{0\nu \mathrm{\chi }}$>1.66(1.99)×${10}^{22}$ yr [90% (68%) C.L.] yielding a new limit for the Majoron-neutrino coupling of 〈${\mathit{g}}_{\nu \mathrm{\chi }}$〉<1.8×${10}^{\mathrm{-}4}$ (90% C.L.).

I point out that β-delayed proton spectroscopy is a powerful probe of possible scalar contributions to nuclear β decay, and use Schardt and Riisager’s data on the shape of the beta-delayed proton peaks from the superallowed decays of ${}_{}{}^{32}{}_{}{}^{}\mathrm{Ar}$ and ${}_{}{}^{33}{}_{}{}^{}\mathrm{Ar}$ to set improved upper limits on such couplings. Implications of these limits for leptoquark masses are mentioned.

We study dilepton production from a quark-gluon plasma of given energy density at finite quark chemical potential μ and find that the dilepton production rate is a strongly decreasing function of μ. Therefore, the signal to background ratio of dileptons from a plasma created in a heavy-ion collision may decrease significantly.

The total cross section for pion production in the reaction pd→pd${\mathrm{\pi }}^0$ has been measured for bombarding energies from ${\mathit{T}}_{\mathit{p}}$=208.4 MeV to 294.6 MeV. This corresponds to maximum pion momenta η=${\mathit{p}}_{\mathrm{\pi },\mathrm{c}.\mathrm{m}.\mathrm{}}$/${\mathit{m}}_{\mathrm{\pi }}$c between 0.099 and 0.96. The experiment was performed using an electron-cooled proton beam and an internal deuterium gas jet target. The resulting ${\mathrm{\sigma }}_{\mathrm{tot}}$ changes by almost four orders of magnitude over the covered energy range. The results are compared to a model which assumes quasi-free production via the pn→d${\mathrm{\pi }}^0$ elementary process.

The ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(e,e’p${)}^3$H reaction has been measured at a missing momentum of 265 MeV/c. Data were taken to determine the ${\mathit{R}}_{\mathit{L}}$, ${\mathit{R}}_{\mathit{T}}$, and ${\mathit{R}}_{\mathit{L}\mathit{T}}$ response functions. The extracted response functions show substantial differences from a microscopic calculation that includes the plane wave impulse approximation, final state interactions, and meson exchange currents, but agree much better with a calculation that includes orthogonality corrections, short range correlations, and final state interactions.

We have measured the first complete angular correlations of α-particle emission from the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ isoscalar giant quadrupole resonance (${\mathrm{GQ}}_0$R) following excitation by inelastic electron scattering, for momentum transfers from 0.24 to 0.61 ${\mathrm{fm}}^{\mathrm{-}1}$. Analysis of these uniquely determines the ${\mathrm{GQ}}_0$R strength distribution for the ${\mathrm{\alpha }}_0$ channel and sets limits on that for ${\mathrm{\alpha }}_1$.

The high-spin properties of the density dependent Gogny force are analyzed for the first time. The self-consistent cranking Hartree-Fock-Bogoliubov equations have been solved to analyze the rotational nucleus ${}_{}{}^{164}{}_{}{}^{}\mathrm{Er}$. We study pairing properties, moments of inertia, E2 transitions, and gyromagnetic factors, among others, as a function of the angular momentum. The agreement with the available experimental results is very satisfactory.

A photon scattering experiment has been performed on the odd-A nucleus ${}_{}{}^{143}{}_{}{}^{}\mathrm{Nd}$. Strong dipole excitations have been detected in the energy region around 3.2 MeV. This is near the expected position of the two-phonon ($2^{+}$⊗$3^{\mathrm{-}}$) multiplet in the even-even neighboring nucleus ${}_{}{}^{142}{}_{}{}^{}\mathrm{Nd}$. The summed dipole strength between 2.8 and 3.6 MeV in ${}_{}{}^{143}{}_{}{}^{}\mathrm{Nd}$ is in agreement with the sum rule for weak particle coupling to the core nucleus ${}_{}{}^{142}{}_{}{}^{}\mathrm{Nd}$. Model calculations in a harmonic approximation are in a very good agreement with the experiment and they suggest a two-phonon ($2^{+}$⊗$3^{\mathrm{-}}$) particle structure of the excitations in ${}_{}{}^{143}{}_{}{}^{}\mathrm{Nd}$.

The evolution of wave packets is investigated in crossed magnetic and electric fields. We report a direct observation of their propagation along classical trajectories in the time domain. Rydberg states of rubidium are excited with a short laser pulse. We monitor the evolution of the wave packet using a delayed, ionizing probe pulse. When the wave packet approaches the nucleus, the ionization signal is enhanced. The first return to the nucleus is observed and is in agreement with semiclassical predictions. Further evolution of the wave packet is also observed.

The atomic masses of both ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ have been measured with a Penning trap mass spectrometer that utilizes a frequency-shift detector to observe ion cyclotron resonances. Present resolution exceeds 1 part in ${10}^9$ and is limited only by the stability of the magnetic field. The leading systematic shift (at ≲1 part in ${10}^{10}$) is due to the residual quadratic B field dependence. The atomic masses have been combined to yield Δ${\mathit{Mc}}^2$${(}^3$H${\mathrm{-}}^3$He)=18 590.1(1.7) eV. The excellent agreement with recent results from β spectrometers lends strong support for new limits on the neutrino’s rest mass.

We study the motion of advected particles in the Kuramoto-Sivashinsky equation. We give numerical evidence as well as analytical arguments for anomalous diffusion in which the particle displacement Δr satisfies 〈[Δr(t)${]}^2$〉∼${\mathit{t}}^{\mathrm{\eta }}$ where η>1. We show that if the flow is initially seeded with many particles, they will coalesce in time and that a passive scalar density tends to an asymptotic (time dependent) distribution, which, for given initial conditions on the velocity field, is independent of the initial distribution of the passive scalar.

The operation of free-electron lasers can be severely limited by the axial velocity spread of the beam electrons. In this Letter we propose methods for reducing the axial velocity spread in electron beams by redistributing the electron energy via interaction with an axially symmetric, slow, TM waveguide mode. In the first method, the energy redistribution is correlated with the electrons’ betatron amplitude, while in the second method it is correlated with the electrons’ synchrotron amplitude. Reductions by more than a factor of 40 in the rms axial velocity spread have been obtained in simulations.

An in situ x-ray reflectivity study of the dynamic evolution of a growing interface was carried out for gold sputter-deposited onto a polished silicon substrate. X-ray reflectivity data were recorded during growth for thicknesses of the gold film ranging from 50 to 3500 Å. A progressive kinetic roughening of the gold-vacuum interface was observed and the time-dependent interfacial width exhibits a power-law behavior. Aided by scanning-tunneling-microscopy measurements the scaling exponents were determined and compared with theoretical studies.

Reflection high energy electron diffraction data collected in the form of an azimuthal plot are analyzed theoretically for the first time. Experimental results for Si(111) at a glancing angle satisfying a Bragg condition are taken from the literature. Calculations are carried out within a multiple scattering approach. Excellent agreement between experimental and theoretical results is achieved. A simple qualitative explanation of the shape of the azimuthal plot analyzed is also presented.