Astrophysics
Cosmic microwave background (CMB) anisotropies probe the primordial density field at the edge of the observable Universe. There is a limiting precision (``cosmic variance'') with which anisotropies can determine the amplitude of primordial…
We study the large scale power spectrum of gravitational wave perturbations of the microwave background in the context of single-bubble open inflation models. We compute the ratio of tensor to scalar contributions to the CMB anisotropies as…
We study the accretion of cold and hot dark matter onto a cosmic string wake using a high-resolution numerical simulation. We verify previous analytical calculations predicting the radius of bound matter around wakes and inflow velocities…
The one-texture universe, introduced by Davis in 1987, is a homogeneous mapping of a scalar field with an $S^3$ vacuum into a closed universe. It has long been known to mathematicians that such solutions, although static, are unstable. We…
We explore the role of non-Gaussian fluctuations in primordial black hole (PBH) formation and show that the standard Gaussian assumption, used in all PBH formation papers to date, is not justified. Since large spikes in power are usually…
We study the phenomenological constraints on a recently proposed model of open inflation in the context of induced gravity. The main interest of this model is the relatively small number of parameters, which may be constrained by many…
We discuss the appropriate normalization of modes required to generate a homogeneous random field in an open Friedmann-Robertson-Walker universe. We consider scalar random fields and certain tensor random fields that can be obtained by…
Neutrino-nucleus elastic scattering is reduced in dense matter because of correlations between ions. The static structure factor for a plasma of electrons and ions is calculated from Monte Carlo simulations and parameterized with a least…
Interferometric gravitational wave detectors could measure the frequency sweep of a binary inspiral [characterized by its chirp mass] to high accuracy. The observed chirp mass is the intrinsic chirp mass of the binary source multiplied by…
We study the metric perturbations produced during inflation in models with two scalar fields evolving simultaneously. In particular, we emphasize how the large-scale curvature perturbation $\zeta$ on fixed energy density hypersurfaces may…
We study the effect that quantum fluctuations produced during the nucleation of a single-bubble open inflationary universe have on the amplitude of temperature anisotropies in the microwave background. We compute the instanton action for…
We compute the angular power spectrum of temperature anisotropies on the microwave sky in the cosmic texture theory, with standard recombination assumed. The spectrum shows `Doppler' peaks analogous to those in scenarios based on primordial…
There are good reasons to consider models of low-energy supersymmetry with very light photinos and gluinos. In a wide class of models the lightest $R$-odd, color-singlet state containing a gluino, the $\r0$, has a mass in the 1-2 GeV range…
We consider a variant of Hybrid Inflation, where inflation is driven by two interacting scalar fields, one of which has a `Mexican hat' potential and the other a quartic potential. Given the appropriate initial conditions one of the fields…
We report observations obtained with the Keck adaptive optics facility of the nearby (d=9.8 pc) binary Gl~569. The system was known to be composed of a cool primary (dM2) and a very cool secondary (dM8.5) with a separation of 5" (49…
Powerful extended radio galaxies in the 3CR survey are observed out to redshifts of about 2. For redshifts greater than about 0.3, the average lobe-lobe size of the sources decreases monotonically with redshift for all reasonable…
We present a compilation of radio, infrared, optical and hard X-ray (2-10kev) data for a sample of 90 Seyfert 2 galaxies(Sy2s) with spectropolarimetric observations (41 Sy2s with detection of polarized broad lines (PBL) and 49 without PBL).…
One-armed oscillation modes in the circumstellar discs of Be stars may explain the cyclical variations in their emission lines. We show that a three-dimensional effect, involving vertical motion and neglected in previous treatments,…
The low-luminosity active galactic nucleus of M81 has been monitored at centimeter wavelengths since early 1993 as a by-product of radio programs to study the radio emission from Supernova 1993J. The extensive data sets reveal that the…
We investigate the evolution of cooling helium atmosphere white dwarfs using a full evolutionary code, specifically developed for following the effects of element diffusion and gravitational settling on white dwarf cooling. The major…