1,657 research outputs found
Aether Drift and the isotropy of the universe: A measurement of anisotropes in the primordial black-body radiation
Large-angular-scale anisotropies in the 3 K primordial black-body radiation were detected and mapped with a sensitivity of 2 x to the minus 4 power K and an angular resolution of about 10 deg. The motion of the Earth with respect to the distant matter of the Universe ("Aether Drift") was measured and the homogeneity and isotropy of the Universe (the "Cosmological Principle") was probed. The experiment uses two Dicke radiometers, one at 33 GHz to detect the cosmic anisotropy, and one at 54 GHz to detect anisotropies in the residual oxygen above the detectors. The system was installed in the NASA-Ames Earth survey aircraft (U-2), and operated successfully in a series of flights in both the Northern and Southern Hemispheres. Data taking and analysis to measure the anisotropy were successful
Small Angular Scale Simulations of the Microwave Sky
We describe and compare two types of microwave sky simulations which are good
for small angular scales. The first type uses expansions in spherical
harmonics, and the second one is based on plane waves and the Fast Fourier
Transform. The angular power spectrum is extracted from maps corresponding to
both types of simulations, and the resulting spectra are appropriately
compared. In this way, the features and usefulness of Fourier simulations are
pointed out. For , all the simulations lead to similar
accuracies; however, the CPU cost of Fourier simulations is times
smaller than that for spherical harmonic simulations. For , the
simulations based on spherical harmonics seem to be preferable.Comment: 16 pages (LATEX), 2 postcript figures. Accepted in Ap
Low gravity phase separator
An apparatus is described for phase separating a gas-liquid mixture as might exist in a subcritical cryogenic helium vessel for cooling a superconducting magnet at low gravity such as in planetary orbit, permitting conservation of the liquid and extended service life of the superconducting magnet
Constraining Gravitino Dark Matter with the Cosmic Microwave Background
We consider super-gravity models in which the lightest supersymmetric
particle (LSP) is a stable gravitino. The next-to-lightest supersymmetric
particle (NLSP) freezes out with its thermal relic density and then decays
after sec, injecting high-energy photons into the cosmic
plasma. These photons heat up the electron plasma which then thermalizes with
the cosmic microwave background (CMB) via Compton scattering, bremsstrahlung
and double-Compton scattering. Contrary to previous studies which assume
instantaneous energy injection, we solve the full kinetic equation for the
photon number density with a source term describing the decay of the NLSP. This
source term is based on the requirement that the injected energy be almost
instantaneously redistributed by Compton scattering, hence leading to a
time-dependent chemical potential. We investigate the case of a stau NLSP and
determine the constraints on the gravitino and stau masses from observations of
the CMB spectrum by assuming that all gravitino LSPs come from stau NLSP
decays. Unlike the analytical approximations, we find that there may be a stau
mass below which the constraint from the CMB spectrum vanishes.Comment: 8 pages, 6 figures, revtex4, replaced to match published versio
- …