42 research outputs found
Cosmic strings, loops, and linear growth of matter perturbations
We describe the detailed study and results of high-resolution numerical
simulations of string-induced structure formation in open universes and those
with a non-zero cosmological constant. The effect from small loops generated
from the string network has also been investigated. We provide a
semi-analytical model which can reproduce these simulation results. A detailed
study of cosmic string network properties regarding structure formation is also
given, including the correlation time, the topological analysis of the source
spectrum, the correlation between long strings and loops, and the evolution of
long-string and loop energy densities. For models with 8 h^{-1}\sigma_8$, and an overall shape which are consistent within
uncertainties with those currently inferred from galaxy surveys. The cosmic
string scenario with hot dark matter requires a strongly scale-dependent bias
in order to agree with observations.Comment: 60 pages, 24 figure
AMiBA Wideband Analog Correlator
A wideband analog correlator has been constructed for the Yuan-Tseh Lee Array
for Microwave Background Anisotropy. Lag correlators using analog multipliers
provide large bandwidth and moderate frequency resolution. Broadband IF
distribution, backend signal processing and control are described. Operating
conditions for optimum sensitivity and linearity are discussed. From
observations, a large effective bandwidth of around 10 GHz has been shown to
provide sufficient sensitivity for detecting cosmic microwave background
variations.Comment: 28 pages, 23 figures, ApJ in press
Recent results from the MAXIMA experiment
MAXIMA is a balloon-borne platform for measuring the anisotropy of the Cosmic
Microwave Background (CMB). It has measured the CMB power spectrum with a
ten-arcminute FWHM beam, corresponding to a detection of the power spectrum out
to spherical harmonic multipole l~1000. The spectrum is consistent with a flat
Universe with a nearly scale-invariant initial spectrum of adiabatic density
fluctuations. Moreover, the MAXIMA data are free from any notable non-Gaussian
contamination and from foreground dust emission. In the same region, the WMAP
experiment observes the same structure as that observed by MAXIMA, as evinced
by analysis of both maps and power spectra. The next step in the evolution of
the MAXIMA program is MAXIPOL, which will observe the polarization of the CMB
with comparable resolution and high sensitivity over a small patch of the sky.Comment: To appear in New Astronomy Reviews, Proceedings of the CMBNET
Meeting, 20-21 February, 2003, Oxford, U
Making Maps Of The Cosmic Microwave Background: The MAXIMA Example
This work describes Cosmic Microwave Background (CMB) data analysis
algorithms and their implementations, developed to produce a pixelized map of
the sky and a corresponding pixel-pixel noise correlation matrix from time
ordered data for a CMB mapping experiment. We discuss in turn algorithms for
estimating noise properties from the time ordered data, techniques for
manipulating the time ordered data, and a number of variants of the maximum
likelihood map-making procedure. We pay particular attention to issues
pertinent to real CMB data, and present ways of incorporating them within the
framework of maximum likelihood map-making. Making a map of the sky is shown to
be not only an intermediate step rendering an image of the sky, but also an
important diagnostic stage, when tests for and/or removal of systematic effects
can efficiently be performed. The case under study is the MAXIMA data set.
However, the methods discussed are expected to be applicable to the analysis of
other current and forthcoming CMB experiments.Comment: Replaced to match the published version, only minor change