The strength of the CMB fluctuations on different angular scales as measured by BOOMERANG: points with error bars are the data, while the curve corresponds to the best-fitting cosmological model.

Andrew Lange, California Institute of Technology
John Ruhl, University of California, Santa Barbara
Andrew Jaffe, Center for Particle Astrophysics, University of California, Berkeley
Julian Borrill, NERSC, Lawrence Berkeley National Laboratory

Research Objectives
In January 1999 the BOOMERANG Long Duration Balloon flight spent 10.5 days in the Antarctic stratosphere measuring the temperature of the cosmic microwave background (CMB). The resulting data set is the most significant measurement of the tiny fluctuations in the CMB temperature since they were first detected by the COBE satellite. This research project is devoted to analysis of this data set.

Computational Approach
The analysis of a massive CMB data set can be recast as a problem in the solution of linear systems involving very large, dense, symmetric matrices. First we convert the time-ordered CMB data to a pixelized map, triangular-solving a linear system with a single right hand side to obtain the maximum of the map likelihood function. Then we apply a Newton-Raphson iterative method to locate the peak of the CMB power spectrum likelihood function (which has no closed-form solution) given this map. Each iteration requires triangular-solving many linear systems, each with as many right hand sides as there are pixel-pixel correlation matrix rows and columns. The entire analysis algorithm has been implemented in parallel as the Microwave Anisotropy Dataset Computational Analaysis Package (MADCAP).

Accomplishments
This year saw the first publication of results from the BOOMERANG LDB experiment. Using the MADCAP code on the T3E at NERSC, we analyzed the output of individual detectors and confirmed the high quality of the data. We then produced a map of 30,000 pixels. We excised the highest-quality central region of this map, comprising 8,000 pixels. From this region, we estimated a single gold-plated angular power spectrum over a broad range of angular scales, also with MADCAP. We analyzed this power spectrum and determined such cosmological parameters as the geometry of the Universe and the power spectrum of density perturbations. We have shown that these are consistent with expectations of the inflationary paradigm for the origin of structure in the Universe.

Significance
The CMB is the earliest photon-picture of the Universe we can ever obtain, showing the state of the Universe 300,000 years after the Big Bang. It is our best window onto the early Universe and the most powerful discriminant between competing cosmological models. The tiny fluctuations in the CMB temperature correspond to the very first density perturbations in the Universe. Their pattern contains detailed information about all the fundamental parameters of cosmology — the Universe's geometry, expansion rate, number of neutrino species, ionization history, and the energy density in baryons, dark matter, and cosmological constant.

Publications
A. H. Jaffe et al., "Cosmology from MAXIMA-1, BOOMERANG and COBE/DMR CMB observations," Phys. Rev. Lett. (submitted); astro-ph/0007333 (2000).

A. E. Lange et al., "First estimations of cosmological parameters from BOOMERANG," Phys. Rev. D (submitted); astro-ph/0005004 (2000).

P. de Bernardis et al., "A flat Universe from high-resolution maps of the cosmic microwave background radiation," Nature 404, 955 (2000).

http://www.physics.ucsb.edu/~boomerang/
http://www.nersc.gov/~borrill/cmb/madcap.html
http://www.nersc.gov/news/newsroom/boomerang4-26-00.html