Research Objectives
To develop the novel computational techniques necessary to extract fundamental cosmological parameters from forthcoming cosmic microwave background (CMB) datasets.
Computational Approach
Central to our task is being able to locate and describe the maximum of the likelihood function of the cosmological parameters given the data -- here an N-pixel map -- generated by any one of the forthcoming CMB observations. At present N is at most a few thousand, but this will increase to tens and hundreds of thousands with the MAXIMA and BOOMERANG balloon flights, and to about a million with the MAP and PLANCK satellite missions. Our present approach scales as N-squared in size and N-cubed in time, so a supercomputer like the T3E is essential to our work. However, even the T3E will be unable to handle the largest datasets; we must therefore develop alternative algorithms either with better scaling properties, or able to successively analyze subsets of the overall dataset.
Accomplishments
Our project received funding in September 1997. In the two months since then we have completed the development of the quadratic estimator formalism for performing a rapid search for the maximum of the likelihood function, and have implemented it on the T3E both in serial and in parallel (using the LAPACK and ScaLAPACK libraries respectively). We are currently working to demonstrate the ability of the parallel code to analyse at least the first generation MAXIMA/BOOMERANG data. To this end we are now developing simulated datasets, comprising the signal from a known underlying theory and a model of the instrument noise and sky foregrounds associated with each experiment.
Significance
The Cosmic Microwave Background provides a picture of the universe as it was a mere 100,000 years after the Big Bang. As the earliest possible photon image available to us, it is our most powerful discriminant between different cosmological models. The unprecedently detailed CMB datasets obtained in the next 10 years will allow us to determine the fundamental cosmological parameters -- in many cases currently known to no better than a factor of 2 -- to the 1% level.
Publications
Bond, J. R., A. H. Jaffe, and L. Knox. 1997. Estimating the power spectrum of the cosmic microwave background. Phys. Rev. D, submitted. http://xxx.lanl.gov/ps/astro-ph/9708203
Smoot, G. 1997. The cosmic microwave background anisotropy experiments. http://xxx.lanl.gov/ps/astro-ph/9705135
URLs
http://cfpa.berkeley.edu/group/cmbanalysis/
Cosmic microwave background fluctuation map.