The detection of primordial gravity waves created during the Big Bang ranks among the greatest potential intellectual achievements in modern science. During the last decades, the instrumental progress has been nothing short of breath taking. However, from the latest ultra-sensitive experiments such as BICEP2 and Planck, it is clear that instrumental sensitivity alone will not be sufficient to make a robust detection of gravitational waves. Contamination in the form of astrophysical radiation from the Milky Way, for instance thermal dust and synchrotron radiation, obscures the cosmological signal by orders of magnitude, and second-order interactions between this radiation and the instrument characterization lead to a highly non-linear problem.
The BeyondPlanck collaboration has implemented a ground-breaking solution to this problem that allows for joint estimation of cosmological parameters, astrophysical components, and instrument characterization. The engine of this method is called Gibbs sampling, and this has now been applied to analysis of raw time-ordered observations observed directly by the instrument, opening up entirely new possibilities for modelling and understanding instrumental systematic effects. As a demonstration of the method, we have analyzed the Planck LFI observations, and delivered a new set of state-of-the-art Planck LFI maps that includes a completely new uncertainty description in the form of Monte Carlo samples. We have also combined these data with similar observations from WMAP (23-94 GHz), and produced the world’s best measurements of polarized synchrotron emission at CMB frequencies. These data products and mehods will play a central role in designing and optimizing future inflationary gravitational wave experiments.
