The ESA Planck satellite, launched in May 2009, provides an unprecedented high resolution survey of the temperature of the cosmic microwave background (CMB) radiation. COSMOS and HPCS@DiRAC resources were vital for the science exploitation efforts in several key Planck papers. This effort has led to new estimates of cosmological parameters – shown in Figure 1. Planck has also crossed important qualitative thresholds, making gravitational lensing and the study of non-Gaussian statistics truly quantitive subject areas for the first time.
Using the unique capabilities of the COSMOS system, consortium members have used Planck data to undertake the most stringent tests of the inflationary paradigm to date by studying the prediction that primordial fluctuations should have Gaussian statistics (most results are in the ground-breaking Planck Non-Gaussianity paper (dp002.03)). The threepoint correlator (“triangles on the sky”) or bispectrum was evaluated to high precision for the first time (Figure 1); it is a 3D tetrahedral object depending on three triangle multipoles l1, l2, l3. Searches were undertaken for the standard forms of local, equilateral and orthogonal bispectra, described by the ‘nonlinearity’ parameter fNL
These limits, up to four times stronger than WMAP, significantly constrain broad classes of alternative inflationary models. Despite the stringent constraints on scale-invariant models, the Planck bispectrum reconstructions exhibit large non-Gaussian signals (Figure 1), inspiring further investigation of other non-Gaussian models using separable modal methods developed on COSMOS. The two most promising classes of models appear to be those with excited initial states (non-Bunch Davies vacua) and those exhibiting periodic features with apparent high significance. Intensive non-Gaussian analysis of the Planck data is ongoing for a broad range of primordial models, as well as investigating second-order late-time effects such as ISW-lensing.