CMB-INFLATE · Advanced Methodologies for Next Generation Large Scale CMB Polarization Analysis

Advanced Methodologies for Next Generation Large Scale CMB Polarization Analysis

Around 10^-37 seconds after the Big-Bang, the Universe went through a rapid expansion phase called inflation with extreme density and temperature conditions such that the known laws of physics do not apply and require a unified theory of quantum gravity. The best probe of this period is a relic emission called Cosmic Microwave Background (CMB) from 380000 years after the big-bang, when the Universe state changed from a hot and opaque plasma to a transparent phase. This emission shows small fluctuations which are the seeds of structures we observe today, and inflation provides a mechanism for the generation of those perturbations: they are quantum fluctuations brought to cosmic scales. This process generates density perturbations measured with high precision experiments, in particular the Planck satellite of ESA. It also produces a background of gravitational waves. The CMB emission is polarized and primordial gravitational waves produce a parity-odd CMB polarization pattern on the sky called B-modes, as illustrated by Figure 1, undetected as of today. The positive parity patterns called E-modes are generated by both types of perturbations. Full sky polarization B-modes varying at roughly 20-degree scales on the sky contains precious information about the inflation physics and can uniquely be probed with future satellite mission such as LiteBIRD of the Japanese space agency JAXA. This is a challenging measurement because of the presence of polarized foreground emissions at frequencies of the CMB emission: polarized thermal Galactic dust and synchrotron emissions. Our capacity to subtract those foreground emissions is one of the current limitations hampering the accurate measurement of large angular scales. Improved modelling of foreground emission, as well as the development of analysis methods incorporating all the complexity of the sky and the instrument are crucial steps for an accurate determination of the primordial signal from inflation with future experiments. Another difficulty is the understanding and mitigation of instrumental effects in data. The success of future experiments will require accurate modelling of those effects in close link with instrumental developments that are now performed over the world. It will also require the development of new innovative analysis techniques to estimate the tiny gravitational wave signal. Analysis techniques will require mathematical developments to reduce efficiently a large volume of data. The main objective of CMB-Inflate is to improve communications and foster collaborations within a community of researchers for advanced and innovative analysis of CMB polarization data focused on the large angular scales (10 degrees and more) with the ultimate goal of measuring in a robust way the tensor modes and the fundamental parameters that describe them to distinguish between the different scenarios of inflation. The network is gathering scientists with diverse expertise and backgrounds from instrumentalists to theoreticians in order to reach the next steps in CMB polarization data analysis consisting in providing a complete and advanced modelling of the data including instrumental effects and all the complexity of the sky emission; and in the development of global analysis of the data, from the raw time-streams to the sky component separation and likelihood analysis for the extraction of science. Moreover, the training of the young community of researchers are an important objective of the CMB-Inflate project.

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