After two years of the project, work has been carried out on many fronts. Regarding our first objective, the modeling of instrument components, we have developed a general and innovative model of a half wave plate (HWP), a key optical device to measure the CMB polarization and envisaged by the future satellite mission LiteBIRD. The model, available on a repository, predicts the signal produced by HWP imperfections for different incidence angle and observation frequencies. It is based on calculations of electromagnetic wave propagation through a multi-layer sapphire and anti-reflection coating on the surface.
Moreover, we developed optical model for a satellite mission to accurately account for features producing artefacts in data such as the co- and cross-polarization components of the optical response (called beam) in presence of an HWP. The prediction of the coupling of the optical response with a moving component, the HWP, is the originality of the project.
We also addressed the problem of modelling transition edge sensor (TES) responses using as a baseline the LiteBIRD satellite configuration and we have started a study of the coupling with other components such as the focal plane and the HWP. Emphases have been put on the modeling of non-linear response and the coupling with the HWP signal.
Regarding the second objective: the development of innovative data analysis methods, we have developed new and efficient map-making methods handling systematics, in particular HWP, beam and gain systematics, using models of the instrument components developed within the project. Map-making is an important data analysis step for the CMB measurement, reducing the data from measurements acquired continuously in time by each individual detector to the pixelized maps of the estimated sky signal, also removing instrument effects. One aspect of the work concerned the generalization of the map-making method for the inclusion of other maps than the sky temperature and polarization capturing specific systematics effects: band-pass mismatches, pointing errors, gain errors and HWP spurious systematics. Other methods developed include: joint estimation of maps and instrument parameters (HWP in particular) in a maximum likelihood approach and a Wiener filtering approach.
We have developed astrophysical component separation methods adapted for CMB B-mode searches in light of the most recent foreground emission modeling. Hybrid (or semi-blind) methods are under development and more flexible blind method have been tested in presence of instrumental effects modeled in the project. The inclusion of such effects is the originality of CMB-Inflate. Consequent work has taken place for the comparison of methodologies.
Two simulations frameworks including instrumental and foreground emission models developed in the project were put in place with the objectives of testing our models and methodologies. Instrumental effects that are being integrated in the simulation frameworks include: optical effect convolution; HWP Mueller matrix; noise models and detector response including the interaction with the focal plane.
The last aspect concerns the global end-to-end analysis. Work is performed in synergy with the Cosmoglobe and BeyondPlanck EU funded projects: an analysis pipeline for LiteBIRD is put in place; young researchers participating to the project have been trained for high-level end-to-end data analysis during several secondments; advanced likelihood techniques to estimate science parameters have been developed and tested with our data model.
