APEC Seminar (Astronomy - Particle Physics - Experimental Physics - Cosmology)

Speaker: Guillaume Patanchon (APC)
Title: Cosmic Microwave Background observations, from Planck to LiteBIRD
Date (JST): Wed, Aug 10, 2022, 14:00 - 15:00
Place: Zoom
Abstract: The Cosmic Microwave Background (CMB) is a radiation from 380000 years after the Big-Bang measured today at the temperature of 2.7 Kelvins. The small fluctuations at the level of 100 microK contain a wealth of information about the primordial Universe. The signal is polarised and two types of polarisation patterns on the sky can be produced: the positive parity E modes sourced by density perturbations and a peculiar negative parity polarisation pattern called B-modes. B-modes are expected to be generated by primordial gravitation waves produced during the hypothetical inflation phase of the Universe happening 10^-34 s after the Big-Bang. It is a unique probe of the early Universe physics.
The Planck satellite provided cosmic variance limited temperature fluctuations over the whole sky and most of the relevant angular scales. This led to percent accuracy measurement of the main cosmological parameters of the standard cosmological model. Planck also provided accurate measurements of E-modes leading to an estimation of the optical depth tau. Planck measurements required understanding many sources of systematic effects coming from the instrument itself, from the satellite environment as well as astrophysical sources, and required intensive data analysis to process them. Polarisation measurement was particularly difficult because it requires differencing measurements taken under different condition on a large intensity background.

LiteBIRD is a satellite mission of JAXA (with the participation of other agencies such as CNES of France) to be launched at the end of 2020’s targeting the B-mode signal at large angular scales by measuring the whole sky in 15 different frequency bands with several thousands of detectors (while Planck was using < 100 detectors). This extremely accurate measurement will require the control systematic effects with unprecedented accuracy. After introducing the CMB physics, I will present the Planck results and analysis. I will then review the possible sources of systematics for LiteBIRD and how to handle them.