The Cosmic Microwave Background (CMB) carries information from the very first moments of existence of our universe.The picture of its anisotropies which formed some 300,000 years after the Big Bang when radiation and matter decoupled, conveys information about its matter and energy content. 

CMB polarization allows us to go even further back in time, to the very first fraction of a second, in which cosmological inflation is believed to have happened. Cosmological inflation, the leading hypothesis to resolve the problems in the Big Bang theory, predicts that primordial gravitational waves were created during the inflationary era, which then imprinted large-scale curl patterns in the CMB polarization map, called the B-modes. 

The measurement of the very faint B-modes requires the development of specialized detectors and electronics: superconducting bolometers coupled to antennas to be sensitive to the microwaves, read out by SQUIDs, amplifiers based on quantum interference in a superconducting loop, all living at sub-Kelvin temperatures.

Several experiments are under way or being planned in this search, from ground, balloon, or satellite and INFN is presently involved in some. In particular LiteBIRD (the Lite satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection) has been selected as the next JAXA’s strategic large mission, to be launched in the late 2020s with the primary scientific objective to search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will in fact provide also insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. 

I will describe LiteBIRD in some details, highlighting Italian and, in particular, INFN contribution to the mission. 

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