Giovanni Signorelli (INFN Pisa)
The Cosmic Microwave Background (CMB) carries information from the very first moments of existence of our universe.The picture of its anisotropies which formed at about 300000 years after the Big Bang when radiation and matter decoupled, conveys information about its matter and energy content. CMB polarization, on the other hand, allows us to go back 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 cosmic microwave background (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, as LSPE, in which INFN is involved, and LiteBIRD, that has just been selected as the next JAXA’s strategic large mission, to be launched in the late 2020s to map the polarization of the CMB radiation over the full sky at large angular scales with unprecedented precision. Precise polarization maps of LiteBIRD will also provide us with valuable pieces of information on particle physics and astrophysics.