LiteBIRD

Cosmological inflation is the leading theory of the first instant of the universe, called the Big Bang theory. Inflation postulates that the universe underwent a period of rapid expansion an instant after its formation, and it provides a convincing explanation for cosmological observations.^[3] Inflation predicts that primordial gravitational waves were created during the inflationary era, about 10⁻³⁸ second after the beginning of the universe.^[9] The primordial gravitational waves are expected to be imprinted in the CMB polarization map as special patterns, called the B-mode.^[9] Measurements of polarization of the CMB radiation are considered as the best probe to detect the primordial gravitational waves,^[10] that could bring a profound knowledge on how the Universe began, and may open a new era of testing theoretical predictions of quantum gravity, including those by the superstring theory.^[9]

The science goal of LiteBIRD is to measure the CMB polarization over the entire sky with the sensitivity of δr <0.001, which allows testing the major single-field slow-roll inflation models experimentally.^[1][11] The design concept is being studied by an international team of scientists from Japan, U.S., Canada and Europe.^[5][12]

In order to separate CMB from the galactic emission, the measurements will cover 40 GHz to 400 GHz during a 3-year full sky survey using two telescopes on LiteBIRD.^[3][5] The Low Frequency Telescope (LFT) covers 40 GHz to 235 GHz, and the High Frequency Telescope (HFT) covers 280 GHz to 400 GHz. LFT has a 400 mm aperture Crossed-Dragone telescope, and HFT has a 200 mm aperture on-axis refractor with two silicon lenses.^[3][5][13] The baseline design considers an array of 2,622 superconducting polarimetric detectors.^[3][13] The entire optical system will be cooled down to approximately 5 K (−268.15 °C; −450.67 °F) to minimize the thermal emission,^[14] and the focal plane is cooled to 100 mK with a two-stage sub-Kelvin cooler.^[3]

• POLARBEAR
• BICEP and Keck Array