LiteBIRD (Lite (Light) satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection) is a planned small space observatory that aims to detect the footprint of the primordial gravitational wave on the cosmic microwave background (CMB) in a form of polarization pattern called B-mode.
LiteBIRD and OKEANOS were the two finalists for Japan's second Large-Class Mission.[5][6] In May 2019, LiteBIRD was selected by the Japanese space agency.[7]LiteBIRD is planned to be launched in the 2020s with an H3 launch vehicle for three years of observations at a Sun-Earth Lagrangian point L2.[5]
Overview
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.[8] The primordial gravitational waves are expected to be imprinted in the CMB polarization map as special patterns, called the B-mode.[8] Measurements of polarization of the CMB radiation are considered as the best probe to detect the primordial gravitational waves,[9] 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.[8]
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][10] The design concept is being studied by an international team of scientists from Japan, U.S., Canada and Europe.[5][11]
Telescopes
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][12] The baseline design considers an array of 2,622 superconducting polarimetric detectors.[3][12] The entire optical system will be cooled down to approximately 5 K (−268.15 °C; −450.67 °F) to minimize the thermal emission,[13] and the focal plane is cooled to 100 mK with a two-stage sub-Kelvin cooler.[3]
^Mission design of LiteBIRD. T. Matsumura, Y Akiba, J. Borrill, etal. arXive repository. Filed: 12 November 2013.
^ abcdeConcept design of the LiteBIRD satellite for CMB B-mode polarization. Y. Sekimoto; P. Ade; K. Arnold; J. Aumont; J. Austermann, etal. Proceedings Volume 10698, Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave; 106981Y (2018) doi:10.1117/12.2313432 Event: SPIE Astronomical Telescopes + Instrumentation, 9 August 2018, Austin, Texas, United States.
^LiteBIRD: Mission Overview and Focal Plane Layout. T. Matsumura, Y. Akiba, K. Arnold, J. Borrill, R. Chendra, etal. Journal of Low Temperature Physics. August 2016, Volume 184, Issue 3–4, pp 824–831.
^LiteBIRD: mission overview and design tradeoffs. T. Matsumura; Y. Akiba; J. Borrill; Y. Chinone, etal. Proceedings Volume 9143, Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave; 91431F (2014) doi:10.1117/12.2055794 Event: SPIE Astronomical Telescopes + Instrumentation, 2 August 2014, Montréal, Quebec, Canada.
