Recent developments of transition-edge sensors (TESs), based on extensive experience in ground-based experiments, have been making the sensor techniques mature enough for their application on future satellite cosmic microwave background (CMB) polarization experiments. LiteBIRD is in the most advanced phase among such future satellites, targeting its launch in Japanese Fiscal Year 2027 (2027FY) with JAXA's H3 rocket. It will accommodate more than 4000 TESs in focal planes of reflective low-frequency and refractive medium-and-high-frequency telescopes in order to detect a signature imprinted on the CMB by the primordial gravitational waves predicted in cosmic inflation. The total wide frequency coverage between 34 and 448 GHz enables us to extract such weak spiral polarization patterns through the precise subtraction of our Galaxy's foreground emission by using spectral differences among CMB and foreground signals. Telescopes are cooled down to 5 K for suppressing thermal noise and contain polarization modulators with transmissive half-wave plates at individual apertures for separating sky polarization signals from artificial polarization and for mitigating from instrumental 1/f noise. Passive cooling by using V-grooves supports active cooling with mechanical coolers as well as adiabatic demagnetization refrigerators. Sky observations from the second Sun-Earth Lagrangian point, L2, are planned for 3 years.

We revisit the old (fourth-order or quadratically generated) gravity model of Starobinsky in four space-time dimensions, and derive the (inflaton) scalar potential in the equivalent scalar-tensor gravity model. The inflaton scalar potential is used to compute the (CMB) observables of inflation, associated with curvature perturbations (namely, the scalar and tensor spectral indices, and the tensor-to-scalar ratio), including the new next-to-leading-order terms with respect to the inverse number of e-foldings. The results are compared to the recent (WMAP5) experimental bounds. We confirm both mathematical and physical equivalence between f (R) gravity theories and the corresponding scalar-tensor gravity theories.

LiteBIRD is a candidate for JAXA s strategic large mission to observe the cosmic microwave background (CMB) polarization over the full sky at large angular scales. It 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). The concept design has been studied by researchers from Japan, U.S., Canada and Europe during the ISAS Phase-A1. Large scale measurements of the CMB B-mode polarization are known as the best probe to detect primordial gravitational waves. The goal of LiteBIRD is to measure the tensor-to-scalar ratio (r) with precision of δr < 0.001. A 3-year full sky survey will be carried out with a low frequency (34-161 GHz) telescope (LFT) and a high frequency (89-448 GHz) telescope (HFT), which achieve a sensitivity of 2.5 µK-arcmin with an angular resolution of ∼ 30 arcminutes around 100 GHz. The concept design of LiteBIRD system, payload module (PLM), cryo-structure, LFT and verification plan is described in this paper.

We investigate in detail the structure of the simplest non-trivial F (R)-supergravity model, whose F -function is given by a generic quadratic polynomial in terms of the scalar supercurvature R. This toy-model admits a fully explicit derivation of the corresponding f (R)-gravity functions. We apply the stability requirements for selecting the physical f (R)-gravity functions, and discuss the phenomenological prospects of F (R)-supergravity in its application to cosmology.

We reconsider a toy model of topological inflation, based on the R4-modified gravity. By using its equivalence to a certain scalar–tensor gravity model in four spacetime dimensions, we compute the inflaton scalar potential and investigate the possibility of inflation. We confirm the existence of slow-roll inflation with an exit. However, the model suffers from the η-problem that gives rise to the unacceptable value of the spectral index ns of scalar perturbations.