One commonly accepted idea for the origin of the large-scale structure in the Universe is that the minute quantum fluctuations were stretched to macroscopic scales as a consequence of nearly exponential expansion of spacetime during the “cosmic inflation”. Cosmic inflation predicts primordial density fluctuations that are consistent with the observed CMB temperature fluctuations. It also predicts the primordial gravitational waves that imprints on the CMB anisotropy in polarization. LiteBIRD, (the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection), is JAXA’s strategic L-class satellite mission aiming to search for the evidence of cosmic inflation from the CMB polarization signal. I will briefly review the concept, design, and main systematic effects for LiteBIRD, and discuss the challenges of applying the transition-edge sensor and multiplexed readout in space mission. I will also discuss the potential application of TES in X-ray astronomy. Besides the triumph of the concordance Lambda CDM cosmological model that fits with CMB temperature anisotropy at z~1300 and other evidence at low redshift Universe, one intriguing fact is that the baryonic content so far observed in the local Universe can only account for about half of the value predicted by Lambda CDM cosmology. I will show that a novel method — spatial fluctuation analysis of the X-ray background — can shed light on the missing baryon problem. Furthermore, I will discuss other X-ray background related science topics that are beyond the Lambda CDM model and how TES application paves the way to advance this field.
