Primordial gravitational waves and B-mode observations

CMB B-mode is thought to be a crucial signal for the inflationary gravitational waves. Such tensor modes, however, can be generated at the early Universe by other mechanisms than inflation. To distinguish each other, we focus on the information from the B-mode observations to be done with the future missions such as LiteBIRD and CMB-S4. In the first part of my talk, we consider the reconstruction of the primordial tensor power spectrum with LiteBIRD, and quantify how well we can constrain the amplitude of the tensor modes binned in wavenumber. Our study provides an algorithm to distinguish the generation mechanisms in a model-independent way [arXiv:1803.00176, PRD98(2018)123511]. In the second part, we focus on the anisotropies of primordial tensor modes, and estimate their detectability. According to our forecast, we find that the anisotropy parameters up to hexadecapole (g_4) can be observed with CMB-S4 [arXiv:1808.08044, PRD98(2018)083522].