CMB Science in Canada

The previous decade of CMB science has led to incredible new discoveries and key science results including the detection of CMB lensing from temperature and polarization measurements, constraints on light relics and primordial non-Gaussianity and the measurements of Sunyaev-Zel’dovich signals by leveraging the CMB as a backlight to astrophysical objects between us and the last scattering surface. With significant improvements to detector and cryogenic technologies, the coming decade promises to be just as rich scientifically. We discuss fundamental science with CMB fluctuations, including the search for primordial B-modes on large scales to constrain the inflation through the tensor-to-scalar ratio, the dark sector through neutrino mass and light relics with the small-scale CMB power spectrum. We highlight current and planned advances in sensitivity of the CMB facilities and describe international collaborations with significant Canadian participation, including the Atacama Cosmology Telescope, the South Pole Telescope, SPIDER, BICEP-Keck, CGEM, the Simons Observatory, CCAT-p, TAURUS, CMB Stage-4, and LiteBIRD, and the Canadian involvement in the international CMB landscape. In a separate paper, we will highlight the science possible with wide surveys at submm-to-mm wavelengths, including measurements of the Sunyaev-Zel’dovich effect from galaxies, the Cosmic Infrared Background, and cross-correlations with other probes to learn about astrophysics at intermediate redshifts. Our white paper will outline the complementarity of various Canadian CMB efforts on the ground, in balloons and in space. We will address the need for Canadian support of these projects, to leverage the significant expertise in both theoretical and experimental cosmology within Canada. Canadians have been supported through traditional funding mechanisms (NSERC, CFI) for their ground-based efforts. As the community coalesces around LiteBIRD as the major satellite-based observatory for CMB polarization, dedicated mission-level funding is needed from the Canadian Space Agency for Canadians to realize their global leadership—this funding is the most challenging aspect of CMB science for the next decade.