problems in cosmology. CMB anisotropies sourced by early-universe density perturbations
are currently the most powerful observational probe of the earliest mechanisms of structure
formation. It is possible that the same processes that produced the density perturbations also
sourced tensor perturbations, or primordial gravitational waves (PGWs). If this is the case,
detecting a PGW signal would yield insight into physics far earlier than the epoch of …