Delensing Cosmic Microwave Background B-modes with the Square Kilometre Array Radio Continuum Survey

We explore the potential use of the Radio Continuum (RC) survey conducted by the Square Kilometre Array (SKA) to remove (delens) the lensing-induced B-mode polarization and thus enhance future cosmic microwave background (CMB) searches for inflationary gravitational waves. Measurements of large-scale B-modes of the CMB are considered to be the best method for probing gravitational waves from the cosmic inflation. Future CMB experiments will, however, suffer from contamination by non-primordial B-modes, one source of which is the lensing B-modes. Delensing, therefore, will be required for further improvement of the detection sensitivity for gravitational waves. Analyzing the use of the two-dimensional map of galaxy distribution provided by the SKA RC survey as a lensing mass tracer, we find that joint delensing using near future CMB experiments and the SKA phase 1 will improve the constraints on the tensor-to-scalar ratio by more than a factor of $\sim 2$ compared to those without the delensing analysis. Compared to the use of CMB data alone, the inclusion of the SKA phase 1 data will increase the significance of the constraints on the tensor-to-scalar ratio by a factor $1.2$-$1.6$. For LiteBIRD combined with a ground-based experiment such as Simons Array and Advanced ACT, the constraint on the tensor-to-scalar ratio when adding SKA phase 2 data is improved by a factor of $2.3$-$2.7$, whereas delensing with CMB data alone improves the constraints by only a factor $1.3$-$1.7$. We conclude that the use of SKA data is a promising method for delensing upcoming CMB experiments such as LiteBIRD.