D-brane solitons and boojums in field theory and Bose-Einstein condensates

In certain field theoretical models, composite solitons consisting of a domain wall and vortex lines attached to the wall have been referred to as 'D-brane solitons'. We show that similar composite solitons can be realized in phase-separated two-component Bose-Einstein condensates. We discuss the similarities and differences between topological solitons in the Abelian-Higgs model and those in two-component Bose-Einstein condensates. On the basis of the formulation of gauge theory, we introduce the 'boojum charge' to characterize the D-brane soliton in Bose-Einstein condensates.