Comments on domain walls in holographic duals of mass deformed conformal field theories

We consider M-theory backgrounds which are gravity duals of mass deformed superconformal field theories in 2+1 dimensions. The specific examples we consider are the B_8, Stenzel, and the Lin-Lunin-Maldacena geometries. These geometries contain compact 4-cycles on which one can wrap an M5-brane to create an object which behaves effectively like a domain wall in 2+1 dimensions. We review the quantization of flux and charges of these M-theory backgrounds, and confirm that the back reaction of the domain wall shifts the charges in a manner consistent with these quantization conditions, paying particular attention to various subtle half integer shifts of the charge lattice which arise as a part of the complete story. We also describe a configuration of a stationary, merging M2/anti M2 pair in the Lin-Lunin-Maldacena background, which can also be interpreted as a domain wall, and compare its basic properties with the expectations from its field theory description.