Transdimensional tunneling in the multiverse

Topology-changing transitions between vacua of different effective dimensionality are studied in the context of a 6-dimensional Einstein-Maxwell theory. The landscape of this theory includes a 6d de Sitter vacuum (dS(6)), a number of dS(4) x S-2 and AdS(4) x S-2 vacua, and a number of AdS(2) x S-4 vacua. We find that compactification transitions dS(6) -> AdS(2) x S-4 occur through the nucleation of electrically charged black hole pairs, and transitions from dS(6) to dS(4) x S-2 and AdS(4) x S-2 occur through the nucleation of magnetically charged spherical black branes. We identify the appropriate instantons and describe the spacetime structure resulting from brane nucleation.