As a note, quantum-mechanical-branching many-worlds isn't actually particularly dominant in cosmological circles these days. Largely because it doesn't much impact cosmology. The multiple universes of the classic Many Worlds do not interact, and so are not interesting.

There are other multiple-universe theories out there, a couple of which still include multiple versions of a given individual, but which have potential for interaction between universes. These are the ones cosmologists care about.