Vacuum Sampling in the Landscape during Inflation

We consider the phenomenological consequences of sampling multiple vacua during inflation motivated by an enormous landscape. A generic consequence of this sampling is the formation of domain walls, characterized by the scale $\mu$ of the barriers that partition the accessed vacua. We find that the success of Big Bang Nucleosynthesis (BBN) implies $\mu \gsim 10$ TeV, as long as the sampled vacua have a non-degeneracy larger than $\cal{O}({{\rm MeV}}^{\rm 4})$. Otherwise, the walls will dominate and eventually form black holes that must reheat the universe sufficiently for BBN to take place; in this case, we obtain $\mu \gsim 10^{-5}M_P$. These black holes are not allowed to survive and contribute to cosmic dark matter density.