Trans-Planckian Censorship and the Swampland
  In this paper, we propose a new Swampland condition, the Trans-Planckian
Censorship Conjecture (TCC), based on the idea that in a consistent quantum
theory of gravity sub-Planckian quantum fluctuations should remain quantum and
never become larger than the Hubble horizon and freeze in an expanding
universe. Applied to the case of scalar fields, it leads to conditions that are
similar to the refined dS Swampland conjecture. For large field ranges, TCC is
stronger than the dS Swampland conjecture but it is weaker for small field
ranges. In particular for asymptotic regions of field space, TCC leads to a
bound $|V'|\geq {2\over \sqrt{(d-1)(d-2)}}V$, which is consistent with all
known cases in string theory. Like the dS Swampland conjecture, the TCC forbids
long-lived meta-stable dS spaces, but it does allow sufficiently short-lived
ones.
