Eternal Inflation and the Refined Swampland Conjecture
  I apply recently proposed "Swampland" conjectures to eternal inflation in
single-scalar field theories. Eternal inflation is a phase of infinite
self-reproduction of a quasi-de Sitter universe which has been argued to be a
generic consequence of cosmological inflation. The originally proposed de
Sitter swampland conjectures were shown by Matsui and Takahashi and by
Dimopoulos to be generically incompatible with eternal inflation. However, the
more recently proposed "refined" swampland conjecture imposes a slightly weaker
criterion on the scalar field potential in inflation, and is consistent with
the existence of a tachyonic instability. In this paper, I show that eternal
inflation is marginally consistent with the refined de Sitter swampland
conjecture. Thus, if the refined conjecture is correct, the existence of a
landscape-based "multiverse" in string theory is not incompatible with a
self-consistent ultraviolet completion, with significant consequences for model
building in string theory.
