Asymptotic Symmetries in de Sitter and Inflationary Spacetimes
  Soft gravitons produced by the expansion of de Sitter can be viewed as the
Nambu-Goldstone bosons of spontaneously broken asymptotic symmetries of the de
Sitter spacetime. We explicitly construct the associated charges, and show that
acting with the charges on the vacuum creates a new state equivalent to a
change in the local coordinates induced by the soft graviton. While the effect
remains unobservable within the domain of a single observer where the symmetry
is unbroken, this change is physical when comparing different asymptotic
observers, or between a transformed and un-transformed initial state,
consistent with the scale-dependent statistical anisotropies previously derived
using semiclassical relations. We then compute the overlap, $\langle0|
0'\rangle$, between the unperturbed de Sitter vacuum $|0\rangle$, and the state
$| 0'\rangle$ obtained by acting $\mathcal{N}$ times with the charge. We show
that when $\mathcal{N}\to M_p^2/H^2$ this overlap receives order one
corrections and $\langle0| 0'\rangle\to 0$, which corresponds to an infrared
perturbative breakdown after a time $t_{dS} \sim M_p^2/H^3$ has elapsed,
consistent with earlier arguments in the literature arguing for a perturbative
breakdown on this timescale. We also discuss the generalization to inflation,
and rederive the 3-point and one-loop consistency relations.
