Cosmological observables, IR growth of fluctuations, and scale-dependent
  anisotropies
  We extend semiclassical methods in inflationary cosmology that capture
leading IR corrections to correlators. Such large IR effects can be absorbed
into a coordinate change when examining sufficiently local observables, but not
when comparing observations at large separation in scales, such as seen by a
late-time observer. The analysis is facilitated by definition of a
scale-dependent metric and physical momentum. These assist definition of
"IR-safe" observables seen by a post-inflationary observer, which are
contrasted to those based on the local geometry of the reheating surface. For
such observables, the observer's horizon provides an effective IR cutoff. IR
growth contributes to enhanced statistical inhomogeneities/anisotropies at
short scales, observation of which by a present day observer might be sought in
21 cm measurements. Such IR corrections are argued to grow large for a very
late-time observer.
