Effective Theory of Squeezed Correlation Functions
  Various inflationary scenarios can often be distinguished from one another by
looking at the squeezed limit behavior of correlation functions. Therefore, it
is useful to have a framework designed to study this limit in a more systematic
and efficient way. We propose using an expansion in terms of weakly coupled
super-horizon degrees of freedom, which is argued to generically exist in a
near de Sitter space-time. The modes have a simple factorized form which leads
to factorization of the squeezed-limit correlation functions with power-law
behavior in $k_{\rm long}/k_{\rm short}$. This approach reproduces the known
results in single-, quasi-single-, and multi-field inflationary models.
However, it is applicable even if, unlike the above examples, the additional
degrees of freedom are not weakly coupled at sub-horizon scales. Stronger
results are derived in two-field (or sufficiently symmetric multi-field)
inflationary models. We discuss the observability of the non-Gaussian 3-point
function in the large-scale structure surveys, and argue that the squeezed
limit behavior has a higher detectability chance than equilateral behavior when
it scales as $(k_{\rm long}/k_{\rm short})^\Delta$ with $\Delta<1$ -- where
local non-Gaussianity corresponds to $\Delta=0$.
