Influence of Unobservable Modes on Correlation Functions during
  Inflation
  Coupling between sub- and super-Hubble modes can affect the locally observed
statistics of our universe. In the context of Quasi-Single Field Inflation, we
can compute correlation functions and derive the influence of those
unobservable modes on observed correlation functions as well as on the inferred
cosmological parameters. We study how different classes of diagrams affect the
bispectrum in the squeezed limit; in particular, while contact-like diagrams
leave the scaling between the long and short modes unchanged, exchange-like
diagrams do modify the shape of the bispectrum. We show that the mass of the
hidden sector field can hence be biased by an unavoidable cosmic variance that
can reach a 1-$\sigma$ uncertainty of $\mathcal{O}(10\%)$ for a weakly
non-Gaussian universe. Finally, we go beyond the bispectrum and show how
couplings between unobservable and observable modes can affect generic
correlation functions with arbitrary order non-derivative self-interactions.
