Influence of Unobservable Modes on Correlation Functions during Inflation

Understand

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.