Local observer effect on the cosmological soft theorem

Understand

Non-Gaussianities of primordial perturbations in the soft limit provide the important information about the light degrees of freedom during inflation.

• The soft modes of the curvature perturbations, unobservable for a local observer, act as rescaling the spatial coordinates.
• We determine how the trispectrum in the collapsed limit is shifted by the rescaling due to the soft modes.
• We find the form of the inequality between $f_{\rm NL}$ and $\tau_{\rm NL}$ parameters is not affected by the rescaling, demonstrating that the role of the inequality as an indicator of the light degrees of freedom remains intact.