Bounds on EFT's in an expanding Universe

TL;DR

This paper derives bounds on the Wilson coefficients of effective field theories in an expanding universe by analyzing mode propagation and spatial shifts, ensuring consistency within the EFT's regime of validity.

Contribution

It introduces a novel method to constrain EFT parameters in cosmological settings using mode propagation and spatial shift analysis.

Findings

Bounds on Wilson coefficients for EFTs in expanding universes

Constraints on shift-symmetric scalars and Galileons

Method applicable within the EFT's validity regime

Abstract

We find bounds on the Wilson coefficients of effective field theories (EFTs) living in a Universe undergoing expansion by requiring that its modes do not propagate further than a minimally coupled photon by a resolvable amount. To do so, we compute the spatial shift suffered by the EFT modes at a fixed time slice within the WKB approximation and the regime of validity of the EFT. We analyze the bounds arising on shift-symmetric scalars and curved space generalizations of Galileons.