Boost Breaking in the EFT of Inflation

TL;DR

This paper extends the Effective Field Theory of Multifield Inflation to include light Goldstone bosons from boost symmetry breaking, predicting their mass and exploring their interactions with curvature fluctuations for potential non-Gaussian signals.

Contribution

It introduces a new framework incorporating boost Goldstone bosons into inflation EFT, predicting their mass and analyzing their interactions with curvature fluctuations.

Findings

Goldstone bosons from boost breaking have mass ~√2H

Couplings lead to potential non-Gaussian signals

Framework predicts self-interacting particles during inflation

Abstract

If time-translations are spontaneously broken, so are boosts. This symmetry breaking pattern can be non-linearly realized by either just the Goldstone boson of time translations, or by four Goldstone bosons associated with time translations and boosts. In this paper we extend the Effective Field Theory of Multifield Inflation to consider the case in which the additional Goldstone bosons associated with boosts are light and coupled to the Goldstone boson of time translations. The symmetry breaking pattern forces a coupling to curvature so that the mass of the additional Goldstone bosons is predicted to be equal to $\sqrt{2}H$ in the vast majority of the parameter space where they are light. This pattern therefore offers a natural way of generating self-interacting particles with Hubble mass during inflation. After constructing the general effective Lagrangian, we study how these particles mix and interact with the curvature fluctuations, generating potentially detectable non-Gaussian signals.