Strongly Coupled Quasi-Single Field Inflation

TL;DR

This paper investigates the power spectrum in strongly coupled quasi-single field inflation, distinguishing local and non-local contributions, and develops effective field theory methods to simplify calculations while preserving key signals for cosmological insights.

Contribution

It introduces a partial effective field theory approach for strongly coupled inflation, enabling simplified calculations of the power spectrum with multiple massive propagators.

Findings

Local contribution dominates and is power-law suppressed by mass.

Non-local contribution is exponentially suppressed at large mass.

Standard clock signals are retained in the effective field theory approximation.

Abstract

We study the power spectrum of quasi-single field inflation where strong coupling is considered. The contribution from the massive propagator can be divided into local and non-local contributions. The local one is the leading contribution and is power-law suppressed as a function of mass, while the non-local contribution is exponentially suppressed in the large mass limit. For the local contribution, it is possible to use the effective field theory approach to study the power spectrum in the strongly coupled region of the parameter space. For the non-local contribution, we developed a partial effective field theory method to simplify the calculation: When there are multiple massive propagators, one can fully compute it after integrating out all but one massive propagator by effective field theory. The result retains the "standard clock" signal, which is interesting for probing the expansion history of the primordial universe and the physics of a "cosmological collider". The error involved compared to the full calculation is power law suppressed by the effective mass of the heavy field.