Chern-Simons gravitational term coupled to a spectator field

TL;DR

This paper investigates the effects of a Chern-Simons gravitational term coupled to a massive spectator field during multi-field inflation, deriving parity-violating bispectra and analyzing their observational signatures.

Contribution

It introduces a novel coupling scenario with a spectator field, deriving the resulting parity-violating interactions and constraining their non-Gaussian signatures.

Findings

Parity-odd shapes in scalar-tensor bispectra are identified.

Perturbativity bounds constrain coupling strengths and non-Gaussianity amplitudes.

Distinctive parity-violating signatures could inform inflationary models.

Abstract

The Chern-Simons gravitational term is typically coupled to the inflaton field during inflation. In this work, we explore an alternative scenario where the Chern-Simons term is minimally coupled to a massive spectator field, $\sigma$, within a multi-field inflationary framework where the spectator field is linearly coupled to the inflaton. We derive the corresponding parity-violating cubic interaction Lagrangian involving the curvature, spectator and tensor perturbations and compute how it affects primordial scalar-tensor bispectra. We find that these correlators yield distinctive parity-odd shapes. Perturbativity and consistency bounds are derived, constraining the couplings and the amplitude of the associated non-Gaussianities.