Imprints of primordial gravitational waves with non-Bunch-Davies initial states on CMB bispectra

TL;DR

This paper investigates how non-Bunch-Davies initial states of primordial gravitational waves influence CMB bispectra, finding that tensor mode enhancements may be detectable under certain gravitational theories, unlike scalar modes.

Contribution

It demonstrates that tensor mode enhancements from non-Bunch-Davies states can be partially observable, contrasting with scalar modes, and provides examples of theories with detectable effects.

Findings

Tensor mode enhancements are partially reduced but can be detectable.

Scalar mode enhancements are less observable in CMB bispectra.

Certain gravitational theories predict detectable non-Bunch-Davies effects.

Abstract

It has been shown that both scalar and tensor modes with non-Bunch-Davies initial states can enhance the amplitudes of the primordial bispectra compared to those with the Bunch-Davies state, especially for wavenumber modes in a flattened triangle configuration. However, in the case of the non-Bunch-Davies scalar modes, it has also been found that those enhancements in Fourier space are somewhat reduced in bispectra of cosmic microwave background (CMB) fluctuations. In this paper, we show that the enhancement resulting from the tensor modes is partially reduced to a degree differing from that of the scalar modes, which makes the non-Bunch-Davies effects unobservable in gravitational theories with the same quadratic and cubic operators of the tensor perturbations as general relativity. Furthermore, we present examples of gravitational theories yielding enhancements that would potentially be detected through CMB experiments.