Stochastic gravitational wave background anisotropies from inflation with non-Bunch-Davies states

TL;DR

This paper investigates how non-Bunch-Davies initial states during inflation can enhance anisotropies in the stochastic gravitational wave background, potentially making them detectable in future experiments.

Contribution

It formulates the primordial tensor bispectrum in Horndeski theory with non-Bunch-Davies states, showing potential enhancement of SGWB anisotropies beyond standard models.

Findings

Enhanced SGWB anisotropies due to non-Bunch-Davies states.

Explicit formulation of the tensor bispectrum in Horndeski theory.

Discussion on the detectability of these anisotropies in future experiments.

Abstract

It is known that stochastic gravitational wave backgrounds (SGWBs) have anisotropies generated by squeezed-type tensor non-Gaussianities originating from scalar-tensor-tensor (STT) and tensor-tensor-tensor cubic interactions. While the squeezed tensor non-Gaussianities in the standard slow-roll inflation with the Bunch-Davies vacuum state are suppressed due to the so-called consistency relation, those in extended models with the violation of the consistency relation can be enhanced. Among such extended models, we consider the inflation model with the non-Bunch-Davies state that is known to enhance the squeezed tensor non-Gaussianities. We explicitly formulate the primordial STT bispectrum induced during inflation in the context of Horndeski theory with the non-Bunch-Davies state and show that the induced SGWB anisotropies can be enhanced. We then discuss the detectability of those anisotropies in future gravitational wave experiments.