Probing pre-inflationary anisotropy with directional variations in the gravitational wave background

TL;DR

This paper investigates how pre-inflationary anisotropies could imprint distinctive angular patterns on the primordial gravitational-wave background, offering a potential observational probe through future all-sky gravitational wave measurements.

Contribution

It introduces a detailed analysis of anisotropic gravitational-wave backgrounds from a Kasner-like pre-inflationary phase, linking anisotropy patterns to observable signatures.

Findings

Angular distribution maps reveal topologically distinctive patterns based on anisotropy degree.

Future observations could detect these patterns to probe pre-inflationary universe.

Current limits from CMB B-mode polarization constrain anisotropic gravitational wave amplitudes.

Abstract

We perform a detailed analysis on a primordial gravitational-wave background amplified during a Kasner-like pre-inflationary phase allowing for general triaxial anisotropies. It is found that the predicted angular distribution map of gravitational-wave intensity on large scales exhibits topologically distinctive patterns according to the degree of the pre-inflationary anisotropy, thereby serving as a potential probe for the pre-inflationary early universe with future all-sky observations of gravitational waves. We also derive an observational limit on the amplitude of such anisotropic gravitational waves from the B-mode polarisation of the cosmic microwave background.