The Influence of the Shear on the Gravitational Waves in the Early Anisotropic Universe

TL;DR

This paper investigates how shear affects gravitational waves in the early anisotropic universe, deriving equations that could explain observational anisotropies in primordial gravitational wave backgrounds.

Contribution

It derives the Raychaudhuri type equation for shear and expansion in an early anisotropic universe, linking shear evolution to gravitational wave anisotropies.

Findings

Derived shear evolution equations relevant to primordial gravitational waves

Connected shear effects to potential observational anisotropies in gravitational wave background

Provided theoretical framework for analyzing anisotropic early universe impacts

Abstract

We study the singularity of the congruences for both timelike and null geodesic curves using the expansion of the early anisotropic Bianchi type I Universe. In this paper, we concentrate on the influence of the shear of the timelike and null geodesic congruences in the early Universe. Under some natural conditions, we derive the Raychaudhuri type equation for the expansion and the shear-related equations. Recently, scientists working on the LIGO (Laser Interferometer Gravitational-Wave Observatory) have shown many possibilities to observing the anisotropy of the primordial gravitational wave background radiation. We deduce the evolution equation for the shear that may be responsible for those observational results.