The Power Spectrum Of Gravitational Waves in Anisotropic Universe (\emph{Bianchi type--I})

TL;DR

This paper investigates how primordial gravitational waves' power spectrum differs in anisotropic Bianchi type-I universes compared to isotropic models, with implications for early universe cosmology and potential detection.

Contribution

It introduces a detailed analysis of the gravitational wave power spectrum in anisotropic Bianchi type-I universes during the radiation-dominated era, highlighting differences from isotropic models.

Findings

Power spectra differ in early universe for anisotropic vs. isotropic models.

Spectra converge to the same at present time.

Results inform early universe physics and gravitational wave detection strategies.

Abstract

One of the predictions from simple inflation models is stochastic background of Gravitational Waves (\textbf{GW}), or literally what is called Primordial Gravitational Waves (\textbf{PGW}) with a nearly scale--invariant spectrum. To discuss a possible direct detection of PGW, the quantity so--called Spectral Energy Density (\textbf{SED}) has crucial role. In this work, we consider PGW produced in the Radiation-Dominate(\textbf{RD}) era and generated by perturbing the isotropic and Anisotropic (\emph{Bianchi type--I}) metrics and focusing on the SED generated by these GW. This study was done because the power spectrum of GW from the RD epoch is one of the most important topics in early cosmology, as GW produced during this period can provide us with direct information about very High Energies and fundamental phases of the universe (e.g. inflation and phase transition)The results show that the power spectrums in the early universe are diffetent for isotropic and anisotropic universe, but they coincide at the present time.