The Power Spectrum Of Primordial Gravitational Waves Generated by Anisotropic Metric

One of the predictions from simple inflation models is stochastic background of gravitational waves (or literally what is called the 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 amplified by inflation and generated by perturbing the Anisotropic (\emph{Bianchi type-I}) metric. We focus on the SED quantity of these gravity waves. The intended frameworks are the Einstein's and modified (pure quadratic \emph{Ricci} scalar) gravities. The spectral graphs for SED shows that in Einstein's gravity, the anisotropic model has the ability to adapt to the observational data (BBN bounds) and in the modified gravity, in addition to observational constraint adaptation, the scale-invariant character of the spectrum is much more pronounced.Comment: 8 pages, 3 figure. arXiv admin note: substantial text overlap with arXiv:1912.1247