Gravitational wave cosmology in general relativity and Einstein-scalar-Gauss-Bonnet gravity.

We study systematically gravitational wave (GW) cosmology in both Einstein’s General Relativity (GR) and Einstein-scalar-Gauss-Bonnet (EsGB) gravity. We first investigate the spacetime singularities of plane GWs in GR and find that only few of them are free of spacetime singularities. In particular, we show explicitly that in the BJR coordinates the singularity can be well described by the function χ ≡ (u − us)α ˆχ(u), and the spacetime is always singular except two cases α = 1/2 or 1. To study GWs propagating in our Universe, we show that in GR the spatial, traceless, and Lorentz gauge conditions can be imposed simultaneously, even when the background is not vacuum. Then, we calculate the gravitational integrated Sachs-Wolfe effects, whereby the dependences of the amplitude, phase and luminosity distance of GWs on the inhomogeneous universe are read out explicitly. In EsGB gravity both spin-0 and spin-2 gravitons exist. As a result, only the Lorenz and spatial gauges can be applied simultaneously. Assuming the speed cT of the spin-2 graviton is the same as that of photons, we find explicitly the stability conditions of the theory and then obtain the severest observational constraints found so far. The trajectories for both spin-2 and spin-0 gravitons and the amplitudes of GWs along the trajectories are explicitly obtained in homogeneous and isotropic universe. The amplitude of a spin-2 GW is practically indistinguishable from that of GR, while the spin-0 GWs remain almost constant during radiation- and matter-dominated epochs, and in the dark energy-dominated epoch it is proportional to the physical distance between the source and the observer. A careful analysis shows that the latter is due to the assumption cT = 1. When cT̸ = 1 to the extent that is consistent with the stability conditions and observational constraints, the above behavior disappears.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Doctoral

Grantor

Baylor University.

Year dc:date.issued

2025

Author dc:creator

• Li, Bowen, 1992-

Advisor dc:contributor.advisor

• Wang, Anzhong.

• Gravitational wave (GW)
• Cosmology.
• General relativity (GR)
• Einstein-scalar-Gauss-Bonnet (EsGB) gravity.

Statement dc:rights

• Baylor University works are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. Contact libraryquestions@baylor.edu for inquiries about permission.

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/2104/13835

OAI identifier oai:identifier

oai:baylor-ir.tdl.org:2104/13835