Group velocity of gravitational waves in an expanding universe
Abstract
The group velocity of gravitational waves in a flat Friedman-Robertson-Walker universe is investigated. For plane waves with wavelength well inside the horizon, and a universe filled with an ideal fluid with the pressure to density ratio less than 1/3, the group velocity is greater than the velocity of light. As a result, a planar pulse of gravitational waves propagating through the universe during the matter/dark energy dominated era arrives to the observer with the peak shifted towards the forefront. For gravitational waves emitted by inspiralling supermassive black holes at the edge of the observable universe, the typical shift that remains after the effects of nonplanarity are suppressed is of order of ten picoseconds.
Keywords
Cite
@article{arxiv.0707.1513,
title = {Group velocity of gravitational waves in an expanding universe},
author = {Vladimír Balek and Vratko Polák},
journal= {arXiv preprint arXiv:0707.1513},
year = {2011}
}
Comments
19 pages, 2 figures; structure reorganized, discussion of electromagnetic waves altered