Dark energy after GW170817, revisited
Abstract
We revisit the status of scalar-tensor theories with applications to dark energy in the aftermath of the gravitational wave signal GW170817 and its optical counterpart GRB170817A. At the level of the cosmological background, we identify a class of theories, previously declared unviable in this context, whose anomalous gravitational wave speed is proportional to the scalar equation of motion. As long as the scalar field is assumed not to couple directly to matter, this raises the possibility of compatibility with the gravitational wave data, for any cosmological sources, thanks to the scalar dynamics. This newly "rescued" class of theories includes examples of generalised quintic galileons from Horndeski theories. Despite the promise of this leading order result, we show that the loophole ultimately fails when we include the effect of large scale inhomogeneities.
Keywords
Cite
@article{arxiv.1810.08239,
title = {Dark energy after GW170817, revisited},
author = {Edmund J. Copeland and Michael Kopp and Antonio Padilla and Paul M. Saffin and Constantinos Skordis},
journal= {arXiv preprint arXiv:1810.08239},
year = {2019}
}
Comments
Updated with corrections to the gravitational wave propagation coming from higher order terms in the presence of large scale inhomogeneities. These close off any remaining loopholes. References added