Luminal Scalar-Tensor theories for a not so dark Dark Energy
Abstract
In general the speed of Gravitational Waves (GWs) in Scalar-Tensor modifications of Einstein's gravity is different from the speed of Light. Nevertheless, it has been measured that their speeds are nearly the same. For the most general Scalar-Tensor theories classified to date that do propagate a graviton -- DHOST, {\it including Horndeski and Beyond Horndeski (BH) theories} -- we show that, remarkably, up to 5 self-consistent couplings of the scalar of Dark Energy (DE) to the Photon are enough to make their GWs luminal in a wide set of cases. We find at least one Luminal Beyond Horndeski theory for which the GW decay into Dark Energy is suppressed in any cosmological background.
Cite
@article{arxiv.2412.13460,
title = {Luminal Scalar-Tensor theories for a not so dark Dark Energy},
author = {S. Mironov and A. Shtennikova and M. Valencia-Villegas},
journal= {arXiv preprint arXiv:2412.13460},
year = {2025}
}
Comments
5 pages. Matches the version in PRD. Results unchanged. Expanded discussions in the final section