Luminal Propagation of Gravitational Waves in Scalar-tensor Theories: The Case for Torsion
arXiv:1910.00148 · doi:10.1103/PhysRevD.100.124039
Abstract
Scalar-tensor gravity theories with a nonminimal Gauss-Bonnet coupling typically lead to an anomalous propagation speed for gravitational waves, and have therefore been tightly constrained by multimessenger observations such as GW170817/GRB170817A. In this paper we show that this is not a general feature of scalar-tensor theories, but rather a consequence of assuming that spacetime torsion vanishes identically. At least for the case of a nonminimal Gauss-Bonnet coupling, removing the torsionless condition restores the canonical dispersion relation and therefore the correct propagation speed for gravitational waves. To achieve this result we develop a new approach, based on the first-order formulation of gravity, to deal with perturbations on these Riemann-Cartan geometries.
16 pages, 2 figures. v2: 17 pages, 2 figures, updated references. v3: 17 pages, 2 figures, minor changes, version accepted for publication in PRD
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