Anisotropic Stress as a Signature of Nonstandard Propagation of Gravitational Waves
Ippocratis D. SaltasSchool of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United KingdomIgnacy SawickiDépartment de Physique Théorique and Center for Astroparticle Physics, Université de Genève, Quai Ernest-Ansermet 24, CH-1211 Genève 4, Switzerland and African Institute for Mathematical Sciences, 6 Melrose Road, Muizenberg 7945, South AfricaLuca AmendolaIntitut für Theoretische Physik, Ruprecht-Karls-Universität Heidelberg, Philosophenweg 16, 69120 Heidelberg, GermanyM. KunzDépartment de Physique Théorique and Center for Astroparticle Physics, Université de Genève, Quai Ernest-Ansermet 24, CH-1211 Genève 4, Switzerland and African Institute for Mathematical Sciences, 6 Melrose Road, Muizenberg 7945, South Africa
2014en
ABI
Abstract
We make precise the heretofore ambiguous statement that anisotropic stress is a sign of a modification of gravity. We show that in cosmological solutions of very general classes of models extending gravity-all scalar-tensor theories (Horndeski), Einstein-aether models, and bimetric massive gravity-a direct correspondence exists between perfect fluids apparently carrying anisotropic stress and a modification in the propagation of gravitational waves. Since the anisotropic stress can be measured in a model-independent manner, a comparison of the behavior of gravitational waves from cosmological sources with large-scale-structure formation could, in principle, lead to new constraints on the theory of gravity.
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