InstiQuai Ernest Ansermettut für Theoretische Physik, Ruprecht-Karls-Universität Heidelberg, Philosophenweg 16, 69120 Heidelberg, Germany.
Départment de Physique Théorique and Center for Astroparticle Physics, Université de Genève, Quai Ernest Ansermet 24, CH-1211 Genéve 4, Switzerland.
Phys Rev Lett. 2018 Mar 30;120(13):131101. doi: 10.1103/PhysRevLett.120.131101.
The coincident detection of gravitational waves (GW) and a gamma-ray burst from a merger of neutron stars has placed an extremely stringent bound on the speed of GWs. We showed previously that the presence of gravitational slip (η) in cosmology is intimately tied to modifications of GW propagation. This new constraint implies that the only remaining viable source of gravitational slip is a conformal coupling to gravity in scalar-tensor theories, while viable vector-tensor theories cannot now generate gravitational slip at all. We discuss structure formation in the remaining viable models, demonstrating that (i) the dark-matter growth rate must now be at least as fast as in general relativity (GR), with the possible exception of that beyond the Horndeski model, and (ii) if there is any scale dependence at all in the slip parameter, it is such that it takes the GR value at large scales. We show a consistency relation that must be violated if gravity is modified.
引力波 (GW) 和来自中子星合并的伽马射线暴的同时探测，对 GW 的速度施加了极其严格的限制。我们之前曾表明，宇宙学中引力滑动 (η) 的存在与 GW 传播的修正密切相关。这一新的限制意味着引力滑动的唯一剩余可行来源是标量张量理论中对引力的共形耦合，而可行的矢量张量理论现在根本不能产生引力滑动。我们讨论了剩余可行模型中的结构形成，表明 (i) 现在暗物质增长率必须至少与广义相对论 (GR) 一样快，除了超越霍恩德斯基模型的情况，以及 (ii) 如果滑动参数存在任何尺度依赖性，那么它在大尺度上取 GR 值。我们展示了如果引力被修正，就必须违反的一致性关系。
