Sakstein Jeremy, Jain Bhuvnesh
Department of Physics and Astronomy, Center for Particle Cosmology, University of Pennsylvania, 209 South 33rd Street, Philadelphia, Pennsylvania 19104, USA.
Phys Rev Lett. 2017 Dec 22;119(25):251303. doi: 10.1103/PhysRevLett.119.251303. Epub 2017 Dec 18.
The LIGO and VIRGO Collaborations have recently announced the detection of gravitational waves from a neutron star-neutron star merger (GW170817) and the simultaneous measurement of an optical counterpart (the γ-ray burst GRB 170817A). The close arrival time of the gravitational and electromagnetic waves limits the difference in speed of photons and gravitons to be less than about 1 part in 10^{15}. This has three important implications for cosmological scalar-tensor gravity theories that are often touted as dark energy candidates and alternatives to the Λ cold dark matter model. First, for the most general scalar-tensor theories-beyond Horndeski models-three of the five parameters appearing in the effective theory of dark energy can now be severely constrained on astrophysical scales; we present the results of combining the new gravity wave results with galaxy cluster observations. Second, the combination with the lack of strong equivalence principle violations exhibited by the supermassive black hole in M87 constrains the quartic galileon model to be cosmologically irrelevant. Finally, we derive a new bound on the disformal coupling to photons that implies that such couplings are irrelevant for the cosmic evolution of the field.
激光干涉引力波天文台（LIGO）和处女座干涉仪（VIRGO）合作团队最近宣布，他们探测到了来自中子星-中子星合并事件（GW170817）的引力波，并同时测量到了一个光学对应体（伽马射线暴GRB 170817A）。引力波和电磁波几乎同时到达，这将光子和引力子的速度差异限制在小于约10^15分之一。这对于常被吹捧为暗能量候选者以及Λ冷暗物质模型替代方案的宇宙学标量-张量引力理论有三个重要影响。首先，对于最一般的标量-张量理论——超越霍恩德斯基模型——暗能量有效理论中出现的五个参数中的三个，现在可以在天体物理尺度上受到严格限制；我们展示了将新的引力波结果与星系团观测相结合的结果。其次，结合M87中超大质量黑洞未表现出强烈等效原理违反这一情况，限制了四次伽利略子模型在宇宙学上的无关性。最后，我们推导出了一个关于与光子的非共形耦合的新界限，这意味着这种耦合与该场的宇宙演化无关。
