The speed of Galileon gravity
The speed of Galileon gravity
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伽利略引力的速度
DOI：
10.1088/1475-7516/2016/03/004
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发表时间：
2015
影响因子：
6.4
通讯作者：
A. Davis
中科院分区：
文献类型：
--
作者：
P. Brax;C. Burrage;A. Davis
我们分析了耦合伽利略模型中的引力波的速度，状态方程为ω ε =−1和无幽灵的闵可夫斯基极限。我们发现，引力波的传播速度比光速快得多，除非这些模型是立方Galileon的小扰动和Galileon能量密度是次主导的占主导地位的宇宙常数。在这种情况下，当与物质的耦合与Galileon拉格朗日量的立方项系数相联系时，引力波速度的双脉冲星边界可以满足，状态方程可以接近-1。这严重限制了伽利略模型所允许的宇宙学行为，我们不得不得出这样的结论：具有稳定闵可夫斯基极限的伽利略不能解释观测到的宇宙膨胀加速。此外，我们宇宙中任何次主导的伽利略分量都必须由立方项主导。对于这种引力子传播速度超过光速的模型，引力子可能变得不稳定，并可能衰变为光子对。它们也可以通过切伦科夫辐射发射光子。我们表明，这种快速的引力子到光子和切伦科夫辐射的衰减率实际上是可以忽略的。此外，引力信号和爆炸性天体物理事件发出的光之间的时间延迟可以证实引力的变化作用于宇宙的最大尺度。
We analyse the speed of gravitational waves in coupled Galileon models with an equation of state ωϕ=−1 now and a ghost-free Minkowski limit. We find that the gravitational waves propagate much faster than the speed of light unless these models are small perturbations of cubic Galileons and the Galileon energy density is sub-dominant to a dominant cosmological constant. In this case, the binary pulsar bounds on the speed of gravitational waves can be satisfied and the equation of state can be close to -1 when the coupling to matter and the coefficient of the cubic term of the Galileon Lagrangian are related. This severely restricts the allowed cosmological behaviour of Galileon models and we are forced to conclude that Galileons with a stable Minkowski limit cannot account for the observed acceleration of the expansion of the universe on their own. Moreover any sub-dominant Galileon component of our universe must be dominated by the cubic term. For such models with gravitons propagating faster than the speed of light, the gravitons become potentially unstable and could decay into photon pairs. They could also emit photons by Cerenkov radiation. We show that the decay rate of such speedy gravitons into photons and the Cerenkov radiation are in fact negligible. Moreover the time delay between the gravitational signal and light emitted by explosive astrophysical events could serve as a confirmation that a modification of gravity acts on the largest scales of the Universe.