Bhattacharya Sourav, Dialektopoulos Konstantinos F, Romano Antonio Enea, Tomaras Theodore N
ITCP and Department of Physics, University of Crete, 70013 Heraklion, Greece.
Phys Rev Lett. 2015 Oct 30;115(18):181104. doi: 10.1103/PhysRevLett.115.181104. Epub 2015 Oct 29.
A step-by-step approach is followed to study cosmic structures in the context of Brans-Dicke theory with positive cosmological constant Λ and parameter ω. First, it is shown that regular stationary black-hole solutions not only have constant Brans-Dicke field ϕ, but can exist only for ω=∞, which forces the theory to coincide with the general relativity. Generalizations of the theory in order to evade this black-hole no-hair theorem are presented. It is also shown that in the absence of a stationary cosmological event horizon in the asymptotic region, a stationary black-hole horizon can support a nontrivial Brans-Dicke hair. Even more importantly, it is shown next that the presence of a stationary cosmological event horizon rules out any regular stationary solution, appropriate for the description of a star. Thus, to describe a star one has to assume that there is no such stationary horizon in the faraway asymptotic region. Under this implicit assumption generic spherical cosmic structures are studied perturbatively and it is shown that only for ω>0 or ω≲-5 their predicted maximum sizes are consistent with observations. We also point out how, many of the conclusions of this work differ qualitatively from the Λ=0 spacetimes.
我们采用逐步推进的方法，在具有正宇宙学常数Λ和参数ω的布兰斯 - 迪克理论背景下研究宇宙结构。首先，研究表明正则静态黑洞解不仅具有恒定的布兰斯 - 迪克场ϕ，而且仅在ω = ∞时才可能存在，这使得该理论与广义相对论一致。文中还给出了为规避此黑洞无毛定理而对该理论进行的推广。研究还表明，在渐近区域不存在静态宇宙事件视界的情况下，静态黑洞视界可以支持非平凡的布兰斯 - 迪克毛发。更重要的是，接下来研究表明，静态宇宙事件视界的存在排除了任何适用于描述恒星的正则静态解。因此，为了描述一颗恒星，必须假设在遥远的渐近区域不存在这样的静态视界。在这个隐含假设下，对一般的球形宇宙结构进行微扰研究，结果表明只有当ω > 0或ω≲ - 5时，它们预测的最大尺寸才与观测结果一致。我们还指出，这项工作的许多结论在定性上与Λ = 0的时空情况不同。
