arXiv 1004.35582010-04hep-thastro-ph.COgr-qchep-ph

用精确黑洞物理探索弦轴宇宙

Exploring the String Axiverse with Precision Black Hole Physics

Asimina Arvanitaki, Sergei Dubovsky

备注：: 54 pages, 15 figures; v2: PRD version, small correction in eq. 48 and 53 as well as fig. 10, conclusions unchanged
发表信息：: Phys.Rev.D83:044026,2011
DOI：: 10.1103/PhysRevD.83.044026

摘要：

最近有人提出，存在大量的轻轴子，即一个轴宇宙，是弦论存在额外维度的证据。我们通过彭罗斯超辐射过程讨论了这些轴子对天体物理黑洞的观测结果。当一个轴子康普顿波长与黑洞的大小相当时，轴子与黑洞“核”结合，在天空中形成一个引力原子。由黑洞的能量和角动量提供的超辐射原子能级的占有数呈指数增长。黑洞向下旋转，在其周围形成一个轴子玻色-爱因斯坦凝聚体云。当吸引轴子的自相互作用变得比引力结合能更强时，轴子云坍塌，这种现象在凝聚态物理中被称为“Bosenova”。轴子的存在首先是由天体物理学上的黑洞的质量与自旋图中的空隙来诊断的。对于年轻的黑洞，自旋的允许值是量子化的，从而在能隙区域内产生“Regge轨迹”。轴子云也可以通过精确的近视界几何映射或通过来自Bosenova爆炸的引力波以及引力原子中的轴子跃迁和湮灭直接观察到。我们的估计表明，这些信号在即将到来的实验中是可以检测到的，例如先进的LIGO，AGIS和LISA。目前的黑洞自旋测量表明，QCD轴子衰变常数的上限为2 x 10^17 GeV，而高级LIGO可以检测到来自QCD轴子云的信号，其衰变常数与大统一尺度一样低。最后，我们讨论了观测与Bosenova爆炸有关的γ射线的可能性，也许，从QCD轴子到光子转换的无线电波。

英文摘要：

It has recently been suggested that the presence of a plenitude of light axions, an Axiverse, is evidence for the extra dimensions of string theory. We discuss the observational consequences of these axions on astrophysical black holes through the Penrose superradiance process. When an axion Compton wavelength is comparable to the size of a black hole, the axion binds to the black hole "nucleus" forming a gravitational atom in the sky. The occupation number of superradiant atomic levels, fed by the energy and angular momentum of the black hole, grows exponentially. The black hole spins down and an axion Bose-Einstein condensate cloud forms around it. When the attractive axion self-interactions become stronger than the gravitational binding energy, the axion cloud collapses, a phenomenon known in condensed matter physics as "Bosenova". The existence of axions is first diagnosed by gaps in the mass vs spin plot of astrophysical black holes. For young black holes the allowed values of spin are quantized, giving rise to "Regge trajectories" inside the gap region. The axion cloud can also be observed directly either through precision mapping of the near horizon geometry or through gravitational waves coming from the Bosenova explosion, as well as axion transitions and annihilations in the gravitational atom. Our estimates suggest that these signals are detectable in upcoming experiments, such as Advanced LIGO, AGIS, and LISA. Current black hole spin measurements imply an upper bound on the QCD axion decay constant of 2 x 10^17 GeV, while Advanced LIGO can detect signals from a QCD axion cloud with a decay constant as low as the GUT scale. We finally discuss the possibility of observing the gamma-rays associated with the Bosenova explosion and, perhaps, the radio waves from axion-to-photon conversion for the QCD axion.

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