探索作为粒子加速器的黑洞：环半径，目标粒子和逃逸条件
Exploring black holes as particle accelerators: hoop-radius, target particles and escaping conditions
摘要：
旋转黑洞可能是天然的粒子加速器的可能性一直是激烈争论的主题。虽然对于极端克尔黑洞，似乎可以达到任意高的质心能量，但一些研究指出，理论和天体物理的论点都将严重抑制可达到的能量。在这项工作中，我们研究克尔黑洞附近的粒子碰撞，通过审查和扩展到目前为止提出的方案。最值得注意的是，我们将把重点放在最近提出的目标粒子方案上，这些方案声称即使对于史瓦西黑洞也能达到任意高的能量。通过实施箍猜想，我们表明，这些方案涉及近地平线的目标粒子在原则上能够达到，次普朗克，但仍然超高的质量质心能量的顺序$10^{23}-10^{25}$ eV的非极值克尔黑洞。此外，通过分析这种碰撞中产生的粒子的性质，我们发现光子可以逃逸到无穷远。然而，它们的能量仅为碰撞粒子能量的量级，因此相对较低，这与先前文献中关于原始Bañados-Silk-West过程得出的结论相同。这一发现指出了碰撞彭罗斯过程的一般局限性，至少对于它们的初级产物而言是如此。
英文摘要：
The possibility that rotating black holes could be natural particle accelerators has been subject of intense debate. While it appears that for extremal Kerr black holes arbitrarily high center of mass energies could be achieved, several works pointed out that both theoretical as well as astrophysical arguments would severely dampen the attainable energies. In this work we study particle collisions near Kerr black holes, by reviewing and extending the so far proposed scenarios. Most noticeably, we shall focus on the recently advanced target particle scenarios which were claimed to reach arbitrarily high energies even for Schwarzschild black holes. By implementing the hoop conjecture we show that these scenarios involving near-horizon target particles are in principle able to attain, sub-Planckian, but still ultra-high center of mass energies of the order of $10^{23}-10^{25}$ eV even for non-extremal Kerr black holes. Furthermore, analysing the properties of particles produced in such collisions, we find that photons can escape to infinity. However, their energy is only of the order of the energy of the colliding particles and hence relatively low, which is the same conclusion previously reached in the literature about the original Bañados--Silk--West process. This finding points towards a general limitation of collisional Penrose processes, at least for what concerns their primary products.
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