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早期宇宙中原始黑洞对磁单极子的引力俘获

Gravitational capture of magnetic monopoles by primordial black holes in the early universe

Chen Zhang, Xin Zhang

备注：
42 pages, 1 figure. v3: Match the published version
发表信息：
JHEP 10 (2023) 037
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AI总结：

本文重新分析了早期宇宙中原始黑洞对磁单极子的引力俘获过程，通过正确建模扩散俘获截面，发现该机制无法显著降低磁单极子密度，但PBH形成时的磁荷涨落可能产生具有观测相关性的长寿命近极端磁黑洞。

摘要：

一个引人深思的问题是，早期宇宙中原始黑洞（PBHs）的存在是否可以通过引力俘获显著降低某些稳定大质量粒子（SMP）的丰度，随后 PBHs 在 BBN 之前蒸发以避免与严格的限制条件相冲突。例如，这一机制与 Stojkovic 和 Freese 提出的关于磁单极子问题的另一种解决方案相关，在该方案中，早期宇宙中产生的磁单极子被 PBHs 俘获，从而使暴胀免于必须在产生磁单极子的相变期间或之后发生。在这项工作中，我们通过以与共存磁单极子湮灭相同的方式对俘获过程进行建模，重新分析了该解决方案。以往文献中未得到妥善处理的一个微妙问题是扩散俘获的有效俘获截面的选择。我们对这一方面进行了正确的建模并论证了我们的处理方法。假设了单色 PBH 质量函数以及 PBH 蒸发之前的辐射主导期。我们发现，对于对称性破缺能标介于 $10^{10}\,\ ext{GeV}$ 和 $10^{15}\,\ ext{GeV}$ 之间的 Pati-Salam 磁单极子，其俘获率比导致磁单极子密度显著降低所需的水平低许多个数量级。在我们的假设范围内，我们还发现，足以使极端磁黑洞在宇宙学上保持稳定的磁荷，无法通过磁单极子俘获引起的磁荷涨落来获得。然而，宇宙学稳定性所需的大磁荷可以从 PBH 形成时的磁荷涨落中获得，并且如果随后磁单极子的丰度可以通过某种非暴胀机制被显著降低，则可能会产生具有观测相关性的、长寿命的近极端磁黑洞。

英文摘要：

It is intriguing to ask whether the existence of primordial black holes (PBHs) in the early universe could significantly reduce the abundance of certain stable massive particles (SMP) via gravitational capture, after which the PBHs evaporate before BBN to avoid conflict with stringent bounds. For example, this mechanism is relevant to an alternative solution of the monopole problem proposed by Stojkovic and Freese, in which magnetic monopoles produced in the early universe are captured by PBHs, thus freeing inflation from having to occur during or after the corresponding phase transitions that produced the monopoles. In this work, we reanalyze the solution by modelling the capture process in the same way as the coexisting monopole annihilation. A subtle issue which is not handled properly in the previous literature is the choice of an effective capture cross section for diffusive capture. We model this aspect properly and justify our treatment. A monochromatic PBH mass function and a radiation-dominated era before PBH evaporation are assumed. We find that for Pati-Salam monopoles corresponding to a symmetry breaking scale between $10^{10}\,\text{GeV}$ and $10^{15}\,\text{GeV}$, the capture rate is many orders of magnitude below what is needed to cause a significant reduction of the monopole density. Within our assumptions, we also find that the magnetic charge that is large enough to make an extremal magnetic black hole cosmologically stable cannot be obtained from magnetic charge fluctuation via monopole capture. The large magnetic charged required by cosmological stability can nevertheless be obtained from magnetic charge fluctuation at PBH formation, and if later the monopole abundance can be reduced significantly by some non-inflationary mechanism, long-lived near-extremal magnetic black holes of observational relevance might result.

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