弦暴胀中的旁观者轴子与原初黑洞
Spectator Axions in String Inflation and Primordial Black Holes
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中文总结 AI 辅助
本研究探究弦理论纤维暴胀中轴子的动力学，发现亚普朗克衰变常数轴子多不影响曲率扰动功率谱，特定参数轴子可增强扰动以辅助原初黑洞成核。
中文摘要 AI 辅助
我们研究了轻量旁观者轴子对弦理论暴胀期间原初黑洞（PBHs）成核的影响。原初黑洞展现出独特新颖的现象学，可能构成观测到的暗物质。宇宙暴胀提供了产生原初黑洞的机制，但这类暴胀模型通常具有普朗克尺度的场偏移，需要紫外完备化为量子引力。弦理论为此提供了自然框架，其中纤维暴胀已被证实能产生原初黑洞，同时满足宇宙微波背景数据的约束。本研究探讨纤维暴胀期间轴子的动力学，发现了多样丰富的可能性，包括场空间中的转向和原初扰动的增强。我们发现，在大部分参数空间中，尤其是衰变常数远小于普朗克尺度（$f\nearrow M_{\rm Pl}$）的轴子，对曲率扰动功率谱的影响可忽略，表明模型整体具有鲁棒性。另一方面，衰变常数更大但仍为亚普朗克尺度（$f\nearrow {\rm O}(0.1) M_{\rm Pl}$）且非微扰势的指数小前置因子的轴子，可增强扰动增长，使实现原初黑洞成核所需的放大更易达成，有效在弦理论中实现了轴子辅助的原初黑洞。
英文摘要
We study the impact of light spectator axions on the seeding of primordial black holes (PBHs) during inflation in string theory. Primordial black holes exhibit unique and novel phenomenology, and may constitute the observed dark matter. Cosmic inflation provides a mechanism for producing them, but such inflation models typically feature Planckian field excursions, necessitating an ultraviolet completion into quantum gravity. String theory provides a natural framework for doing so, and indeed Fibre Inflation has been shown to produce PBHs while satisfying constraints from cosmic microwave background data. In this work we study the dynamics of axions during Fibre Inflation, and find a diverse and rich set of possibilities, including turns in field space and enhancement of primordial perturbations. We find that across most of parameter space, notably an axion with a far sub-Planckian decay constant $f\ll M_{\rm Pl}$, there is a negligible impact on the power spectrum of curvature perturbations, indicating an overall robustness of the model. On the other hand, an axion with a larger but still sub-Planckian decay constant, $f\gtrsim {\cal O}(0.1) M_{\rm Pl}$, and an exponentially small prefactor of its non-perturbative potential, can enhance the growth of perturbations, making it easier to achieve the amplification needed to seed PBHs, effectively realizing axion-assisted PBHs in string theory.
