电磁级联中普适光子谱的一个漏洞：对“宇宙学锂问题”的应用
A loophole to the universal photon spectrum in electromagnetic cascades: application to the "cosmological lithium problem"
摘要：
光子背景上的电磁级联的标准理论预测了由此产生的非热光子谱的准普适形状。这已经被应用到非常不同的领域，包括非热大爆炸核合成（BBN）。然而，一旦注入的光子的能量下降到对产生阈值以下，光谱形状就会非常不同，这是过去文献中忽略的事实。这个漏洞可能有重要的现象学后果，因为它一般改变了BBN边界上的非热遗迹：例如，它允许重新打开的可能性，纯电磁解决方案的所谓的“宇宙学锂问题”，这被认为是排除在其他宇宙学约束。我们证明了这一点的原理的例子和一个简单的粒子物理模型，与以前的文献相比。
英文摘要：
The standard theory of electromagnetic cascades onto a photon background predicts a quasi-universal shape for the resulting non-thermal photon spectrum. This has been applied to very disparate fields, including non-thermal big bang nucleosynthesis (BBN). However, once the energy of the injected photons falls below the pair-production threshold the spectral shape is very different, a fact that has been overlooked in past literature. This loophole may have important phenomenological consequences, since it generically alters the BBN bounds on non-thermal relics: for instance it allows to re-open the possibility of purely electromagnetic solutions to the so-called "cosmological lithium problem", which were thought to be excluded by other cosmological constraints. We show this with a proof-of-principle example and a simple particle physics model, compared with previous literature.
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