transplanckian axions!
Transplanckian axions !?
摘要：
我们讨论了爱因斯坦理论中的量子引力效应与周期性轴子标量的耦合，以分析实现超普朗克轴子周期（又名衰变常数）的几种建议的可行性及其在大场膨胀模型中的可能应用。我们研究的效应对应于在轴子下带电的欧几里得引力瞬子的成核，我们的结果基本上与弱引力猜想相容（但独立于弱引力猜想），如下：具有超普朗克周期的单轴子理论包含引力瞬子，在轴子势中诱导相当大的高次谐波，这破坏了超普朗克暴胀子场范围。类似的结果也适用于晶格排列的多轴子模型（如Kim-Nilles-Peloso模型）。最后，具有$N$轴子的理论仍然可以实现适度的超普朗克周期性（通过$\sqrt{N}$因子），在轴子势中没有更高的谐波。弱引力猜想在这种情况下不成立，因为不存在一些瞬子，而这些瞬子是离散的$\mathbf{Z}_N$规范对称性所禁止的。最后我们讨论了这些瞬子在弦紧化中作为欧几里得D-膜的实现。
英文摘要：
We discuss quantum gravitational effects in Einstein theory coupled to periodic axion scalars to analyze the viability of several proposals to achieve superplanckian axion periods (aka decay constants) and their possible application to large field inflation models. The effects we study correspond to the nucleation of euclidean gravitational instantons charged under the axion, and our results are essentially compatible with (but independent of) the Weak Gravity Conjecture, as follows: Single axion theories with superplanckian periods contain gravitational instantons inducing sizable higher harmonics in the axion potential, which spoil superplanckian inflaton field range. A similar result holds for multi-axion models with lattice alignment (like the Kim-Nilles-Peloso model). Finally, theories with $N$ axions can still achieve a moderately superplanckian periodicity (by a $\sqrt{N}$ factor) with no higher harmonics in the axion potential. The Weak Gravity Conjecture fails to hold in this case due to the absence of some instantons, which are forbidden by a discrete $\mathbf{Z}_N$ gauge symmetry. Finally we discuss the realization of these instantons as euclidean D-branes in string compactifications.
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