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arXiv 2108.13245hep-thhep-ph
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非最小引力耦合缓解的轴子质量问题

Axion Quality Problem Alleviated by Non-Minimal Coupling to Gravity

Koichi Hamaguchi, Yoshiki Kanazawa, Natsumi Nagata

摘要:

全球的对称性预计将违反重力,这可能会导致一个严重的问题,基于这些对称性的模型。一个著名的例子是QCD轴子模型中强CP问题的Peccei-Quinn解;它需要高质量地遵守整体U(1)对称性,甚至违反U(1)对称性的普朗克尺度抑制算子也会破坏这个解。事实上,我们知道引力瞬子确实破坏了U(1)佩西-奎因对称性,并导致了U(1)-破坏算符,将强CP问题带回到轴子模型中。然而,这个结论高度依赖于普朗克尺度周围的理论结构,因此,如果我们超越最小设置,就可能被回避。本文研究了Peccei-Quinn场与引力场的非最小耦合$ξ$对引力瞬子效应的影响。这种设置在宇宙学中经常被考虑,因为如果$ξ\lesssim 10^5$,它可以实现成功的暴胀。我们发现对于$ξ\gtrsim 2 \times 10^3$,引力瞬子的U(1)破缺效应可以被充分抑制,这表明即使在引力存在的情况下,U(1)对称性也可以保持高质量.因此,我们的结果指出了一个新的途径,以避免质量问题的整体对称性。

英文摘要:

Global symmetries are expected to be violated by gravity, which may cause a serious problem to models based on these symmetries. A famous example is the Peccei-Quinn solution to the strong CP problem in QCD axion models; it requires a global U(1) symmetry to be respected with high quality, and even the Planck-scale suppressed operators that violate the U(1) symmetry would spoil this solution. Indeed, it is known that gravitational instantons do break the U(1) Peccei-Quinn symmetry and induce the U(1)-violating operators, bringing back the strong CP problem to the axion models. This conclusion is, however, dependent highly on the structure of the theory around the Planck scale and, therefore, may be evaded if we go beyond the minimal setup. In this paper, we study the effect of a non-minimal coupling of the Peccei-Quinn field to gravity, $ξ$, on the gravitational instanton effect. This setup is frequently considered in cosmology as it can realize a successful inflation if $ξ\lesssim 10^5$. We find that the U(1)-breaking effect of the gravitational instantons can sufficiently be suppressed for $ξ\gtrsim 2 \times 10^3$, which suggests that the U(1) symmetry may be maintained with high quality even in the presence of gravity. Our result thus points to a new way to avoid the quality problem of global symmetries.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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