arXiv 2201.006812022-01-03hep-phastro-ph.CO

Peccei-Quinn对称性破缺对QCD轴子暗物质的宇宙学效应

Cosmological effects of Peccei-Quinn symmetry breaking on QCD axion dark matter

Kwang Sik Jeong, Kohei Matsukawa, Shota Nakagawa, Fuminobu Takahashi

备注：: 28 pages, 16 figures
DOI：: 10.1088/1475-7516/2022/03/026

摘要：

研究了Peccei-Quinn显式破缺对QCD轴子暗物质的宇宙学效应。我们发现，轴子丰度的减少或增加显着取决于初始位置，即使是一个微小的Peccei-Quinn打破，满足实验约束的中子电偶极测量。如果轴子首先开始围绕一个错误的真空振荡，并且如果它被困在那里，直到由于非微扰QCD效应导致假真空消失，它的丰度会显著增加，并且与衰变常数$f_a$无关，正如[JHEP 06（2016）150]中首次指出的那样。因此，即使衰变常数接近恒星冷却参数的下限，由俘获机制产生的轴子也可以解释暗物质。另一方面，如果轴子开始在接近低能真空的势能最小值附近振荡，由于绝热抑制机制，它的丰度会显著降低。这放宽了轴子窗口的上限，使$f_a$的值更大。我们还讨论了如何轴等曲率扰动的Peccei-Quinn破碎项的影响，并表明它可以被抑制在这两个政权。特别地，与传统场景相比，对于$f_a \lesssim 10^{11}{\rm GeV}$，膨胀尺度上的等曲率界限被放宽了许多数量级。

英文摘要：

We study cosmological effects of explicit Peccei-Quinn breaking on the QCD axion dark matter. We find that the axion abundance decreases or increases significantly depending on the initial position, even for a tiny Peccei-Quinn breaking that satisfies the experimental bound of the neutron electric dipole measurements. If the axion first starts to oscillate around a wrong vacuum and if it gets trapped there until the false vacuum disappears due to non-perturbative QCD effects, its abundance increases significantly and is independent of the decay constant $f_a$, as first pointed out in [JHEP 06 (2016) 150]. Thus, the axion produced by the trapping mechanism can explain dark matter even when the decay constant is close to the lower limit due to stellar cooling arguments. On the other hand, if the axion starts to oscillate about a potential minimum close to the low-energy vacuum, its abundance is significantly reduced because of the adiabatic suppression mechanism. This relaxes the upper limit of the axion window to large values of $f_a$. We also discuss how the axionic isocurvature perturbation is affected by the Peccei-Quinn breaking term, and show that it can be suppressed in both regimes. In particular, the isocurvature bound on the inflation scale is relaxed by many orders of magnitudes for $f_a \lesssim 10^{11}{\rm GeV}$ compared to the conventional scenario.

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