Hiramatsu Takashi, Ibe Masahiro, Suzuki Motoo
ICRR, The University of Tokyo, Kashiwa, Chiba 277-8582 Japan.
Department of Physics, Rikkyo University, Toshima, Tokyo 171-8501 Japan.
J High Energy Phys. 2020;2020(9):54. doi: 10.1007/JHEP09(2020)054. Epub 2020 Sep 7.
In our previous work, we found new types of the cosmic string solutions in the Abelian-Higgs model with an enhanced U(1) global symmetry. We dubbed those solutions as the compensated/uncompensated strings. The compensated string is similar to the conventional cosmic string in the Abrikosov-Nielsen-Olesen (ANO) string, around which only the would-be Nambu-Goldstone (NG) boson winds. Around the uncompensated string, on the other hand, the physical NG boson also winds, where the physical NG boson is associated with the spontaneous breaking of the enhanced symmetry. Our previous simulation in the 2+1 dimensional spacetime confirmed that both the compensated/uncompensated strings are formed at the phase transition of the symmetry breaking. Non-trivial winding of the physical NG boson around the strings potentially causes the so-called axion domain- wall problem when the model is applied to the axion model. In this paper, we perform simulation in the 3+1 dimensional spacetime to discuss the fate of the uncompensated strings. We observe that the evolution of the string-network is highly complicated in the 3+1 dimensional simulation compared with that seen in the previous simulation. Despite such complications, we find that the number of the uncompensated strings which could cause can be highly suppressed at late times. Our observation suggests that the present setup can be applied to the axion model without suffering from the axion domain-wall problem.
在我们之前的工作中，我们在具有增强的U(1)全局对称性的阿贝尔 - 希格斯模型中发现了新型的宇宙弦解。我们将这些解称为补偿/未补偿弦。补偿弦类似于阿布里科索夫 - 尼尔森 - 奥尔斯en（ANO）弦中的传统宇宙弦，在其周围只有准南布 - 戈德斯通（NG）玻色子缠绕。另一方面，在未补偿弦周围，物理NG玻色子也会缠绕，其中物理NG玻色子与增强对称性的自发破缺相关。我们之前在2 + 1维时空的模拟证实，补偿/未补偿弦都是在对称破缺的相变过程中形成的。当该模型应用于轴子模型时，物理NG玻色子围绕弦的非平凡缠绕可能会导致所谓的轴子畴壁问题。在本文中，我们在3 + 1维时空进行模拟，以讨论未补偿弦的命运。我们观察到，与之前的模拟相比，弦网络在3 + 1维模拟中的演化高度复杂。尽管存在这些复杂性，但我们发现，在后期，可能导致问题的未补偿弦的数量可以被高度抑制。我们的观察表明，当前的设置可以应用于轴子模型而不会受到轴子畴壁问题的困扰。
