Tribrid inflation is a class of supersymmetric inflation models where the scalar component of a matter superfield, or a D-flat direction of matter fields, drives inflation. Similar to Hybrid inflation, the end of inflation is reached when a “waterfall field”, which was stabilized during inflation at a field value where the scalar potential features a large vacuum energy, starts rapidly rolling towards its minimum where a symmetry group G is spontaneously broken. In contrast to standard supersymmetric Hybrid inflation, where the inflaton is a gauge singlet, in Tribrid inflation it can be a gauge non-singlet, which, via its vacuum expectation value, already breaks the gauge symmetry. This raises the question whether topological defects can still form after inflation in this class of models, and if so, which types of defects are generated. We investigate this question systematically in realisations of Tribrid inflation where G = U(1) and we analyse under which conditions cosmic strings form. We find that in the considered cases where domain walls form, these are only temporary and do not invalidate the model realisations. We also discuss how our results can be used to analyse models of Tribrid inflation associated with the final step of SO(10) breaking, where cosmic strings can be metastable and provide a promising explanation of the recent PTA results hinting at a stochastic gravitational wave background at nanohertz frequencies.

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来自 Tribrid 膨胀的宇宙弦


Tribrid 膨胀是一类超对称膨胀模型，其中物质超场的标量分量或物质场的 D 平面方向驱动膨胀。与混合膨胀类似，当“瀑布场”在膨胀过程中稳定在标量势具有大真空能量的场值时，膨胀结束，开始迅速滚动到其最小值，对称群 G 自发打破。与标准的超对称混合膨胀相反，其中膨胀子是规范单重态，而在 Tribrid 膨胀中，它可以是规范非单重态，通过其真空期望值，它已经打破了规范对称性。这就提出了一个问题，在这类模型中，膨胀后是否还会形成拓扑缺陷，如果是这样，会产生哪些类型的缺陷。我们在 G = U（1） 的 Tribrid 膨胀的实现中系统地研究了这个问题，并分析了宇宙弦在哪些条件下形成。我们发现，在考虑形成域壁的情况下，这些只是暂时的，不会使模型实现无效。我们还讨论了如何使用我们的结果来分析与 SO（10） 断裂的最后一步相关的 Tribrid 膨胀模型，其中宇宙弦可以是亚稳态的，并为最近的 PTA 结果提供了有希望的解释，暗示了纳赫兹频率的随机引力波背景。