We explore the irreducible cosmological implications of a singlet real scalar field. Our focus is on theories with an approximate and spontaneously broken ℤ2 symmetry where quasistable domain walls can form at early times. This seemingly simple framework bears a wealth of phenomenological implications that can be tackled by means of different cosmological and astrophysical probes. We elucidate the connection between domain wall dynamics and the production of dark matter and gravitational waves. In particular, we identify three main benchmark scenarios. The gravitational wave signal observed by pulsar timing arrays can be generated by the domain walls if the mass of the singlet is 𝑚𝑠∼PeV. For lower masses, but with 𝑚𝑠≳10  GeV, scalars produced in the annihilation of the domain walls can be dark matter with a distinctive feature in their power spectrum. Finally, the thermal bath provides an unavoidable source of unstable scalars via the freeze-in mechanism whose subsequent decays can be tested by their imprints on cosmological and terrestrial observables.

中文翻译：

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具有打破对称性的真实标量的不可简化宇宙学背景


我们探讨了单重态实标量场的不可约宇宙学意义。我们的重点是具有近似和自发打破的 Z2 对称性的理论，其中准稳态畴壁可以在早期形成。这个看似简单的框架具有丰富的现象学意义，可以通过不同的宇宙学和天体物理学探针来解决。我们阐明了域壁动力学与暗物质和引力波的产生之间的联系。具体而言，我们确定了三个主要的基准情景。如果单重态的质量为 ms∼PeV，则脉冲星计时阵列观察到的引力波信号可以由畴壁产生。对于质量较低但 ms≳10 GeV 的标量，在畴壁湮灭时产生的标量可以是暗物质，在其功率谱中具有明显的特征。最后，温泉浴通过冻结机制提供了不可避免的不稳定标量来源，其随后的衰变可以通过它们在宇宙学和地面观测物上的印记来测试。