Metastable Cosmic Strings and Gravitational Waves from Flavour Symmetry Breaking
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| Format: | Preprint |
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2025
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| _version_ | 1866915450952089600 |
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| author | Antusch, Stefan Hinze, Kevin Saad, Shaikh |
| author_facet | Antusch, Stefan Hinze, Kevin Saad, Shaikh |
| contents | Metastable cosmic strings (MSCSs) are among the best-fitting explanations of the 2023 pulsar timing array (PTA) signal for gravitational waves at nanohertz frequencies. We propose the novel possibility that a network of MSCSs generating this signal originates from the multi-step spontaneous breaking of a gauged flavour symmetry. As a specific example, we construct a model of $SU(2)$ flavour symmetry in the context of $SU(5)$ grand unification, where the $SU(2)$ acts exclusively on the first two generations of the matter 10-plet, such that it is ``right for leptons'' and allows for large lepton mixing. The model explains the mass hierarchies of the Standard Model fermions, and predicts the string scale of the MSCSs in a range compatible with the 2023 PTA signal. Cosmic inflation is associated with the latter step of (two-step) family symmetry breaking, and the phase transition ending inflation generates the cosmic string network. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2503_05868 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Metastable Cosmic Strings and Gravitational Waves from Flavour Symmetry Breaking Antusch, Stefan Hinze, Kevin Saad, Shaikh High Energy Physics - Phenomenology Cosmology and Nongalactic Astrophysics Metastable cosmic strings (MSCSs) are among the best-fitting explanations of the 2023 pulsar timing array (PTA) signal for gravitational waves at nanohertz frequencies. We propose the novel possibility that a network of MSCSs generating this signal originates from the multi-step spontaneous breaking of a gauged flavour symmetry. As a specific example, we construct a model of $SU(2)$ flavour symmetry in the context of $SU(5)$ grand unification, where the $SU(2)$ acts exclusively on the first two generations of the matter 10-plet, such that it is ``right for leptons'' and allows for large lepton mixing. The model explains the mass hierarchies of the Standard Model fermions, and predicts the string scale of the MSCSs in a range compatible with the 2023 PTA signal. Cosmic inflation is associated with the latter step of (two-step) family symmetry breaking, and the phase transition ending inflation generates the cosmic string network. |
| title | Metastable Cosmic Strings and Gravitational Waves from Flavour Symmetry Breaking |
| topic | High Energy Physics - Phenomenology Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2503.05868 |