Cosmic strings and domain walls: the impact of CMB $B$-mode data
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| Format: | Preprint |
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2026
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| _version_ | 1866911484205858816 |
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| author | Caloni, Luca Ferreira, Ricardo Z. Sousa, Lara Winckler, Clara |
| author_facet | Caloni, Luca Ferreira, Ricardo Z. Sousa, Lara Winckler, Clara |
| contents | We analyse CMB constraints on stable networks of cosmic strings and domain walls using for the first time full Planck 2018 data together with BICEP/Keck 2018 $B$-mode measurements. The defect-induced anisotropies are computed using the Unconnected Segment Model for Nambu-Goto and Abelian-Higgs strings, as well as for stable domain walls, and included in a full Markov Chain Monte Carlo analysis jointly varying all $Λ$CDM parameters, the tensor-to-scalar ratio, and the string/domain wall tension. No statistically significant evidence for defects is found, although we observe a mild preference for non-zero cosmic string tension. Our results improve previous constraints on the defect power spectrum by up to a factor of two. In the particular case of strings, the improvement is driven by the $B$-mode data, and is especially pronounced for Abelian-Higgs strings. We also present forecasts for the Simons Observatory and the LiteBIRD satellite: the former will improve string tension constraints by about a factor of three, while the latter those on the domain wall tension by about a factor of ten. Finally, we assess the impact of Nambu-Goto string loops on CMB anisotropies in light of both current and future observations. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2602_20050 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Cosmic strings and domain walls: the impact of CMB $B$-mode data Caloni, Luca Ferreira, Ricardo Z. Sousa, Lara Winckler, Clara Cosmology and Nongalactic Astrophysics High Energy Physics - Phenomenology We analyse CMB constraints on stable networks of cosmic strings and domain walls using for the first time full Planck 2018 data together with BICEP/Keck 2018 $B$-mode measurements. The defect-induced anisotropies are computed using the Unconnected Segment Model for Nambu-Goto and Abelian-Higgs strings, as well as for stable domain walls, and included in a full Markov Chain Monte Carlo analysis jointly varying all $Λ$CDM parameters, the tensor-to-scalar ratio, and the string/domain wall tension. No statistically significant evidence for defects is found, although we observe a mild preference for non-zero cosmic string tension. Our results improve previous constraints on the defect power spectrum by up to a factor of two. In the particular case of strings, the improvement is driven by the $B$-mode data, and is especially pronounced for Abelian-Higgs strings. We also present forecasts for the Simons Observatory and the LiteBIRD satellite: the former will improve string tension constraints by about a factor of three, while the latter those on the domain wall tension by about a factor of ten. Finally, we assess the impact of Nambu-Goto string loops on CMB anisotropies in light of both current and future observations. |
| title | Cosmic strings and domain walls: the impact of CMB $B$-mode data |
| topic | Cosmology and Nongalactic Astrophysics High Energy Physics - Phenomenology |
| url | https://arxiv.org/abs/2602.20050 |