1. Superheavy quasi-stable strings and walls bounded by strings in the light of NANOGrav 15 year data
- Author
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Lazarides, George, Maji, Rinku, and Shafi, Qaisar
- Subjects
High Energy Physics - Phenomenology ,High Energy Physics - Phenomenology (hep-ph) ,Cosmology and Nongalactic Astrophysics (astro-ph.CO) ,FOS: Physical sciences ,Astrophysics - Cosmology and Nongalactic Astrophysics - Abstract
Composite topological structures such as ``superheavy quasi-stable strings" and ``walls bounded by strings" arise in realistic extensions of the Standard Model of high energy physics. We show that the gravitational radiation emitted in the early universe by these two unstable structures, with a dimensionless string tension $G\mu\approx 10^{-6}$, is consistent with the NANOGrav discovery of low frequency gravitational background, as well as the recent LIGO-VIRGO constraints, provided the superheavy strings and monopoles experience a certain amount of inflation. For the case of walls bounded by strings, the domain wall arises from the spontaneous breaking of a remnant discrete gauge symmetry around the electroweak scale. The quasi-stable strings, on the other hand, arise from a two step breaking of a local gauge symmetry. The monopoles appear from the first breaking and get connected to strings that arise from the second breaking. Both composite structures decay by emitting gravitational waves over a wide frequency range., Comment: 8 pages, 4 captioned figures
- Published
- 2023
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