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arXiv · 2601.04320

Metastable cosmic strings are broken at the start

Lorenzo Tranchedone·Ethan Carragher·Edward Hardy·Natálie Koscelanská van IJcken
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Abstract

We show that metastable cosmic strings break at early times, either via finite-temperature effects or by attaching to pre-existing monopoles during network percolation. The resulting segments can be initially super-horizon in size and thus persist for a significant amount of time. If the strings do not re-percolate, the network's eventual destruction is typically due to this early-time breaking rather than late-time quantum tunnelling. Survival of strings to epochs probed by NANOGrav requires $m_M^2/\mu\gtrsim 10^3$, where $m_M$ and $\mu$ are the monopole mass and the string tension respectively, over an order of magnitude larger than previous estimates. We also revisit quantum-tunnelling induced breaking. Results from numerical simulations suggest that this occurs mainly at rare high-tension points on the strings, yielding a rate much larger than is usually assumed. We briefly discuss the related scenario of flux tubes in a dark QCD-like hidden sector with dark-quark masses above the confinement scale.

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Lorenzo Tranchedone, Ethan Carragher, Edward Hardy, Natálie Koscelanská van IJcken. 2026-01-07. Metastable cosmic strings are broken at the start. https://doi.org/10.1007/jhep07(2026)214

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