Baeza-Ballesteros, J., Copeland, E. J., Figueroa, D. G., & Lizarraga, J. (2025). Particle and gravitational wave emission by local string loops: Lattice calculation. Phys. Rev. D, 112(4), 043540–13pp.
Abstract: Using lattice field simulations of the Abelian-Higgs model, we characterize the simultaneous emission of (scalar and gauge) particles and gravitational waves (GWs) by local string loops. We use network loops created in a phase transition, and artificial loops formed by either crossing straight-boosted or curved-static infinite strings. Loops decay via both particle and GW emission, on timescales Delta tdec proportional to Lp, where L is the loop length. For particle production, we find p sim 2 for artificial loops and p sim 1 for network loops, whilst for GW emission, we find p sim 1 for all loops. We find that below a critical length, artificial loops decay primarily through particle production, whilst for larger loops GW emission dominates. However, for network loops, which represent more realistic configurations, particle emission always dominates, as supported by our data with length-to-core ratios up to L/rc < 6000. Our results indicate that the GW background from a local string network should be greatly suppressed compared to estimations that ignore particle emission.
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Baeza-Ballesteros, J., Copeland, E. J., Figueroa, D. G., & Lizarraga, J. (2024). Gravitational wave emission from a cosmic string loop: Global case. Phys. Rev. D, 110(4), 043522–12pp.
Abstract: We study the simultaneous decay of global string loops into scalar particles (massless and massive modes) and gravitational waves (GWs). Using field-theory simulations in flat space-time of isolated loops with initial length similar to 80-1700 times their core width, we determine the power emitted into scalar particles, P phi , and GWs, P GW , and characterize the loop-decay timescale as a function of its initial length, energy, and angular momentum. We quantify infrared and ultraviolet lattice dependencies of our results. For all type of loops and initial conditions considered, GW emission is always suppressed compared to particles as P GW /P phi approximate to O(10)(v/mp)2 ( 10 )( v/m p ) 2 << 1, where v is the vacuum expectation value associated with string formation. These conclusions are robust for the length-to-width ratios considered, with no indication they should change if the ratio is increased. The results suggest that the GW background from a global string network, such as in dark-matter axion scenarios, will be suppressed compared to previous expectations.
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