Particle and gravitational wave emission by local string loops: Lattice calculation

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 $\mathrm{\ensuremath{\Delta}}{t}_{\mathrm{dec}}\ensuremath{\propto}{L}^{p}$, where $L$ is the loop length. For particle production, we find $p\ensuremath{\simeq}2$ for artificial loops and $p\ensuremath{\simeq}1$ for network loops, whilst for GW emission, we find $p\ensuremath{\simeq}1$ 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 $L/{r}_{\mathrm{c}}\ensuremath{\lesssim}6000$. Our results indicate that the GW background from a local string network should be greatly suppressed compared to estimations that ignore particle emission.