A window for cosmic strings

Particle emission and gravitational radiation from cosmic string loops affect the resulting loop distribution, and hence the corresponding observational consequences of cosmic strings. Here we focus on models in which loops of all sizes are produced from the infinite string network with a given power-law (the Polchinski-Rocha loop production function). We find that, due to particle production, the Stochastic Gravitational Wave Background (SGWB) is cut off at frequencies larger than any current or planned GW experiment, meaning that present constraints from the LIGO-Virgo-Kagra (LVK) collaboration still hold. However, if a fraction $\gtrsim \mathcal{O}(10^{-3})$ of these particles cascades into $\gamma$-rays, and if the gravitational backreaction scale follows the Polchinski-Rocha model, then the string tension is tightly constrained from below by measurements of the Diffuse $\gamma$-Ray Background, and from above by the SGWB. With reasonable assumptions, the joint constraint on the string tension set by these two possible observables reduces the available parameter space to a narrow band. Future upgrades to LVK will either rule out this model or detect strings