Impact of cosmic evolution on the gravitational wave spectrum from cosmic strings

In the standard cosmological paradigm, the gravitational wave (GW) spectrum from a cosmic string network is well defined. However, early-Universe dynamics can significantly alter this relic signal. We systematically investigate how different new physics epochs in the radiation era–including extra relativistic degrees of freedom, early matter domination, intermediate vacuum domination, and kination–modify string network evolution and loop production. We find that a kination era enhances the stochastic GW signal, whereas the other scenarios suppress the signal to varying degrees. We also demonstrate that late-time dynamical dark energy has a negligible impact on the GW spectrum from cosmic strings.