A theoretical study explores the generation of gravitational waves from the decay of cosmic topological defects, such as monopoles, cosmic strings, and domain walls. These defects form in the early universe following gauge symmetry breakings, such as $SU(2) \to U(1) \to Z_2 \to 1$. The research focuses on how the evolution and decay of these structures, particularly string-bounded domain walls (WBS), produce a distinctive spectrum of gravitational waves that could be detectable.

The work details that the $SU(2) \to U(1)$ symmetry breaking generates monopoles with an elementary $U(1)$ magnetic flux, while the subsequent $U(1) \to Z_2$ breaking produces cosmic strings. These elementary strings and the resulting WBS emit gravitational waves. During their decay, the WBS yield a network of composite strings carrying the same $U(1)$ flux as the initial monopoles. This sequential formation and decay mechanism is crucial for understanding the properties of the emitted gravitational waves.

The authors present specific gravitational wave spectra for different cosmological scenarios, depending on whether the resulting composite strings are effectively stable, quasistable, or metastable. These three scenarios are also realized in an alternative symmetry breaking chain, $SU(3) \to SO(3) \to Z_2 \to 1$. Both $SU(2)$ and $SU(3)$ symmetry chains have been proposed in the literature as possible flavor gauge symmetries. The detection of these gravitational wave spectra could offer a unique window into the early universe's phase transitions and high-energy physics beyond the Standard Model.