Speaker
Description
Topological defects can arise as remnants of symmetry-breaking phase transitions in the early universe, and field theories can admit defects beyond the conventional homotopy-based classification. Semilocal strings provide such an example: they are string-like defects that can form even when the fundamental group of the vacuum manifold is trivial. We present results from numerical lattice simulations of semilocal string networks, investigating their particle-radiation properties for the first time. We find that the networks efficiently radiate Nambu-Goldstone (NG) bosons with physical momenta of order the Hubble scale. Motivated by the interpretation of the endpoints of semilocal string segments as global-monopole-like objects, we further study global monopole networks and find that they exhibit similar Hubble-scale NG boson radiation. As a cosmological implication, we discuss a scenario in which these NG bosons acquire masses through soft-breaking terms and constitute dark matter via their non-thermal production from semilocal string networks.