Monopoles on strings

In cosmological scenarios based on grand unification, string theory or braneworlds, many kinds of topological or non-topological defects, including monopoles and cosmic strings, are predicted to be formed in the early Universe. Here we review specifically the physics of composite objects involving monopoles tied to strings. There is a wide variety of these, including for example 'dumbbells' and 'necklaces', depending on how many strings attach to each monopole and on the extent to which the various fluxes are confined to the strings. We also briefly survey the prospects for observing such structures, the existing observational limits, and potential evidence for a cosmological role.