Perex
Cosmic strings are predicted in many particle physics models beyond the Standard Model. If such a model describes our universe, a network of strings inevitably forms in the early universe and persists to the present time. Cosmic strings lead to nonlinear density fluctuations at early times and will dominate the nonlinear structure at high redshifts. I will discuss how cosmic string loops dominate the halo mass function and can lead to early galaxy formation and to the formation of supermassive black holes at high redshifts. Long string segments lead to wakes which leave behind characteristic imprints in 21-cm redshift maps.