String Theory and the First Half of the Universe
The period between inflation and nucleosynthesis can last for thirty orders of magnitude of time and represent half the lifetime of the universe on a logarithmic scale. But yet, there are minimal observational constraints on this epoch. String cosmologies motivate a rich set of modifications from the standard radiation-dominated post-inflationary assumption of Lambda CDM. In particular, string cosmology suggests the likelihood of moduli-dominated cosmologies through kination, tracker and matter epochs. I review the possible scenarios and observational possibilities, including a novel percolation scenario for formation of cosmic string networks.